/* * CDDL HEADER START * * The contents of this file are subject to the terms of the * Common Development and Distribution License (the "License"). * You may not use this file except in compliance with the License. * * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE * or http://www.opensolaris.org/os/licensing. * See the License for the specific language governing permissions * and limitations under the License. * * When distributing Covered Code, include this CDDL HEADER in each * file and include the License file at usr/src/OPENSOLARIS.LICENSE. * If applicable, add the following below this CDDL HEADER, with the * fields enclosed by brackets "[]" replaced with your own identifying * information: Portions Copyright [yyyy] [name of copyright owner] * * CDDL HEADER END */ /* * Copyright 2008 Sun Microsystems, Inc. All rights reserved. * Use is subject to license terms. */ /* * DVA-based Adjustable Replacement Cache * * While much of the theory of operation used here is * based on the self-tuning, low overhead replacement cache * presented by Megiddo and Modha at FAST 2003, there are some * significant differences: * * 1. The Megiddo and Modha model assumes any page is evictable. * Pages in its cache cannot be "locked" into memory. This makes * the eviction algorithm simple: evict the last page in the list. * This also make the performance characteristics easy to reason * about. Our cache is not so simple. At any given moment, some * subset of the blocks in the cache are un-evictable because we * have handed out a reference to them. Blocks are only evictable * when there are no external references active. This makes * eviction far more problematic: we choose to evict the evictable * blocks that are the "lowest" in the list. * * There are times when it is not possible to evict the requested * space. In these circumstances we are unable to adjust the cache * size. To prevent the cache growing unbounded at these times we * implement a "cache throttle" that slows the flow of new data * into the cache until we can make space available. * * 2. The Megiddo and Modha model assumes a fixed cache size. * Pages are evicted when the cache is full and there is a cache * miss. Our model has a variable sized cache. It grows with * high use, but also tries to react to memory pressure from the * operating system: decreasing its size when system memory is * tight. * * 3. The Megiddo and Modha model assumes a fixed page size. All * elements of the cache are therefor exactly the same size. So * when adjusting the cache size following a cache miss, its simply * a matter of choosing a single page to evict. In our model, we * have variable sized cache blocks (rangeing from 512 bytes to * 128K bytes). We therefor choose a set of blocks to evict to make * space for a cache miss that approximates as closely as possible * the space used by the new block. * * See also: "ARC: A Self-Tuning, Low Overhead Replacement Cache" * by N. Megiddo & D. Modha, FAST 2003 */ /* * The locking model: * * A new reference to a cache buffer can be obtained in two * ways: 1) via a hash table lookup using the DVA as a key, * or 2) via one of the ARC lists. The arc_read() interface * uses method 1, while the internal arc algorithms for * adjusting the cache use method 2. We therefor provide two * types of locks: 1) the hash table lock array, and 2) the * arc list locks. * * Buffers do not have their own mutexs, rather they rely on the * hash table mutexs for the bulk of their protection (i.e. most * fields in the arc_buf_hdr_t are protected by these mutexs). * * buf_hash_find() returns the appropriate mutex (held) when it * locates the requested buffer in the hash table. It returns * NULL for the mutex if the buffer was not in the table. * * buf_hash_remove() expects the appropriate hash mutex to be * already held before it is invoked. * * Each arc state also has a mutex which is used to protect the * buffer list associated with the state. When attempting to * obtain a hash table lock while holding an arc list lock you * must use: mutex_tryenter() to avoid deadlock. Also note that * the active state mutex must be held before the ghost state mutex. * * Arc buffers may have an associated eviction callback function. * This function will be invoked prior to removing the buffer (e.g. * in arc_do_user_evicts()). Note however that the data associated * with the buffer may be evicted prior to the callback. The callback * must be made with *no locks held* (to prevent deadlock). Additionally, * the users of callbacks must ensure that their private data is * protected from simultaneous callbacks from arc_buf_evict() * and arc_do_user_evicts(). * * Note that the majority of the performance stats are manipulated * with atomic operations. * * The L2ARC uses the l2arc_buflist_mtx global mutex for the following: * * - L2ARC buflist creation * - L2ARC buflist eviction * - L2ARC write completion, which walks L2ARC buflists * - ARC header destruction, as it removes from L2ARC buflists * - ARC header release, as it removes from L2ARC buflists */ #include #include #include #include #include #include #include #ifdef _KERNEL #include #include #include #include #endif #include #include static kmutex_t arc_reclaim_thr_lock; static kcondvar_t arc_reclaim_thr_cv; /* used to signal reclaim thr */ static uint8_t arc_thread_exit; extern int zfs_write_limit_shift; extern uint64_t zfs_write_limit_max; extern kmutex_t zfs_write_limit_lock; #define ARC_REDUCE_DNLC_PERCENT 3 uint_t arc_reduce_dnlc_percent = ARC_REDUCE_DNLC_PERCENT; typedef enum arc_reclaim_strategy { ARC_RECLAIM_AGGR, /* Aggressive reclaim strategy */ ARC_RECLAIM_CONS /* Conservative reclaim strategy */ } arc_reclaim_strategy_t; /* number of seconds before growing cache again */ static int arc_grow_retry = 60; /* * minimum lifespan of a prefetch block in clock ticks * (initialized in arc_init()) */ static int arc_min_prefetch_lifespan; static int arc_dead; /* * The arc has filled available memory and has now warmed up. */ static boolean_t arc_warm; /* * These tunables are for performance analysis. */ uint64_t zfs_arc_max; uint64_t zfs_arc_min; uint64_t zfs_arc_meta_limit = 0; int zfs_mdcomp_disable = 0; /* * Note that buffers can be in one of 6 states: * ARC_anon - anonymous (discussed below) * ARC_mru - recently used, currently cached * ARC_mru_ghost - recentely used, no longer in cache * ARC_mfu - frequently used, currently cached * ARC_mfu_ghost - frequently used, no longer in cache * ARC_l2c_only - exists in L2ARC but not other states * When there are no active references to the buffer, they are * are linked onto a list in one of these arc states. These are * the only buffers that can be evicted or deleted. Within each * state there are multiple lists, one for meta-data and one for * non-meta-data. Meta-data (indirect blocks, blocks of dnodes, * etc.) is tracked separately so that it can be managed more * explicitly: favored over data, limited explicitly. * * Anonymous buffers are buffers that are not associated with * a DVA. These are buffers that hold dirty block copies * before they are written to stable storage. By definition, * they are "ref'd" and are considered part of arc_mru * that cannot be freed. Generally, they will aquire a DVA * as they are written and migrate onto the arc_mru list. * * The ARC_l2c_only state is for buffers that are in the second * level ARC but no longer in any of the ARC_m* lists. The second * level ARC itself may also contain buffers that are in any of * the ARC_m* states - meaning that a buffer can exist in two * places. The reason for the ARC_l2c_only state is to keep the * buffer header in the hash table, so that reads that hit the * second level ARC benefit from these fast lookups. */ typedef struct arc_state { list_t arcs_list[ARC_BUFC_NUMTYPES]; /* list of evictable buffers */ uint64_t arcs_lsize[ARC_BUFC_NUMTYPES]; /* amount of evictable data */ uint64_t arcs_size; /* total amount of data in this state */ kmutex_t arcs_mtx; } arc_state_t; /* The 6 states: */ static arc_state_t ARC_anon; static arc_state_t ARC_mru; static arc_state_t ARC_mru_ghost; static arc_state_t ARC_mfu; static arc_state_t ARC_mfu_ghost; static arc_state_t ARC_l2c_only; typedef struct arc_stats { kstat_named_t arcstat_hits; kstat_named_t arcstat_misses; kstat_named_t arcstat_demand_data_hits; kstat_named_t arcstat_demand_data_misses; kstat_named_t arcstat_demand_metadata_hits; kstat_named_t arcstat_demand_metadata_misses; kstat_named_t arcstat_prefetch_data_hits; kstat_named_t arcstat_prefetch_data_misses; kstat_named_t arcstat_prefetch_metadata_hits; kstat_named_t arcstat_prefetch_metadata_misses; kstat_named_t arcstat_mru_hits; kstat_named_t arcstat_mru_ghost_hits; kstat_named_t arcstat_mfu_hits; kstat_named_t arcstat_mfu_ghost_hits; kstat_named_t arcstat_deleted; kstat_named_t arcstat_recycle_miss; kstat_named_t arcstat_mutex_miss; kstat_named_t arcstat_evict_skip; kstat_named_t arcstat_hash_elements; kstat_named_t arcstat_hash_elements_max; kstat_named_t arcstat_hash_collisions; kstat_named_t arcstat_hash_chains; kstat_named_t arcstat_hash_chain_max; kstat_named_t arcstat_p; kstat_named_t arcstat_c; kstat_named_t arcstat_c_min; kstat_named_t arcstat_c_max; kstat_named_t arcstat_size; kstat_named_t arcstat_hdr_size; kstat_named_t arcstat_l2_hits; kstat_named_t arcstat_l2_misses; kstat_named_t arcstat_l2_feeds; kstat_named_t arcstat_l2_rw_clash; kstat_named_t arcstat_l2_writes_sent; kstat_named_t arcstat_l2_writes_done; kstat_named_t arcstat_l2_writes_error; kstat_named_t arcstat_l2_writes_hdr_miss; kstat_named_t arcstat_l2_evict_lock_retry; kstat_named_t arcstat_l2_evict_reading; kstat_named_t arcstat_l2_free_on_write; kstat_named_t arcstat_l2_abort_lowmem; kstat_named_t arcstat_l2_cksum_bad; kstat_named_t arcstat_l2_io_error; kstat_named_t arcstat_l2_size; kstat_named_t arcstat_l2_hdr_size; kstat_named_t arcstat_memory_throttle_count; } arc_stats_t; static arc_stats_t arc_stats = { { "hits", KSTAT_DATA_UINT64 }, { "misses", KSTAT_DATA_UINT64 }, { "demand_data_hits", KSTAT_DATA_UINT64 }, { "demand_data_misses", KSTAT_DATA_UINT64 }, { "demand_metadata_hits", KSTAT_DATA_UINT64 }, { "demand_metadata_misses", KSTAT_DATA_UINT64 }, { "prefetch_data_hits", KSTAT_DATA_UINT64 }, { "prefetch_data_misses", KSTAT_DATA_UINT64 }, { "prefetch_metadata_hits", KSTAT_DATA_UINT64 }, { "prefetch_metadata_misses", KSTAT_DATA_UINT64 }, { "mru_hits", KSTAT_DATA_UINT64 }, { "mru_ghost_hits", KSTAT_DATA_UINT64 }, { "mfu_hits", KSTAT_DATA_UINT64 }, { "mfu_ghost_hits", KSTAT_DATA_UINT64 }, { "deleted", KSTAT_DATA_UINT64 }, { "recycle_miss", KSTAT_DATA_UINT64 }, { "mutex_miss", KSTAT_DATA_UINT64 }, { "evict_skip", KSTAT_DATA_UINT64 }, { "hash_elements", KSTAT_DATA_UINT64 }, { "hash_elements_max", KSTAT_DATA_UINT64 }, { "hash_collisions", KSTAT_DATA_UINT64 }, { "hash_chains", KSTAT_DATA_UINT64 }, { "hash_chain_max", KSTAT_DATA_UINT64 }, { "p", KSTAT_DATA_UINT64 }, { "c", KSTAT_DATA_UINT64 }, { "c_min", KSTAT_DATA_UINT64 }, { "c_max", KSTAT_DATA_UINT64 }, { "size", KSTAT_DATA_UINT64 }, { "hdr_size", KSTAT_DATA_UINT64 }, { "l2_hits", KSTAT_DATA_UINT64 }, { "l2_misses", KSTAT_DATA_UINT64 }, { "l2_feeds", KSTAT_DATA_UINT64 }, { "l2_rw_clash", KSTAT_DATA_UINT64 }, { "l2_writes_sent", KSTAT_DATA_UINT64 }, { "l2_writes_done", KSTAT_DATA_UINT64 }, { "l2_writes_error", KSTAT_DATA_UINT64 }, { "l2_writes_hdr_miss", KSTAT_DATA_UINT64 }, { "l2_evict_lock_retry", KSTAT_DATA_UINT64 }, { "l2_evict_reading", KSTAT_DATA_UINT64 }, { "l2_free_on_write", KSTAT_DATA_UINT64 }, { "l2_abort_lowmem", KSTAT_DATA_UINT64 }, { "l2_cksum_bad", KSTAT_DATA_UINT64 }, { "l2_io_error", KSTAT_DATA_UINT64 }, { "l2_size", KSTAT_DATA_UINT64 }, { "l2_hdr_size", KSTAT_DATA_UINT64 }, { "memory_throttle_count", KSTAT_DATA_UINT64 } }; #define ARCSTAT(stat) (arc_stats.stat.value.ui64) #define ARCSTAT_INCR(stat, val) \ atomic_add_64(&arc_stats.stat.value.ui64, (val)); #define ARCSTAT_BUMP(stat) ARCSTAT_INCR(stat, 1) #define ARCSTAT_BUMPDOWN(stat) ARCSTAT_INCR(stat, -1) #define ARCSTAT_MAX(stat, val) { \ uint64_t m; \ while ((val) > (m = arc_stats.stat.value.ui64) && \ (m != atomic_cas_64(&arc_stats.stat.value.ui64, m, (val)))) \ continue; \ } #define ARCSTAT_MAXSTAT(stat) \ ARCSTAT_MAX(stat##_max, arc_stats.stat.value.ui64) /* * We define a macro to allow ARC hits/misses to be easily broken down by * two separate conditions, giving a total of four different subtypes for * each of hits and misses (so eight statistics total). */ #define ARCSTAT_CONDSTAT(cond1, stat1, notstat1, cond2, stat2, notstat2, stat) \ if (cond1) { \ if (cond2) { \ ARCSTAT_BUMP(arcstat_##stat1##_##stat2##_##stat); \ } else { \ ARCSTAT_BUMP(arcstat_##stat1##_##notstat2##_##stat); \ } \ } else { \ if (cond2) { \ ARCSTAT_BUMP(arcstat_##notstat1##_##stat2##_##stat); \ } else { \ ARCSTAT_BUMP(arcstat_##notstat1##_##notstat2##_##stat);\ } \ } kstat_t *arc_ksp; static arc_state_t *arc_anon; static arc_state_t *arc_mru; static arc_state_t *arc_mru_ghost; static arc_state_t *arc_mfu; static arc_state_t *arc_mfu_ghost; static arc_state_t *arc_l2c_only; /* * There are several ARC variables that are critical to export as kstats -- * but we don't want to have to grovel around in the kstat whenever we wish to * manipulate them. For these variables, we therefore define them to be in * terms of the statistic variable. This assures that we are not introducing * the possibility of inconsistency by having shadow copies of the variables, * while still allowing the code to be readable. */ #define arc_size ARCSTAT(arcstat_size) /* actual total arc size */ #define arc_p ARCSTAT(arcstat_p) /* target size of MRU */ #define arc_c ARCSTAT(arcstat_c) /* target size of cache */ #define arc_c_min ARCSTAT(arcstat_c_min) /* min target cache size */ #define arc_c_max ARCSTAT(arcstat_c_max) /* max target cache size */ static int arc_no_grow; /* Don't try to grow cache size */ static uint64_t arc_tempreserve; static uint64_t arc_meta_used; static uint64_t arc_meta_limit; static uint64_t arc_meta_max = 0; typedef struct l2arc_buf_hdr l2arc_buf_hdr_t; typedef struct arc_callback arc_callback_t; struct arc_callback { void *acb_private; arc_done_func_t *acb_done; arc_buf_t *acb_buf; zio_t *acb_zio_dummy; arc_callback_t *acb_next; }; typedef struct arc_write_callback arc_write_callback_t; struct arc_write_callback { void *awcb_private; arc_done_func_t *awcb_ready; arc_done_func_t *awcb_done; arc_buf_t *awcb_buf; }; struct arc_buf_hdr { /* protected by hash lock */ dva_t b_dva; uint64_t b_birth; uint64_t b_cksum0; kmutex_t b_freeze_lock; zio_cksum_t *b_freeze_cksum; arc_buf_hdr_t *b_hash_next; arc_buf_t *b_buf; uint32_t b_flags; uint32_t b_datacnt; arc_callback_t *b_acb; kcondvar_t b_cv; /* immutable */ arc_buf_contents_t b_type; uint64_t b_size; spa_t *b_spa; /* protected by arc state mutex */ arc_state_t *b_state; list_node_t b_arc_node; /* updated atomically */ clock_t b_arc_access; /* self protecting */ refcount_t b_refcnt; l2arc_buf_hdr_t *b_l2hdr; list_node_t b_l2node; }; static arc_buf_t *arc_eviction_list; static kmutex_t arc_eviction_mtx; static arc_buf_hdr_t arc_eviction_hdr; static void arc_get_data_buf(arc_buf_t *buf); static void arc_access(arc_buf_hdr_t *buf, kmutex_t *hash_lock); static int arc_evict_needed(arc_buf_contents_t type); static void arc_evict_ghost(arc_state_t *state, spa_t *spa, int64_t bytes); #define GHOST_STATE(state) \ ((state) == arc_mru_ghost || (state) == arc_mfu_ghost || \ (state) == arc_l2c_only) /* * Private ARC flags. These flags are private ARC only flags that will show up * in b_flags in the arc_hdr_buf_t. Some flags are publicly declared, and can * be passed in as arc_flags in things like arc_read. However, these flags * should never be passed and should only be set by ARC code. When adding new * public flags, make sure not to smash the private ones. */ #define ARC_IN_HASH_TABLE (1 << 9) /* this buffer is hashed */ #define ARC_IO_IN_PROGRESS (1 << 10) /* I/O in progress for buf */ #define ARC_IO_ERROR (1 << 11) /* I/O failed for buf */ #define ARC_FREED_IN_READ (1 << 12) /* buf freed while in read */ #define ARC_BUF_AVAILABLE (1 << 13) /* block not in active use */ #define ARC_INDIRECT (1 << 14) /* this is an indirect block */ #define ARC_FREE_IN_PROGRESS (1 << 15) /* hdr about to be freed */ #define ARC_L2_WRITING (1 << 16) /* L2ARC write in progress */ #define ARC_L2_EVICTED (1 << 17) /* evicted during I/O */ #define ARC_L2_WRITE_HEAD (1 << 18) /* head of write list */ #define ARC_STORED (1 << 19) /* has been store()d to */ #define HDR_IN_HASH_TABLE(hdr) ((hdr)->b_flags & ARC_IN_HASH_TABLE) #define HDR_IO_IN_PROGRESS(hdr) ((hdr)->b_flags & ARC_IO_IN_PROGRESS) #define HDR_IO_ERROR(hdr) ((hdr)->b_flags & ARC_IO_ERROR) #define HDR_FREED_IN_READ(hdr) ((hdr)->b_flags & ARC_FREED_IN_READ) #define HDR_BUF_AVAILABLE(hdr) ((hdr)->b_flags & ARC_BUF_AVAILABLE) #define HDR_FREE_IN_PROGRESS(hdr) ((hdr)->b_flags & ARC_FREE_IN_PROGRESS) #define HDR_L2CACHE(hdr) ((hdr)->b_flags & ARC_L2CACHE) #define HDR_L2_READING(hdr) ((hdr)->b_flags & ARC_IO_IN_PROGRESS && \ (hdr)->b_l2hdr != NULL) #define HDR_L2_WRITING(hdr) ((hdr)->b_flags & ARC_L2_WRITING) #define HDR_L2_EVICTED(hdr) ((hdr)->b_flags & ARC_L2_EVICTED) #define HDR_L2_WRITE_HEAD(hdr) ((hdr)->b_flags & ARC_L2_WRITE_HEAD) /* * Other sizes */ #define HDR_SIZE ((int64_t)sizeof (arc_buf_hdr_t)) #define L2HDR_SIZE ((int64_t)sizeof (l2arc_buf_hdr_t)) /* * Hash table routines */ #define HT_LOCK_PAD 64 struct ht_lock { kmutex_t ht_lock; #ifdef _KERNEL unsigned char pad[(HT_LOCK_PAD - sizeof (kmutex_t))]; #endif }; #define BUF_LOCKS 256 typedef struct buf_hash_table { uint64_t ht_mask; arc_buf_hdr_t **ht_table; struct ht_lock ht_locks[BUF_LOCKS]; } buf_hash_table_t; static buf_hash_table_t buf_hash_table; #define BUF_HASH_INDEX(spa, dva, birth) \ (buf_hash(spa, dva, birth) & buf_hash_table.ht_mask) #define BUF_HASH_LOCK_NTRY(idx) (buf_hash_table.ht_locks[idx & (BUF_LOCKS-1)]) #define BUF_HASH_LOCK(idx) (&(BUF_HASH_LOCK_NTRY(idx).ht_lock)) #define HDR_LOCK(buf) \ (BUF_HASH_LOCK(BUF_HASH_INDEX(buf->b_spa, &buf->b_dva, buf->b_birth))) uint64_t zfs_crc64_table[256]; /* * Level 2 ARC */ #define L2ARC_WRITE_SIZE (8 * 1024 * 1024) /* initial write max */ #define L2ARC_HEADROOM 4 /* num of writes */ #define L2ARC_FEED_SECS 1 /* caching interval */ #define l2arc_writes_sent ARCSTAT(arcstat_l2_writes_sent) #define l2arc_writes_done ARCSTAT(arcstat_l2_writes_done) /* * L2ARC Performance Tunables */ uint64_t l2arc_write_max = L2ARC_WRITE_SIZE; /* default max write size */ uint64_t l2arc_write_boost = L2ARC_WRITE_SIZE; /* extra write during warmup */ uint64_t l2arc_headroom = L2ARC_HEADROOM; /* number of dev writes */ uint64_t l2arc_feed_secs = L2ARC_FEED_SECS; /* interval seconds */ boolean_t l2arc_noprefetch = B_TRUE; /* don't cache prefetch bufs */ /* * L2ARC Internals */ typedef struct l2arc_dev { vdev_t *l2ad_vdev; /* vdev */ spa_t *l2ad_spa; /* spa */ uint64_t l2ad_hand; /* next write location */ uint64_t l2ad_write; /* desired write size, bytes */ uint64_t l2ad_boost; /* warmup write boost, bytes */ uint64_t l2ad_start; /* first addr on device */ uint64_t l2ad_end; /* last addr on device */ uint64_t l2ad_evict; /* last addr eviction reached */ boolean_t l2ad_first; /* first sweep through */ list_t *l2ad_buflist; /* buffer list */ list_node_t l2ad_node; /* device list node */ } l2arc_dev_t; static list_t L2ARC_dev_list; /* device list */ static list_t *l2arc_dev_list; /* device list pointer */ static kmutex_t l2arc_dev_mtx; /* device list mutex */ static l2arc_dev_t *l2arc_dev_last; /* last device used */ static kmutex_t l2arc_buflist_mtx; /* mutex for all buflists */ static list_t L2ARC_free_on_write; /* free after write buf list */ static list_t *l2arc_free_on_write; /* free after write list ptr */ static kmutex_t l2arc_free_on_write_mtx; /* mutex for list */ static uint64_t l2arc_ndev; /* number of devices */ typedef struct l2arc_read_callback { arc_buf_t *l2rcb_buf; /* read buffer */ spa_t *l2rcb_spa; /* spa */ blkptr_t l2rcb_bp; /* original blkptr */ zbookmark_t l2rcb_zb; /* original bookmark */ int l2rcb_flags; /* original flags */ } l2arc_read_callback_t; typedef struct l2arc_write_callback { l2arc_dev_t *l2wcb_dev; /* device info */ arc_buf_hdr_t *l2wcb_head; /* head of write buflist */ } l2arc_write_callback_t; struct l2arc_buf_hdr { /* protected by arc_buf_hdr mutex */ l2arc_dev_t *b_dev; /* L2ARC device */ daddr_t b_daddr; /* disk address, offset byte */ }; typedef struct l2arc_data_free { /* protected by l2arc_free_on_write_mtx */ void *l2df_data; size_t l2df_size; void (*l2df_func)(void *, size_t); list_node_t l2df_list_node; } l2arc_data_free_t; static kmutex_t l2arc_feed_thr_lock; static kcondvar_t l2arc_feed_thr_cv; static uint8_t l2arc_thread_exit; static void l2arc_read_done(zio_t *zio); static void l2arc_hdr_stat_add(void); static void l2arc_hdr_stat_remove(void); static uint64_t buf_hash(spa_t *spa, const dva_t *dva, uint64_t birth) { uintptr_t spav = (uintptr_t)spa; uint8_t *vdva = (uint8_t *)dva; uint64_t crc = -1ULL; int i; ASSERT(zfs_crc64_table[128] == ZFS_CRC64_POLY); for (i = 0; i < sizeof (dva_t); i++) crc = (crc >> 8) ^ zfs_crc64_table[(crc ^ vdva[i]) & 0xFF]; crc ^= (spav>>8) ^ birth; return (crc); } #define BUF_EMPTY(buf) \ ((buf)->b_dva.dva_word[0] == 0 && \ (buf)->b_dva.dva_word[1] == 0 && \ (buf)->b_birth == 0) #define BUF_EQUAL(spa, dva, birth, buf) \ ((buf)->b_dva.dva_word[0] == (dva)->dva_word[0]) && \ ((buf)->b_dva.dva_word[1] == (dva)->dva_word[1]) && \ ((buf)->b_birth == birth) && ((buf)->b_spa == spa) static arc_buf_hdr_t * buf_hash_find(spa_t *spa, const dva_t *dva, uint64_t birth, kmutex_t **lockp) { uint64_t idx = BUF_HASH_INDEX(spa, dva, birth); kmutex_t *hash_lock = BUF_HASH_LOCK(idx); arc_buf_hdr_t *buf; mutex_enter(hash_lock); for (buf = buf_hash_table.ht_table[idx]; buf != NULL; buf = buf->b_hash_next) { if (BUF_EQUAL(spa, dva, birth, buf)) { *lockp = hash_lock; return (buf); } } mutex_exit(hash_lock); *lockp = NULL; return (NULL); } /* * Insert an entry into the hash table. If there is already an element * equal to elem in the hash table, then the already existing element * will be returned and the new element will not be inserted. * Otherwise returns NULL. */ static arc_buf_hdr_t * buf_hash_insert(arc_buf_hdr_t *buf, kmutex_t **lockp) { uint64_t idx = BUF_HASH_INDEX(buf->b_spa, &buf->b_dva, buf->b_birth); kmutex_t *hash_lock = BUF_HASH_LOCK(idx); arc_buf_hdr_t *fbuf; uint32_t i; ASSERT(!HDR_IN_HASH_TABLE(buf)); *lockp = hash_lock; mutex_enter(hash_lock); for (fbuf = buf_hash_table.ht_table[idx], i = 0; fbuf != NULL; fbuf = fbuf->b_hash_next, i++) { if (BUF_EQUAL(buf->b_spa, &buf->b_dva, buf->b_birth, fbuf)) return (fbuf); } buf->b_hash_next = buf_hash_table.ht_table[idx]; buf_hash_table.ht_table[idx] = buf; buf->b_flags |= ARC_IN_HASH_TABLE; /* collect some hash table performance data */ if (i > 0) { ARCSTAT_BUMP(arcstat_hash_collisions); if (i == 1) ARCSTAT_BUMP(arcstat_hash_chains); ARCSTAT_MAX(arcstat_hash_chain_max, i); } ARCSTAT_BUMP(arcstat_hash_elements); ARCSTAT_MAXSTAT(arcstat_hash_elements); return (NULL); } static void buf_hash_remove(arc_buf_hdr_t *buf) { arc_buf_hdr_t *fbuf, **bufp; uint64_t idx = BUF_HASH_INDEX(buf->b_spa, &buf->b_dva, buf->b_birth); ASSERT(MUTEX_HELD(BUF_HASH_LOCK(idx))); ASSERT(HDR_IN_HASH_TABLE(buf)); bufp = &buf_hash_table.ht_table[idx]; while ((fbuf = *bufp) != buf) { ASSERT(fbuf != NULL); bufp = &fbuf->b_hash_next; } *bufp = buf->b_hash_next; buf->b_hash_next = NULL; buf->b_flags &= ~ARC_IN_HASH_TABLE; /* collect some hash table performance data */ ARCSTAT_BUMPDOWN(arcstat_hash_elements); if (buf_hash_table.ht_table[idx] && buf_hash_table.ht_table[idx]->b_hash_next == NULL) ARCSTAT_BUMPDOWN(arcstat_hash_chains); } /* * Global data structures and functions for the buf kmem cache. */ static kmem_cache_t *hdr_cache; static kmem_cache_t *buf_cache; static void buf_fini(void) { int i; kmem_free(buf_hash_table.ht_table, (buf_hash_table.ht_mask + 1) * sizeof (void *)); for (i = 0; i < BUF_LOCKS; i++) mutex_destroy(&buf_hash_table.ht_locks[i].ht_lock); kmem_cache_destroy(hdr_cache); kmem_cache_destroy(buf_cache); } /* * Constructor callback - called when the cache is empty * and a new buf is requested. */ /* ARGSUSED */ static int hdr_cons(void *vbuf, void *unused, int kmflag) { arc_buf_hdr_t *buf = vbuf; bzero(buf, sizeof (arc_buf_hdr_t)); refcount_create(&buf->b_refcnt); cv_init(&buf->b_cv, NULL, CV_DEFAULT, NULL); mutex_init(&buf->b_freeze_lock, NULL, MUTEX_DEFAULT, NULL); ARCSTAT_INCR(arcstat_hdr_size, HDR_SIZE); return (0); } /* ARGSUSED */ static int buf_cons(void *vbuf, void *unused, int kmflag) { arc_buf_t *buf = vbuf; bzero(buf, sizeof (arc_buf_t)); rw_init(&buf->b_lock, NULL, RW_DEFAULT, NULL); return (0); } /* * Destructor callback - called when a cached buf is * no longer required. */ /* ARGSUSED */ static void hdr_dest(void *vbuf, void *unused) { arc_buf_hdr_t *buf = vbuf; refcount_destroy(&buf->b_refcnt); cv_destroy(&buf->b_cv); mutex_destroy(&buf->b_freeze_lock); ARCSTAT_INCR(arcstat_hdr_size, -HDR_SIZE); } /* ARGSUSED */ static void buf_dest(void *vbuf, void *unused) { arc_buf_t *buf = vbuf; rw_destroy(&buf->b_lock); } /* * Reclaim callback -- invoked when memory is low. */ /* ARGSUSED */ static void hdr_recl(void *unused) { dprintf("hdr_recl called\n"); /* * umem calls the reclaim func when we destroy the buf cache, * which is after we do arc_fini(). */ if (!arc_dead) cv_signal(&arc_reclaim_thr_cv); } static void buf_init(void) { uint64_t *ct; uint64_t hsize = 1ULL << 12; int i, j; /* * The hash table is big enough to fill all of physical memory * with an average 64K block size. The table will take up * totalmem*sizeof(void*)/64K (eg. 128KB/GB with 8-byte pointers). */ while (hsize * 65536 < physmem * PAGESIZE) hsize <<= 1; retry: buf_hash_table.ht_mask = hsize - 1; buf_hash_table.ht_table = kmem_zalloc(hsize * sizeof (void*), KM_NOSLEEP); if (buf_hash_table.ht_table == NULL) { ASSERT(hsize > (1ULL << 8)); hsize >>= 1; goto retry; } hdr_cache = kmem_cache_create("arc_buf_hdr_t", sizeof (arc_buf_hdr_t), 0, hdr_cons, hdr_dest, hdr_recl, NULL, NULL, 0); buf_cache = kmem_cache_create("arc_buf_t", sizeof (arc_buf_t), 0, buf_cons, buf_dest, NULL, NULL, NULL, 0); for (i = 0; i < 256; i++) for (ct = zfs_crc64_table + i, *ct = i, j = 8; j > 0; j--) *ct = (*ct >> 1) ^ (-(*ct & 1) & ZFS_CRC64_POLY); for (i = 0; i < BUF_LOCKS; i++) { mutex_init(&buf_hash_table.ht_locks[i].ht_lock, NULL, MUTEX_DEFAULT, NULL); } } #define ARC_MINTIME (hz>>4) /* 62 ms */ static void arc_cksum_verify(arc_buf_t *buf) { zio_cksum_t zc; if (!(zfs_flags & ZFS_DEBUG_MODIFY)) return; mutex_enter(&buf->b_hdr->b_freeze_lock); if (buf->b_hdr->b_freeze_cksum == NULL || (buf->b_hdr->b_flags & ARC_IO_ERROR)) { mutex_exit(&buf->b_hdr->b_freeze_lock); return; } fletcher_2_native(buf->b_data, buf->b_hdr->b_size, &zc); if (!ZIO_CHECKSUM_EQUAL(*buf->b_hdr->b_freeze_cksum, zc)) panic("buffer modified while frozen!"); mutex_exit(&buf->b_hdr->b_freeze_lock); } static int arc_cksum_equal(arc_buf_t *buf) { zio_cksum_t zc; int equal; mutex_enter(&buf->b_hdr->b_freeze_lock); fletcher_2_native(buf->b_data, buf->b_hdr->b_size, &zc); equal = ZIO_CHECKSUM_EQUAL(*buf->b_hdr->b_freeze_cksum, zc); mutex_exit(&buf->b_hdr->b_freeze_lock); return (equal); } static void arc_cksum_compute(arc_buf_t *buf, boolean_t force) { if (!force && !(zfs_flags & ZFS_DEBUG_MODIFY)) return; mutex_enter(&buf->b_hdr->b_freeze_lock); if (buf->b_hdr->b_freeze_cksum != NULL) { mutex_exit(&buf->b_hdr->b_freeze_lock); return; } buf->b_hdr->b_freeze_cksum = kmem_alloc(sizeof (zio_cksum_t), KM_SLEEP); fletcher_2_native(buf->b_data, buf->b_hdr->b_size, buf->b_hdr->b_freeze_cksum); mutex_exit(&buf->b_hdr->b_freeze_lock); } void arc_buf_thaw(arc_buf_t *buf) { if (zfs_flags & ZFS_DEBUG_MODIFY) { if (buf->b_hdr->b_state != arc_anon) panic("modifying non-anon buffer!"); if (buf->b_hdr->b_flags & ARC_IO_IN_PROGRESS) panic("modifying buffer while i/o in progress!"); arc_cksum_verify(buf); } mutex_enter(&buf->b_hdr->b_freeze_lock); if (buf->b_hdr->b_freeze_cksum != NULL) { kmem_free(buf->b_hdr->b_freeze_cksum, sizeof (zio_cksum_t)); buf->b_hdr->b_freeze_cksum = NULL; } mutex_exit(&buf->b_hdr->b_freeze_lock); } void arc_buf_freeze(arc_buf_t *buf) { if (!(zfs_flags & ZFS_DEBUG_MODIFY)) return; ASSERT(buf->b_hdr->b_freeze_cksum != NULL || buf->b_hdr->b_state == arc_anon); arc_cksum_compute(buf, B_FALSE); } static void add_reference(arc_buf_hdr_t *ab, kmutex_t *hash_lock, void *tag) { ASSERT(MUTEX_HELD(hash_lock)); if ((refcount_add(&ab->b_refcnt, tag) == 1) && (ab->b_state != arc_anon)) { uint64_t delta = ab->b_size * ab->b_datacnt; list_t *list = &ab->b_state->arcs_list[ab->b_type]; uint64_t *size = &ab->b_state->arcs_lsize[ab->b_type]; ASSERT(!MUTEX_HELD(&ab->b_state->arcs_mtx)); mutex_enter(&ab->b_state->arcs_mtx); ASSERT(list_link_active(&ab->b_arc_node)); list_remove(list, ab); if (GHOST_STATE(ab->b_state)) { ASSERT3U(ab->b_datacnt, ==, 0); ASSERT3P(ab->b_buf, ==, NULL); delta = ab->b_size; } ASSERT(delta > 0); ASSERT3U(*size, >=, delta); atomic_add_64(size, -delta); mutex_exit(&ab->b_state->arcs_mtx); /* remove the prefetch flag if we get a reference */ if (ab->b_flags & ARC_PREFETCH) ab->b_flags &= ~ARC_PREFETCH; } } static int remove_reference(arc_buf_hdr_t *ab, kmutex_t *hash_lock, void *tag) { int cnt; arc_state_t *state = ab->b_state; ASSERT(state == arc_anon || MUTEX_HELD(hash_lock)); ASSERT(!GHOST_STATE(state)); if (((cnt = refcount_remove(&ab->b_refcnt, tag)) == 0) && (state != arc_anon)) { uint64_t *size = &state->arcs_lsize[ab->b_type]; ASSERT(!MUTEX_HELD(&state->arcs_mtx)); mutex_enter(&state->arcs_mtx); ASSERT(!list_link_active(&ab->b_arc_node)); list_insert_head(&state->arcs_list[ab->b_type], ab); ASSERT(ab->b_datacnt > 0); atomic_add_64(size, ab->b_size * ab->b_datacnt); mutex_exit(&state->arcs_mtx); } return (cnt); } /* * Move the supplied buffer to the indicated state. The mutex * for the buffer must be held by the caller. */ static void arc_change_state(arc_state_t *new_state, arc_buf_hdr_t *ab, kmutex_t *hash_lock) { arc_state_t *old_state = ab->b_state; int64_t refcnt = refcount_count(&ab->b_refcnt); uint64_t from_delta, to_delta; ASSERT(MUTEX_HELD(hash_lock)); ASSERT(new_state != old_state); ASSERT(refcnt == 0 || ab->b_datacnt > 0); ASSERT(ab->b_datacnt == 0 || !GHOST_STATE(new_state)); from_delta = to_delta = ab->b_datacnt * ab->b_size; /* * If this buffer is evictable, transfer it from the * old state list to the new state list. */ if (refcnt == 0) { if (old_state != arc_anon) { int use_mutex = !MUTEX_HELD(&old_state->arcs_mtx); uint64_t *size = &old_state->arcs_lsize[ab->b_type]; if (use_mutex) mutex_enter(&old_state->arcs_mtx); ASSERT(list_link_active(&ab->b_arc_node)); list_remove(&old_state->arcs_list[ab->b_type], ab); /* * If prefetching out of the ghost cache, * we will have a non-null datacnt. */ if (GHOST_STATE(old_state) && ab->b_datacnt == 0) { /* ghost elements have a ghost size */ ASSERT(ab->b_buf == NULL); from_delta = ab->b_size; } ASSERT3U(*size, >=, from_delta); atomic_add_64(size, -from_delta); if (use_mutex) mutex_exit(&old_state->arcs_mtx); } if (new_state != arc_anon) { int use_mutex = !MUTEX_HELD(&new_state->arcs_mtx); uint64_t *size = &new_state->arcs_lsize[ab->b_type]; if (use_mutex) mutex_enter(&new_state->arcs_mtx); list_insert_head(&new_state->arcs_list[ab->b_type], ab); /* ghost elements have a ghost size */ if (GHOST_STATE(new_state)) { ASSERT(ab->b_datacnt == 0); ASSERT(ab->b_buf == NULL); to_delta = ab->b_size; } atomic_add_64(size, to_delta); if (use_mutex) mutex_exit(&new_state->arcs_mtx); } } ASSERT(!BUF_EMPTY(ab)); if (new_state == arc_anon) { buf_hash_remove(ab); } /* adjust state sizes */ if (to_delta) atomic_add_64(&new_state->arcs_size, to_delta); if (from_delta) { ASSERT3U(old_state->arcs_size, >=, from_delta); atomic_add_64(&old_state->arcs_size, -from_delta); } ab->b_state = new_state; /* adjust l2arc hdr stats */ if (new_state == arc_l2c_only) l2arc_hdr_stat_add(); else if (old_state == arc_l2c_only) l2arc_hdr_stat_remove(); } void arc_space_consume(uint64_t space) { atomic_add_64(&arc_meta_used, space); atomic_add_64(&arc_size, space); } void arc_space_return(uint64_t space) { ASSERT(arc_meta_used >= space); if (arc_meta_max < arc_meta_used) arc_meta_max = arc_meta_used; atomic_add_64(&arc_meta_used, -space); ASSERT(arc_size >= space); atomic_add_64(&arc_size, -space); } void * arc_data_buf_alloc(uint64_t size) { if (arc_evict_needed(ARC_BUFC_DATA)) cv_signal(&arc_reclaim_thr_cv); atomic_add_64(&arc_size, size); return (zio_data_buf_alloc(size)); } void arc_data_buf_free(void *buf, uint64_t size) { zio_data_buf_free(buf, size); ASSERT(arc_size >= size); atomic_add_64(&arc_size, -size); } arc_buf_t * arc_buf_alloc(spa_t *spa, int size, void *tag, arc_buf_contents_t type) { arc_buf_hdr_t *hdr; arc_buf_t *buf; ASSERT3U(size, >, 0); hdr = kmem_cache_alloc(hdr_cache, KM_PUSHPAGE); ASSERT(BUF_EMPTY(hdr)); hdr->b_size = size; hdr->b_type = type; hdr->b_spa = spa; hdr->b_state = arc_anon; hdr->b_arc_access = 0; buf = kmem_cache_alloc(buf_cache, KM_PUSHPAGE); buf->b_hdr = hdr; buf->b_data = NULL; buf->b_efunc = NULL; buf->b_private = NULL; buf->b_next = NULL; hdr->b_buf = buf; arc_get_data_buf(buf); hdr->b_datacnt = 1; hdr->b_flags = 0; ASSERT(refcount_is_zero(&hdr->b_refcnt)); (void) refcount_add(&hdr->b_refcnt, tag); return (buf); } static arc_buf_t * arc_buf_clone(arc_buf_t *from) { arc_buf_t *buf; arc_buf_hdr_t *hdr = from->b_hdr; uint64_t size = hdr->b_size; buf = kmem_cache_alloc(buf_cache, KM_PUSHPAGE); buf->b_hdr = hdr; buf->b_data = NULL; buf->b_efunc = NULL; buf->b_private = NULL; buf->b_next = hdr->b_buf; hdr->b_buf = buf; arc_get_data_buf(buf); bcopy(from->b_data, buf->b_data, size); hdr->b_datacnt += 1; return (buf); } void arc_buf_add_ref(arc_buf_t *buf, void* tag) { arc_buf_hdr_t *hdr; kmutex_t *hash_lock; /* * Check to see if this buffer is evicted. Callers * must verify b_data != NULL to know if the add_ref * was successful. */ rw_enter(&buf->b_lock, RW_READER); if (buf->b_data == NULL) { rw_exit(&buf->b_lock); return; } hdr = buf->b_hdr; ASSERT(hdr != NULL); hash_lock = HDR_LOCK(hdr); mutex_enter(hash_lock); rw_exit(&buf->b_lock); ASSERT(hdr->b_state == arc_mru || hdr->b_state == arc_mfu); add_reference(hdr, hash_lock, tag); arc_access(hdr, hash_lock); mutex_exit(hash_lock); ARCSTAT_BUMP(arcstat_hits); ARCSTAT_CONDSTAT(!(hdr->b_flags & ARC_PREFETCH), demand, prefetch, hdr->b_type != ARC_BUFC_METADATA, data, metadata, hits); } /* * Free the arc data buffer. If it is an l2arc write in progress, * the buffer is placed on l2arc_free_on_write to be freed later. */ static void arc_buf_data_free(arc_buf_hdr_t *hdr, void (*free_func)(void *, size_t), void *data, size_t size) { if (HDR_L2_WRITING(hdr)) { l2arc_data_free_t *df; df = kmem_alloc(sizeof (l2arc_data_free_t), KM_SLEEP); df->l2df_data = data; df->l2df_size = size; df->l2df_func = free_func; mutex_enter(&l2arc_free_on_write_mtx); list_insert_head(l2arc_free_on_write, df); mutex_exit(&l2arc_free_on_write_mtx); ARCSTAT_BUMP(arcstat_l2_free_on_write); } else { free_func(data, size); } } static void arc_buf_destroy(arc_buf_t *buf, boolean_t recycle, boolean_t all) { arc_buf_t **bufp; /* free up data associated with the buf */ if (buf->b_data) { arc_state_t *state = buf->b_hdr->b_state; uint64_t size = buf->b_hdr->b_size; arc_buf_contents_t type = buf->b_hdr->b_type; arc_cksum_verify(buf); if (!recycle) { if (type == ARC_BUFC_METADATA) { arc_buf_data_free(buf->b_hdr, zio_buf_free, buf->b_data, size); arc_space_return(size); } else { ASSERT(type == ARC_BUFC_DATA); arc_buf_data_free(buf->b_hdr, zio_data_buf_free, buf->b_data, size); atomic_add_64(&arc_size, -size); } } if (list_link_active(&buf->b_hdr->b_arc_node)) { uint64_t *cnt = &state->arcs_lsize[type]; ASSERT(refcount_is_zero(&buf->b_hdr->b_refcnt)); ASSERT(state != arc_anon); ASSERT3U(*cnt, >=, size); atomic_add_64(cnt, -size); } ASSERT3U(state->arcs_size, >=, size); atomic_add_64(&state->arcs_size, -size); buf->b_data = NULL; ASSERT(buf->b_hdr->b_datacnt > 0); buf->b_hdr->b_datacnt -= 1; } /* only remove the buf if requested */ if (!all) return; /* remove the buf from the hdr list */ for (bufp = &buf->b_hdr->b_buf; *bufp != buf; bufp = &(*bufp)->b_next) continue; *bufp = buf->b_next; ASSERT(buf->b_efunc == NULL); /* clean up the buf */ buf->b_hdr = NULL; kmem_cache_free(buf_cache, buf); } static void arc_hdr_destroy(arc_buf_hdr_t *hdr) { ASSERT(refcount_is_zero(&hdr->b_refcnt)); ASSERT3P(hdr->b_state, ==, arc_anon); ASSERT(!HDR_IO_IN_PROGRESS(hdr)); ASSERT(!(hdr->b_flags & ARC_STORED)); if (hdr->b_l2hdr != NULL) { if (!MUTEX_HELD(&l2arc_buflist_mtx)) { /* * To prevent arc_free() and l2arc_evict() from * attempting to free the same buffer at the same time, * a FREE_IN_PROGRESS flag is given to arc_free() to * give it priority. l2arc_evict() can't destroy this * header while we are waiting on l2arc_buflist_mtx. * * The hdr may be removed from l2ad_buflist before we * grab l2arc_buflist_mtx, so b_l2hdr is rechecked. */ mutex_enter(&l2arc_buflist_mtx); if (hdr->b_l2hdr != NULL) { list_remove(hdr->b_l2hdr->b_dev->l2ad_buflist, hdr); } mutex_exit(&l2arc_buflist_mtx); } else { list_remove(hdr->b_l2hdr->b_dev->l2ad_buflist, hdr); } ARCSTAT_INCR(arcstat_l2_size, -hdr->b_size); kmem_free(hdr->b_l2hdr, sizeof (l2arc_buf_hdr_t)); if (hdr->b_state == arc_l2c_only) l2arc_hdr_stat_remove(); hdr->b_l2hdr = NULL; } if (!BUF_EMPTY(hdr)) { ASSERT(!HDR_IN_HASH_TABLE(hdr)); bzero(&hdr->b_dva, sizeof (dva_t)); hdr->b_birth = 0; hdr->b_cksum0 = 0; } while (hdr->b_buf) { arc_buf_t *buf = hdr->b_buf; if (buf->b_efunc) { mutex_enter(&arc_eviction_mtx); rw_enter(&buf->b_lock, RW_WRITER); ASSERT(buf->b_hdr != NULL); arc_buf_destroy(hdr->b_buf, FALSE, FALSE); hdr->b_buf = buf->b_next; buf->b_hdr = &arc_eviction_hdr; buf->b_next = arc_eviction_list; arc_eviction_list = buf; rw_exit(&buf->b_lock); mutex_exit(&arc_eviction_mtx); } else { arc_buf_destroy(hdr->b_buf, FALSE, TRUE); } } if (hdr->b_freeze_cksum != NULL) { kmem_free(hdr->b_freeze_cksum, sizeof (zio_cksum_t)); hdr->b_freeze_cksum = NULL; } ASSERT(!list_link_active(&hdr->b_arc_node)); ASSERT3P(hdr->b_hash_next, ==, NULL); ASSERT3P(hdr->b_acb, ==, NULL); kmem_cache_free(hdr_cache, hdr); } void arc_buf_free(arc_buf_t *buf, void *tag) { arc_buf_hdr_t *hdr = buf->b_hdr; int hashed = hdr->b_state != arc_anon; ASSERT(buf->b_efunc == NULL); ASSERT(buf->b_data != NULL); if (hashed) { kmutex_t *hash_lock = HDR_LOCK(hdr); mutex_enter(hash_lock); (void) remove_reference(hdr, hash_lock, tag); if (hdr->b_datacnt > 1) arc_buf_destroy(buf, FALSE, TRUE); else hdr->b_flags |= ARC_BUF_AVAILABLE; mutex_exit(hash_lock); } else if (HDR_IO_IN_PROGRESS(hdr)) { int destroy_hdr; /* * We are in the middle of an async write. Don't destroy * this buffer unless the write completes before we finish * decrementing the reference count. */ mutex_enter(&arc_eviction_mtx); (void) remove_reference(hdr, NULL, tag); ASSERT(refcount_is_zero(&hdr->b_refcnt)); destroy_hdr = !HDR_IO_IN_PROGRESS(hdr); mutex_exit(&arc_eviction_mtx); if (destroy_hdr) arc_hdr_destroy(hdr); } else { if (remove_reference(hdr, NULL, tag) > 0) { ASSERT(HDR_IO_ERROR(hdr)); arc_buf_destroy(buf, FALSE, TRUE); } else { arc_hdr_destroy(hdr); } } } int arc_buf_remove_ref(arc_buf_t *buf, void* tag) { arc_buf_hdr_t *hdr = buf->b_hdr; kmutex_t *hash_lock = HDR_LOCK(hdr); int no_callback = (buf->b_efunc == NULL); if (hdr->b_state == arc_anon) { arc_buf_free(buf, tag); return (no_callback); } mutex_enter(hash_lock); ASSERT(hdr->b_state != arc_anon); ASSERT(buf->b_data != NULL); (void) remove_reference(hdr, hash_lock, tag); if (hdr->b_datacnt > 1) { if (no_callback) arc_buf_destroy(buf, FALSE, TRUE); } else if (no_callback) { ASSERT(hdr->b_buf == buf && buf->b_next == NULL); hdr->b_flags |= ARC_BUF_AVAILABLE; } ASSERT(no_callback || hdr->b_datacnt > 1 || refcount_is_zero(&hdr->b_refcnt)); mutex_exit(hash_lock); return (no_callback); } int arc_buf_size(arc_buf_t *buf) { return (buf->b_hdr->b_size); } /* * Evict buffers from list until we've removed the specified number of * bytes. Move the removed buffers to the appropriate evict state. * If the recycle flag is set, then attempt to "recycle" a buffer: * - look for a buffer to evict that is `bytes' long. * - return the data block from this buffer rather than freeing it. * This flag is used by callers that are trying to make space for a * new buffer in a full arc cache. * * This function makes a "best effort". It skips over any buffers * it can't get a hash_lock on, and so may not catch all candidates. * It may also return without evicting as much space as requested. */ static void * arc_evict(arc_state_t *state, spa_t *spa, int64_t bytes, boolean_t recycle, arc_buf_contents_t type) { arc_state_t *evicted_state; uint64_t bytes_evicted = 0, skipped = 0, missed = 0; arc_buf_hdr_t *ab, *ab_prev = NULL; list_t *list = &state->arcs_list[type]; kmutex_t *hash_lock; boolean_t have_lock; void *stolen = NULL; ASSERT(state == arc_mru || state == arc_mfu); evicted_state = (state == arc_mru) ? arc_mru_ghost : arc_mfu_ghost; mutex_enter(&state->arcs_mtx); mutex_enter(&evicted_state->arcs_mtx); for (ab = list_tail(list); ab; ab = ab_prev) { ab_prev = list_prev(list, ab); /* prefetch buffers have a minimum lifespan */ if (HDR_IO_IN_PROGRESS(ab) || (spa && ab->b_spa != spa) || (ab->b_flags & (ARC_PREFETCH|ARC_INDIRECT) && lbolt - ab->b_arc_access < arc_min_prefetch_lifespan)) { skipped++; continue; } /* "lookahead" for better eviction candidate */ if (recycle && ab->b_size != bytes && ab_prev && ab_prev->b_size == bytes) continue; hash_lock = HDR_LOCK(ab); have_lock = MUTEX_HELD(hash_lock); if (have_lock || mutex_tryenter(hash_lock)) { ASSERT3U(refcount_count(&ab->b_refcnt), ==, 0); ASSERT(ab->b_datacnt > 0); while (ab->b_buf) { arc_buf_t *buf = ab->b_buf; if (!rw_tryenter(&buf->b_lock, RW_WRITER)) { missed += 1; break; } if (buf->b_data) { bytes_evicted += ab->b_size; if (recycle && ab->b_type == type && ab->b_size == bytes && !HDR_L2_WRITING(ab)) { stolen = buf->b_data; recycle = FALSE; } } if (buf->b_efunc) { mutex_enter(&arc_eviction_mtx); arc_buf_destroy(buf, buf->b_data == stolen, FALSE); ab->b_buf = buf->b_next; buf->b_hdr = &arc_eviction_hdr; buf->b_next = arc_eviction_list; arc_eviction_list = buf; mutex_exit(&arc_eviction_mtx); rw_exit(&buf->b_lock); } else { rw_exit(&buf->b_lock); arc_buf_destroy(buf, buf->b_data == stolen, TRUE); } } if (ab->b_datacnt == 0) { arc_change_state(evicted_state, ab, hash_lock); ASSERT(HDR_IN_HASH_TABLE(ab)); ab->b_flags |= ARC_IN_HASH_TABLE; ab->b_flags &= ~ARC_BUF_AVAILABLE; DTRACE_PROBE1(arc__evict, arc_buf_hdr_t *, ab); } if (!have_lock) mutex_exit(hash_lock); if (bytes >= 0 && bytes_evicted >= bytes) break; } else { missed += 1; } } mutex_exit(&evicted_state->arcs_mtx); mutex_exit(&state->arcs_mtx); if (bytes_evicted < bytes) dprintf("only evicted %lld bytes from %x", (longlong_t)bytes_evicted, state); if (skipped) ARCSTAT_INCR(arcstat_evict_skip, skipped); if (missed) ARCSTAT_INCR(arcstat_mutex_miss, missed); /* * We have just evicted some date into the ghost state, make * sure we also adjust the ghost state size if necessary. */ if (arc_no_grow && arc_mru_ghost->arcs_size + arc_mfu_ghost->arcs_size > arc_c) { int64_t mru_over = arc_anon->arcs_size + arc_mru->arcs_size + arc_mru_ghost->arcs_size - arc_c; if (mru_over > 0 && arc_mru_ghost->arcs_lsize[type] > 0) { int64_t todelete = MIN(arc_mru_ghost->arcs_lsize[type], mru_over); arc_evict_ghost(arc_mru_ghost, NULL, todelete); } else if (arc_mfu_ghost->arcs_lsize[type] > 0) { int64_t todelete = MIN(arc_mfu_ghost->arcs_lsize[type], arc_mru_ghost->arcs_size + arc_mfu_ghost->arcs_size - arc_c); arc_evict_ghost(arc_mfu_ghost, NULL, todelete); } } return (stolen); } /* * Remove buffers from list until we've removed the specified number of * bytes. Destroy the buffers that are removed. */ static void arc_evict_ghost(arc_state_t *state, spa_t *spa, int64_t bytes) { arc_buf_hdr_t *ab, *ab_prev; list_t *list = &state->arcs_list[ARC_BUFC_DATA]; kmutex_t *hash_lock; uint64_t bytes_deleted = 0; uint64_t bufs_skipped = 0; ASSERT(GHOST_STATE(state)); top: mutex_enter(&state->arcs_mtx); for (ab = list_tail(list); ab; ab = ab_prev) { ab_prev = list_prev(list, ab); if (spa && ab->b_spa != spa) continue; hash_lock = HDR_LOCK(ab); if (mutex_tryenter(hash_lock)) { ASSERT(!HDR_IO_IN_PROGRESS(ab)); ASSERT(ab->b_buf == NULL); ARCSTAT_BUMP(arcstat_deleted); bytes_deleted += ab->b_size; if (ab->b_l2hdr != NULL) { /* * This buffer is cached on the 2nd Level ARC; * don't destroy the header. */ arc_change_state(arc_l2c_only, ab, hash_lock); mutex_exit(hash_lock); } else { arc_change_state(arc_anon, ab, hash_lock); mutex_exit(hash_lock); arc_hdr_destroy(ab); } DTRACE_PROBE1(arc__delete, arc_buf_hdr_t *, ab); if (bytes >= 0 && bytes_deleted >= bytes) break; } else { if (bytes < 0) { mutex_exit(&state->arcs_mtx); mutex_enter(hash_lock); mutex_exit(hash_lock); goto top; } bufs_skipped += 1; } } mutex_exit(&state->arcs_mtx); if (list == &state->arcs_list[ARC_BUFC_DATA] && (bytes < 0 || bytes_deleted < bytes)) { list = &state->arcs_list[ARC_BUFC_METADATA]; goto top; } if (bufs_skipped) { ARCSTAT_INCR(arcstat_mutex_miss, bufs_skipped); ASSERT(bytes >= 0); } if (bytes_deleted < bytes) dprintf("only deleted %lld bytes from %p", (longlong_t)bytes_deleted, state); } static void arc_adjust(void) { int64_t top_sz, mru_over, arc_over, todelete; top_sz = arc_anon->arcs_size + arc_mru->arcs_size + arc_meta_used; if (top_sz > arc_p && arc_mru->arcs_lsize[ARC_BUFC_DATA] > 0) { int64_t toevict = MIN(arc_mru->arcs_lsize[ARC_BUFC_DATA], top_sz - arc_p); (void) arc_evict(arc_mru, NULL, toevict, FALSE, ARC_BUFC_DATA); top_sz = arc_anon->arcs_size + arc_mru->arcs_size; } if (top_sz > arc_p && arc_mru->arcs_lsize[ARC_BUFC_METADATA] > 0) { int64_t toevict = MIN(arc_mru->arcs_lsize[ARC_BUFC_METADATA], top_sz - arc_p); (void) arc_evict(arc_mru, NULL, toevict, FALSE, ARC_BUFC_METADATA); top_sz = arc_anon->arcs_size + arc_mru->arcs_size; } mru_over = top_sz + arc_mru_ghost->arcs_size - arc_c; if (mru_over > 0) { if (arc_mru_ghost->arcs_size > 0) { todelete = MIN(arc_mru_ghost->arcs_size, mru_over); arc_evict_ghost(arc_mru_ghost, NULL, todelete); } } if ((arc_over = arc_size - arc_c) > 0) { int64_t tbl_over; if (arc_mfu->arcs_lsize[ARC_BUFC_DATA] > 0) { int64_t toevict = MIN(arc_mfu->arcs_lsize[ARC_BUFC_DATA], arc_over); (void) arc_evict(arc_mfu, NULL, toevict, FALSE, ARC_BUFC_DATA); arc_over = arc_size - arc_c; } if (arc_over > 0 && arc_mfu->arcs_lsize[ARC_BUFC_METADATA] > 0) { int64_t toevict = MIN(arc_mfu->arcs_lsize[ARC_BUFC_METADATA], arc_over); (void) arc_evict(arc_mfu, NULL, toevict, FALSE, ARC_BUFC_METADATA); } tbl_over = arc_size + arc_mru_ghost->arcs_size + arc_mfu_ghost->arcs_size - arc_c * 2; if (tbl_over > 0 && arc_mfu_ghost->arcs_size > 0) { todelete = MIN(arc_mfu_ghost->arcs_size, tbl_over); arc_evict_ghost(arc_mfu_ghost, NULL, todelete); } } } static void arc_do_user_evicts(void) { mutex_enter(&arc_eviction_mtx); while (arc_eviction_list != NULL) { arc_buf_t *buf = arc_eviction_list; arc_eviction_list = buf->b_next; rw_enter(&buf->b_lock, RW_WRITER); buf->b_hdr = NULL; rw_exit(&buf->b_lock); mutex_exit(&arc_eviction_mtx); if (buf->b_efunc != NULL) VERIFY(buf->b_efunc(buf) == 0); buf->b_efunc = NULL; buf->b_private = NULL; kmem_cache_free(buf_cache, buf); mutex_enter(&arc_eviction_mtx); } mutex_exit(&arc_eviction_mtx); } /* * Flush all *evictable* data from the cache for the given spa. * NOTE: this will not touch "active" (i.e. referenced) data. */ void arc_flush(spa_t *spa) { while (list_head(&arc_mru->arcs_list[ARC_BUFC_DATA])) { (void) arc_evict(arc_mru, spa, -1, FALSE, ARC_BUFC_DATA); if (spa) break; } while (list_head(&arc_mru->arcs_list[ARC_BUFC_METADATA])) { (void) arc_evict(arc_mru, spa, -1, FALSE, ARC_BUFC_METADATA); if (spa) break; } while (list_head(&arc_mfu->arcs_list[ARC_BUFC_DATA])) { (void) arc_evict(arc_mfu, spa, -1, FALSE, ARC_BUFC_DATA); if (spa) break; } while (list_head(&arc_mfu->arcs_list[ARC_BUFC_METADATA])) { (void) arc_evict(arc_mfu, spa, -1, FALSE, ARC_BUFC_METADATA); if (spa) break; } arc_evict_ghost(arc_mru_ghost, spa, -1); arc_evict_ghost(arc_mfu_ghost, spa, -1); mutex_enter(&arc_reclaim_thr_lock); arc_do_user_evicts(); mutex_exit(&arc_reclaim_thr_lock); ASSERT(spa || arc_eviction_list == NULL); } int arc_shrink_shift = 5; /* log2(fraction of arc to reclaim) */ void arc_shrink(void) { if (arc_c > arc_c_min) { uint64_t to_free; #ifdef _KERNEL to_free = MAX(arc_c >> arc_shrink_shift, ptob(needfree)); #else to_free = arc_c >> arc_shrink_shift; #endif if (arc_c > arc_c_min + to_free) atomic_add_64(&arc_c, -to_free); else arc_c = arc_c_min; atomic_add_64(&arc_p, -(arc_p >> arc_shrink_shift)); if (arc_c > arc_size) arc_c = MAX(arc_size, arc_c_min); if (arc_p > arc_c) arc_p = (arc_c >> 1); ASSERT(arc_c >= arc_c_min); ASSERT((int64_t)arc_p >= 0); } if (arc_size > arc_c) arc_adjust(); } static int arc_reclaim_needed(void) { uint64_t extra; #ifdef _KERNEL if (needfree) return (1); /* * take 'desfree' extra pages, so we reclaim sooner, rather than later */ extra = desfree; /* * check that we're out of range of the pageout scanner. It starts to * schedule paging if freemem is less than lotsfree and needfree. * lotsfree is the high-water mark for pageout, and needfree is the * number of needed free pages. We add extra pages here to make sure * the scanner doesn't start up while we're freeing memory. */ if (freemem < lotsfree + needfree + extra) return (1); /* * check to make sure that swapfs has enough space so that anon * reservations can still succeed. anon_resvmem() checks that the * availrmem is greater than swapfs_minfree, and the number of reserved * swap pages. We also add a bit of extra here just to prevent * circumstances from getting really dire. */ if (availrmem < swapfs_minfree + swapfs_reserve + extra) return (1); #if defined(__i386) /* * If we're on an i386 platform, it's possible that we'll exhaust the * kernel heap space before we ever run out of available physical * memory. Most checks of the size of the heap_area compare against * tune.t_minarmem, which is the minimum available real memory that we * can have in the system. However, this is generally fixed at 25 pages * which is so low that it's useless. In this comparison, we seek to * calculate the total heap-size, and reclaim if more than 3/4ths of the * heap is allocated. (Or, in the calculation, if less than 1/4th is * free) */ if (btop(vmem_size(heap_arena, VMEM_FREE)) < (btop(vmem_size(heap_arena, VMEM_FREE | VMEM_ALLOC)) >> 2)) return (1); #endif #else if (spa_get_random(100) == 0) return (1); #endif return (0); } static void arc_kmem_reap_now(arc_reclaim_strategy_t strat) { size_t i; kmem_cache_t *prev_cache = NULL; kmem_cache_t *prev_data_cache = NULL; extern kmem_cache_t *zio_buf_cache[]; extern kmem_cache_t *zio_data_buf_cache[]; #ifdef _KERNEL if (arc_meta_used >= arc_meta_limit) { /* * We are exceeding our meta-data cache limit. * Purge some DNLC entries to release holds on meta-data. */ dnlc_reduce_cache((void *)(uintptr_t)arc_reduce_dnlc_percent); } #if defined(__i386) /* * Reclaim unused memory from all kmem caches. */ kmem_reap(); #endif #endif /* * An aggressive reclamation will shrink the cache size as well as * reap free buffers from the arc kmem caches. */ if (strat == ARC_RECLAIM_AGGR) arc_shrink(); for (i = 0; i < SPA_MAXBLOCKSIZE >> SPA_MINBLOCKSHIFT; i++) { if (zio_buf_cache[i] != prev_cache) { prev_cache = zio_buf_cache[i]; kmem_cache_reap_now(zio_buf_cache[i]); } if (zio_data_buf_cache[i] != prev_data_cache) { prev_data_cache = zio_data_buf_cache[i]; kmem_cache_reap_now(zio_data_buf_cache[i]); } } kmem_cache_reap_now(buf_cache); kmem_cache_reap_now(hdr_cache); } static void arc_reclaim_thread(void) { clock_t growtime = 0; arc_reclaim_strategy_t last_reclaim = ARC_RECLAIM_CONS; callb_cpr_t cpr; CALLB_CPR_INIT(&cpr, &arc_reclaim_thr_lock, callb_generic_cpr, FTAG); mutex_enter(&arc_reclaim_thr_lock); while (arc_thread_exit == 0) { if (arc_reclaim_needed()) { if (arc_no_grow) { if (last_reclaim == ARC_RECLAIM_CONS) { last_reclaim = ARC_RECLAIM_AGGR; } else { last_reclaim = ARC_RECLAIM_CONS; } } else { arc_no_grow = TRUE; last_reclaim = ARC_RECLAIM_AGGR; membar_producer(); } /* reset the growth delay for every reclaim */ growtime = lbolt + (arc_grow_retry * hz); arc_kmem_reap_now(last_reclaim); arc_warm = B_TRUE; } else if (arc_no_grow && lbolt >= growtime) { arc_no_grow = FALSE; } if (2 * arc_c < arc_size + arc_mru_ghost->arcs_size + arc_mfu_ghost->arcs_size) arc_adjust(); if (arc_eviction_list != NULL) arc_do_user_evicts(); /* block until needed, or one second, whichever is shorter */ CALLB_CPR_SAFE_BEGIN(&cpr); (void) cv_timedwait(&arc_reclaim_thr_cv, &arc_reclaim_thr_lock, (lbolt + hz)); CALLB_CPR_SAFE_END(&cpr, &arc_reclaim_thr_lock); } arc_thread_exit = 0; cv_broadcast(&arc_reclaim_thr_cv); CALLB_CPR_EXIT(&cpr); /* drops arc_reclaim_thr_lock */ thread_exit(); } /* * Adapt arc info given the number of bytes we are trying to add and * the state that we are comming from. This function is only called * when we are adding new content to the cache. */ static void arc_adapt(int bytes, arc_state_t *state) { int mult; if (state == arc_l2c_only) return; ASSERT(bytes > 0); /* * Adapt the target size of the MRU list: * - if we just hit in the MRU ghost list, then increase * the target size of the MRU list. * - if we just hit in the MFU ghost list, then increase * the target size of the MFU list by decreasing the * target size of the MRU list. */ if (state == arc_mru_ghost) { mult = ((arc_mru_ghost->arcs_size >= arc_mfu_ghost->arcs_size) ? 1 : (arc_mfu_ghost->arcs_size/arc_mru_ghost->arcs_size)); arc_p = MIN(arc_c, arc_p + bytes * mult); } else if (state == arc_mfu_ghost) { mult = ((arc_mfu_ghost->arcs_size >= arc_mru_ghost->arcs_size) ? 1 : (arc_mru_ghost->arcs_size/arc_mfu_ghost->arcs_size)); arc_p = MAX(0, (int64_t)arc_p - bytes * mult); } ASSERT((int64_t)arc_p >= 0); if (arc_reclaim_needed()) { cv_signal(&arc_reclaim_thr_cv); return; } if (arc_no_grow) return; if (arc_c >= arc_c_max) return; /* * If we're within (2 * maxblocksize) bytes of the target * cache size, increment the target cache size */ if (arc_size > arc_c - (2ULL << SPA_MAXBLOCKSHIFT)) { atomic_add_64(&arc_c, (int64_t)bytes); if (arc_c > arc_c_max) arc_c = arc_c_max; else if (state == arc_anon) atomic_add_64(&arc_p, (int64_t)bytes); if (arc_p > arc_c) arc_p = arc_c; } ASSERT((int64_t)arc_p >= 0); } /* * Check if the cache has reached its limits and eviction is required * prior to insert. */ static int arc_evict_needed(arc_buf_contents_t type) { if (type == ARC_BUFC_METADATA && arc_meta_used >= arc_meta_limit) return (1); #ifdef _KERNEL /* * If zio data pages are being allocated out of a separate heap segment, * then enforce that the size of available vmem for this area remains * above about 1/32nd free. */ if (type == ARC_BUFC_DATA && zio_arena != NULL && vmem_size(zio_arena, VMEM_FREE) < (vmem_size(zio_arena, VMEM_ALLOC) >> 5)) return (1); #endif if (arc_reclaim_needed()) return (1); return (arc_size > arc_c); } /* * The buffer, supplied as the first argument, needs a data block. * So, if we are at cache max, determine which cache should be victimized. * We have the following cases: * * 1. Insert for MRU, p > sizeof(arc_anon + arc_mru) -> * In this situation if we're out of space, but the resident size of the MFU is * under the limit, victimize the MFU cache to satisfy this insertion request. * * 2. Insert for MRU, p <= sizeof(arc_anon + arc_mru) -> * Here, we've used up all of the available space for the MRU, so we need to * evict from our own cache instead. Evict from the set of resident MRU * entries. * * 3. Insert for MFU (c - p) > sizeof(arc_mfu) -> * c minus p represents the MFU space in the cache, since p is the size of the * cache that is dedicated to the MRU. In this situation there's still space on * the MFU side, so the MRU side needs to be victimized. * * 4. Insert for MFU (c - p) < sizeof(arc_mfu) -> * MFU's resident set is consuming more space than it has been allotted. In * this situation, we must victimize our own cache, the MFU, for this insertion. */ static void arc_get_data_buf(arc_buf_t *buf) { arc_state_t *state = buf->b_hdr->b_state; uint64_t size = buf->b_hdr->b_size; arc_buf_contents_t type = buf->b_hdr->b_type; arc_adapt(size, state); /* * We have not yet reached cache maximum size, * just allocate a new buffer. */ if (!arc_evict_needed(type)) { if (type == ARC_BUFC_METADATA) { buf->b_data = zio_buf_alloc(size); arc_space_consume(size); } else { ASSERT(type == ARC_BUFC_DATA); buf->b_data = zio_data_buf_alloc(size); atomic_add_64(&arc_size, size); } goto out; } /* * If we are prefetching from the mfu ghost list, this buffer * will end up on the mru list; so steal space from there. */ if (state == arc_mfu_ghost) state = buf->b_hdr->b_flags & ARC_PREFETCH ? arc_mru : arc_mfu; else if (state == arc_mru_ghost) state = arc_mru; if (state == arc_mru || state == arc_anon) { uint64_t mru_used = arc_anon->arcs_size + arc_mru->arcs_size; state = (arc_mfu->arcs_lsize[type] > 0 && arc_p > mru_used) ? arc_mfu : arc_mru; } else { /* MFU cases */ uint64_t mfu_space = arc_c - arc_p; state = (arc_mru->arcs_lsize[type] > 0 && mfu_space > arc_mfu->arcs_size) ? arc_mru : arc_mfu; } if ((buf->b_data = arc_evict(state, NULL, size, TRUE, type)) == NULL) { if (type == ARC_BUFC_METADATA) { buf->b_data = zio_buf_alloc(size); arc_space_consume(size); } else { ASSERT(type == ARC_BUFC_DATA); buf->b_data = zio_data_buf_alloc(size); atomic_add_64(&arc_size, size); } ARCSTAT_BUMP(arcstat_recycle_miss); } ASSERT(buf->b_data != NULL); out: /* * Update the state size. Note that ghost states have a * "ghost size" and so don't need to be updated. */ if (!GHOST_STATE(buf->b_hdr->b_state)) { arc_buf_hdr_t *hdr = buf->b_hdr; atomic_add_64(&hdr->b_state->arcs_size, size); if (list_link_active(&hdr->b_arc_node)) { ASSERT(refcount_is_zero(&hdr->b_refcnt)); atomic_add_64(&hdr->b_state->arcs_lsize[type], size); } /* * If we are growing the cache, and we are adding anonymous * data, and we have outgrown arc_p, update arc_p */ if (arc_size < arc_c && hdr->b_state == arc_anon && arc_anon->arcs_size + arc_mru->arcs_size > arc_p) arc_p = MIN(arc_c, arc_p + size); } } /* * This routine is called whenever a buffer is accessed. * NOTE: the hash lock is dropped in this function. */ static void arc_access(arc_buf_hdr_t *buf, kmutex_t *hash_lock) { ASSERT(MUTEX_HELD(hash_lock)); if (buf->b_state == arc_anon) { /* * This buffer is not in the cache, and does not * appear in our "ghost" list. Add the new buffer * to the MRU state. */ ASSERT(buf->b_arc_access == 0); buf->b_arc_access = lbolt; DTRACE_PROBE1(new_state__mru, arc_buf_hdr_t *, buf); arc_change_state(arc_mru, buf, hash_lock); } else if (buf->b_state == arc_mru) { /* * If this buffer is here because of a prefetch, then either: * - clear the flag if this is a "referencing" read * (any subsequent access will bump this into the MFU state). * or * - move the buffer to the head of the list if this is * another prefetch (to make it less likely to be evicted). */ if ((buf->b_flags & ARC_PREFETCH) != 0) { if (refcount_count(&buf->b_refcnt) == 0) { ASSERT(list_link_active(&buf->b_arc_node)); } else { buf->b_flags &= ~ARC_PREFETCH; ARCSTAT_BUMP(arcstat_mru_hits); } buf->b_arc_access = lbolt; return; } /* * This buffer has been "accessed" only once so far, * but it is still in the cache. Move it to the MFU * state. */ if (lbolt > buf->b_arc_access + ARC_MINTIME) { /* * More than 125ms have passed since we * instantiated this buffer. Move it to the * most frequently used state. */ buf->b_arc_access = lbolt; DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, buf); arc_change_state(arc_mfu, buf, hash_lock); } ARCSTAT_BUMP(arcstat_mru_hits); } else if (buf->b_state == arc_mru_ghost) { arc_state_t *new_state; /* * This buffer has been "accessed" recently, but * was evicted from the cache. Move it to the * MFU state. */ if (buf->b_flags & ARC_PREFETCH) { new_state = arc_mru; if (refcount_count(&buf->b_refcnt) > 0) buf->b_flags &= ~ARC_PREFETCH; DTRACE_PROBE1(new_state__mru, arc_buf_hdr_t *, buf); } else { new_state = arc_mfu; DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, buf); } buf->b_arc_access = lbolt; arc_change_state(new_state, buf, hash_lock); ARCSTAT_BUMP(arcstat_mru_ghost_hits); } else if (buf->b_state == arc_mfu) { /* * This buffer has been accessed more than once and is * still in the cache. Keep it in the MFU state. * * NOTE: an add_reference() that occurred when we did * the arc_read() will have kicked this off the list. * If it was a prefetch, we will explicitly move it to * the head of the list now. */ if ((buf->b_flags & ARC_PREFETCH) != 0) { ASSERT(refcount_count(&buf->b_refcnt) == 0); ASSERT(list_link_active(&buf->b_arc_node)); } ARCSTAT_BUMP(arcstat_mfu_hits); buf->b_arc_access = lbolt; } else if (buf->b_state == arc_mfu_ghost) { arc_state_t *new_state = arc_mfu; /* * This buffer has been accessed more than once but has * been evicted from the cache. Move it back to the * MFU state. */ if (buf->b_flags & ARC_PREFETCH) { /* * This is a prefetch access... * move this block back to the MRU state. */ ASSERT3U(refcount_count(&buf->b_refcnt), ==, 0); new_state = arc_mru; } buf->b_arc_access = lbolt; DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, buf); arc_change_state(new_state, buf, hash_lock); ARCSTAT_BUMP(arcstat_mfu_ghost_hits); } else if (buf->b_state == arc_l2c_only) { /* * This buffer is on the 2nd Level ARC. */ buf->b_arc_access = lbolt; DTRACE_PROBE1(new_state__mfu, arc_buf_hdr_t *, buf); arc_change_state(arc_mfu, buf, hash_lock); } else { ASSERT(!"invalid arc state"); } } /* a generic arc_done_func_t which you can use */ /* ARGSUSED */ void arc_bcopy_func(zio_t *zio, arc_buf_t *buf, void *arg) { bcopy(buf->b_data, arg, buf->b_hdr->b_size); VERIFY(arc_buf_remove_ref(buf, arg) == 1); } /* a generic arc_done_func_t */ void arc_getbuf_func(zio_t *zio, arc_buf_t *buf, void *arg) { arc_buf_t **bufp = arg; if (zio && zio->io_error) { VERIFY(arc_buf_remove_ref(buf, arg) == 1); *bufp = NULL; } else { *bufp = buf; } } static void arc_read_done(zio_t *zio) { arc_buf_hdr_t *hdr, *found; arc_buf_t *buf; arc_buf_t *abuf; /* buffer we're assigning to callback */ kmutex_t *hash_lock; arc_callback_t *callback_list, *acb; int freeable = FALSE; buf = zio->io_private; hdr = buf->b_hdr; /* * The hdr was inserted into hash-table and removed from lists * prior to starting I/O. We should find this header, since * it's in the hash table, and it should be legit since it's * not possible to evict it during the I/O. The only possible * reason for it not to be found is if we were freed during the * read. */ found = buf_hash_find(zio->io_spa, &hdr->b_dva, hdr->b_birth, &hash_lock); ASSERT((found == NULL && HDR_FREED_IN_READ(hdr) && hash_lock == NULL) || (found == hdr && DVA_EQUAL(&hdr->b_dva, BP_IDENTITY(zio->io_bp))) || (found == hdr && HDR_L2_READING(hdr))); hdr->b_flags &= ~ARC_L2_EVICTED; if (l2arc_noprefetch && (hdr->b_flags & ARC_PREFETCH)) hdr->b_flags &= ~ARC_L2CACHE; /* byteswap if necessary */ callback_list = hdr->b_acb; ASSERT(callback_list != NULL); if (BP_SHOULD_BYTESWAP(zio->io_bp)) { arc_byteswap_func_t *func = BP_GET_LEVEL(zio->io_bp) > 0 ? byteswap_uint64_array : dmu_ot[BP_GET_TYPE(zio->io_bp)].ot_byteswap; func(buf->b_data, hdr->b_size); } arc_cksum_compute(buf, B_FALSE); /* create copies of the data buffer for the callers */ abuf = buf; for (acb = callback_list; acb; acb = acb->acb_next) { if (acb->acb_done) { if (abuf == NULL) abuf = arc_buf_clone(buf); acb->acb_buf = abuf; abuf = NULL; } } hdr->b_acb = NULL; hdr->b_flags &= ~ARC_IO_IN_PROGRESS; ASSERT(!HDR_BUF_AVAILABLE(hdr)); if (abuf == buf) hdr->b_flags |= ARC_BUF_AVAILABLE; ASSERT(refcount_is_zero(&hdr->b_refcnt) || callback_list != NULL); if (zio->io_error != 0) { hdr->b_flags |= ARC_IO_ERROR; if (hdr->b_state != arc_anon) arc_change_state(arc_anon, hdr, hash_lock); if (HDR_IN_HASH_TABLE(hdr)) buf_hash_remove(hdr); freeable = refcount_is_zero(&hdr->b_refcnt); } /* * Broadcast before we drop the hash_lock to avoid the possibility * that the hdr (and hence the cv) might be freed before we get to * the cv_broadcast(). */ cv_broadcast(&hdr->b_cv); if (hash_lock) { /* * Only call arc_access on anonymous buffers. This is because * if we've issued an I/O for an evicted buffer, we've already * called arc_access (to prevent any simultaneous readers from * getting confused). */ if (zio->io_error == 0 && hdr->b_state == arc_anon) arc_access(hdr, hash_lock); mutex_exit(hash_lock); } else { /* * This block was freed while we waited for the read to * complete. It has been removed from the hash table and * moved to the anonymous state (so that it won't show up * in the cache). */ ASSERT3P(hdr->b_state, ==, arc_anon); freeable = refcount_is_zero(&hdr->b_refcnt); } /* execute each callback and free its structure */ while ((acb = callback_list) != NULL) { if (acb->acb_done) acb->acb_done(zio, acb->acb_buf, acb->acb_private); if (acb->acb_zio_dummy != NULL) { acb->acb_zio_dummy->io_error = zio->io_error; zio_nowait(acb->acb_zio_dummy); } callback_list = acb->acb_next; kmem_free(acb, sizeof (arc_callback_t)); } if (freeable) arc_hdr_destroy(hdr); } /* * "Read" the block block at the specified DVA (in bp) via the * cache. If the block is found in the cache, invoke the provided * callback immediately and return. Note that the `zio' parameter * in the callback will be NULL in this case, since no IO was * required. If the block is not in the cache pass the read request * on to the spa with a substitute callback function, so that the * requested block will be added to the cache. * * If a read request arrives for a block that has a read in-progress, * either wait for the in-progress read to complete (and return the * results); or, if this is a read with a "done" func, add a record * to the read to invoke the "done" func when the read completes, * and return; or just return. * * arc_read_done() will invoke all the requested "done" functions * for readers of this block. * * Normal callers should use arc_read and pass the arc buffer and offset * for the bp. But if you know you don't need locking, you can use * arc_read_bp. */ int arc_read(zio_t *pio, spa_t *spa, blkptr_t *bp, arc_buf_t *pbuf, arc_done_func_t *done, void *private, int priority, int zio_flags, uint32_t *arc_flags, const zbookmark_t *zb) { int err; arc_buf_hdr_t *hdr = pbuf->b_hdr; ASSERT(!refcount_is_zero(&pbuf->b_hdr->b_refcnt)); ASSERT3U((char *)bp - (char *)pbuf->b_data, <, pbuf->b_hdr->b_size); rw_enter(&pbuf->b_lock, RW_READER); err = arc_read_nolock(pio, spa, bp, done, private, priority, zio_flags, arc_flags, zb); ASSERT3P(hdr, ==, pbuf->b_hdr); rw_exit(&pbuf->b_lock); return (err); } int arc_read_nolock(zio_t *pio, spa_t *spa, blkptr_t *bp, arc_done_func_t *done, void *private, int priority, int zio_flags, uint32_t *arc_flags, const zbookmark_t *zb) { arc_buf_hdr_t *hdr; arc_buf_t *buf; kmutex_t *hash_lock; zio_t *rzio; top: hdr = buf_hash_find(spa, BP_IDENTITY(bp), bp->blk_birth, &hash_lock); if (hdr && hdr->b_datacnt > 0) { *arc_flags |= ARC_CACHED; if (HDR_IO_IN_PROGRESS(hdr)) { if (*arc_flags & ARC_WAIT) { cv_wait(&hdr->b_cv, hash_lock); mutex_exit(hash_lock); goto top; } ASSERT(*arc_flags & ARC_NOWAIT); if (done) { arc_callback_t *acb = NULL; acb = kmem_zalloc(sizeof (arc_callback_t), KM_SLEEP); acb->acb_done = done; acb->acb_private = private; if (pio != NULL) acb->acb_zio_dummy = zio_null(pio, spa, NULL, NULL, zio_flags); ASSERT(acb->acb_done != NULL); acb->acb_next = hdr->b_acb; hdr->b_acb = acb; add_reference(hdr, hash_lock, private); mutex_exit(hash_lock); return (0); } mutex_exit(hash_lock); return (0); } ASSERT(hdr->b_state == arc_mru || hdr->b_state == arc_mfu); if (done) { add_reference(hdr, hash_lock, private); /* * If this block is already in use, create a new * copy of the data so that we will be guaranteed * that arc_release() will always succeed. */ buf = hdr->b_buf; ASSERT(buf); ASSERT(buf->b_data); if (HDR_BUF_AVAILABLE(hdr)) { ASSERT(buf->b_efunc == NULL); hdr->b_flags &= ~ARC_BUF_AVAILABLE; } else { buf = arc_buf_clone(buf); } } else if (*arc_flags & ARC_PREFETCH && refcount_count(&hdr->b_refcnt) == 0) { hdr->b_flags |= ARC_PREFETCH; } DTRACE_PROBE1(arc__hit, arc_buf_hdr_t *, hdr); arc_access(hdr, hash_lock); if (*arc_flags & ARC_L2CACHE) hdr->b_flags |= ARC_L2CACHE; mutex_exit(hash_lock); ARCSTAT_BUMP(arcstat_hits); ARCSTAT_CONDSTAT(!(hdr->b_flags & ARC_PREFETCH), demand, prefetch, hdr->b_type != ARC_BUFC_METADATA, data, metadata, hits); if (done) done(NULL, buf, private); } else { uint64_t size = BP_GET_LSIZE(bp); arc_callback_t *acb; vdev_t *vd = NULL; daddr_t addr; if (hdr == NULL) { /* this block is not in the cache */ arc_buf_hdr_t *exists; arc_buf_contents_t type = BP_GET_BUFC_TYPE(bp); buf = arc_buf_alloc(spa, size, private, type); hdr = buf->b_hdr; hdr->b_dva = *BP_IDENTITY(bp); hdr->b_birth = bp->blk_birth; hdr->b_cksum0 = bp->blk_cksum.zc_word[0]; exists = buf_hash_insert(hdr, &hash_lock); if (exists) { /* somebody beat us to the hash insert */ mutex_exit(hash_lock); bzero(&hdr->b_dva, sizeof (dva_t)); hdr->b_birth = 0; hdr->b_cksum0 = 0; (void) arc_buf_remove_ref(buf, private); goto top; /* restart the IO request */ } /* if this is a prefetch, we don't have a reference */ if (*arc_flags & ARC_PREFETCH) { (void) remove_reference(hdr, hash_lock, private); hdr->b_flags |= ARC_PREFETCH; } if (*arc_flags & ARC_L2CACHE) hdr->b_flags |= ARC_L2CACHE; if (BP_GET_LEVEL(bp) > 0) hdr->b_flags |= ARC_INDIRECT; } else { /* this block is in the ghost cache */ ASSERT(GHOST_STATE(hdr->b_state)); ASSERT(!HDR_IO_IN_PROGRESS(hdr)); ASSERT3U(refcount_count(&hdr->b_refcnt), ==, 0); ASSERT(hdr->b_buf == NULL); /* if this is a prefetch, we don't have a reference */ if (*arc_flags & ARC_PREFETCH) hdr->b_flags |= ARC_PREFETCH; else add_reference(hdr, hash_lock, private); if (*arc_flags & ARC_L2CACHE) hdr->b_flags |= ARC_L2CACHE; buf = kmem_cache_alloc(buf_cache, KM_PUSHPAGE); buf->b_hdr = hdr; buf->b_data = NULL; buf->b_efunc = NULL; buf->b_private = NULL; buf->b_next = NULL; hdr->b_buf = buf; arc_get_data_buf(buf); ASSERT(hdr->b_datacnt == 0); hdr->b_datacnt = 1; } acb = kmem_zalloc(sizeof (arc_callback_t), KM_SLEEP); acb->acb_done = done; acb->acb_private = private; ASSERT(hdr->b_acb == NULL); hdr->b_acb = acb; hdr->b_flags |= ARC_IO_IN_PROGRESS; /* * If the buffer has been evicted, migrate it to a present state * before issuing the I/O. Once we drop the hash-table lock, * the header will be marked as I/O in progress and have an * attached buffer. At this point, anybody who finds this * buffer ought to notice that it's legit but has a pending I/O. */ if (GHOST_STATE(hdr->b_state)) arc_access(hdr, hash_lock); if (HDR_L2CACHE(hdr) && hdr->b_l2hdr != NULL && (vd = hdr->b_l2hdr->b_dev->l2ad_vdev) != NULL) { addr = hdr->b_l2hdr->b_daddr; /* * Lock out device removal. */ if (vdev_is_dead(vd) || !spa_config_tryenter(spa, SCL_L2ARC, vd, RW_READER)) vd = NULL; } mutex_exit(hash_lock); ASSERT3U(hdr->b_size, ==, size); DTRACE_PROBE3(arc__miss, blkptr_t *, bp, uint64_t, size, zbookmark_t *, zb); ARCSTAT_BUMP(arcstat_misses); ARCSTAT_CONDSTAT(!(hdr->b_flags & ARC_PREFETCH), demand, prefetch, hdr->b_type != ARC_BUFC_METADATA, data, metadata, misses); if (vd != NULL) { /* * Read from the L2ARC if the following are true: * 1. The L2ARC vdev was previously cached. * 2. This buffer still has L2ARC metadata. * 3. This buffer isn't currently writing to the L2ARC. * 4. The L2ARC entry wasn't evicted, which may * also have invalidated the vdev. */ if (hdr->b_l2hdr != NULL && !HDR_L2_WRITING(hdr) && !HDR_L2_EVICTED(hdr)) { l2arc_read_callback_t *cb; DTRACE_PROBE1(l2arc__hit, arc_buf_hdr_t *, hdr); ARCSTAT_BUMP(arcstat_l2_hits); cb = kmem_zalloc(sizeof (l2arc_read_callback_t), KM_SLEEP); cb->l2rcb_buf = buf; cb->l2rcb_spa = spa; cb->l2rcb_bp = *bp; cb->l2rcb_zb = *zb; cb->l2rcb_flags = zio_flags; /* * l2arc read. The SCL_L2ARC lock will be * released by l2arc_read_done(). */ rzio = zio_read_phys(pio, vd, addr, size, buf->b_data, ZIO_CHECKSUM_OFF, l2arc_read_done, cb, priority, zio_flags | ZIO_FLAG_DONT_CACHE | ZIO_FLAG_CANFAIL | ZIO_FLAG_DONT_PROPAGATE | ZIO_FLAG_DONT_RETRY, B_FALSE); DTRACE_PROBE2(l2arc__read, vdev_t *, vd, zio_t *, rzio); if (*arc_flags & ARC_NOWAIT) { zio_nowait(rzio); return (0); } ASSERT(*arc_flags & ARC_WAIT); if (zio_wait(rzio) == 0) return (0); /* l2arc read error; goto zio_read() */ } else { DTRACE_PROBE1(l2arc__miss, arc_buf_hdr_t *, hdr); ARCSTAT_BUMP(arcstat_l2_misses); if (HDR_L2_WRITING(hdr)) ARCSTAT_BUMP(arcstat_l2_rw_clash); spa_config_exit(spa, SCL_L2ARC, vd); } } rzio = zio_read(pio, spa, bp, buf->b_data, size, arc_read_done, buf, priority, zio_flags, zb); if (*arc_flags & ARC_WAIT) return (zio_wait(rzio)); ASSERT(*arc_flags & ARC_NOWAIT); zio_nowait(rzio); } return (0); } /* * arc_read() variant to support pool traversal. If the block is already * in the ARC, make a copy of it; otherwise, the caller will do the I/O. * The idea is that we don't want pool traversal filling up memory, but * if the ARC already has the data anyway, we shouldn't pay for the I/O. */ int arc_tryread(spa_t *spa, blkptr_t *bp, void *data) { arc_buf_hdr_t *hdr; kmutex_t *hash_mtx; int rc = 0; hdr = buf_hash_find(spa, BP_IDENTITY(bp), bp->blk_birth, &hash_mtx); if (hdr && hdr->b_datacnt > 0 && !HDR_IO_IN_PROGRESS(hdr)) { arc_buf_t *buf = hdr->b_buf; ASSERT(buf); while (buf->b_data == NULL) { buf = buf->b_next; ASSERT(buf); } bcopy(buf->b_data, data, hdr->b_size); } else { rc = ENOENT; } if (hash_mtx) mutex_exit(hash_mtx); return (rc); } void arc_set_callback(arc_buf_t *buf, arc_evict_func_t *func, void *private) { ASSERT(buf->b_hdr != NULL); ASSERT(buf->b_hdr->b_state != arc_anon); ASSERT(!refcount_is_zero(&buf->b_hdr->b_refcnt) || func == NULL); buf->b_efunc = func; buf->b_private = private; } /* * This is used by the DMU to let the ARC know that a buffer is * being evicted, so the ARC should clean up. If this arc buf * is not yet in the evicted state, it will be put there. */ int arc_buf_evict(arc_buf_t *buf) { arc_buf_hdr_t *hdr; kmutex_t *hash_lock; arc_buf_t **bufp; rw_enter(&buf->b_lock, RW_WRITER); hdr = buf->b_hdr; if (hdr == NULL) { /* * We are in arc_do_user_evicts(). */ ASSERT(buf->b_data == NULL); rw_exit(&buf->b_lock); return (0); } else if (buf->b_data == NULL) { arc_buf_t copy = *buf; /* structure assignment */ /* * We are on the eviction list; process this buffer now * but let arc_do_user_evicts() do the reaping. */ buf->b_efunc = NULL; rw_exit(&buf->b_lock); VERIFY(copy.b_efunc(©) == 0); return (1); } hash_lock = HDR_LOCK(hdr); mutex_enter(hash_lock); ASSERT(buf->b_hdr == hdr); ASSERT3U(refcount_count(&hdr->b_refcnt), <, hdr->b_datacnt); ASSERT(hdr->b_state == arc_mru || hdr->b_state == arc_mfu); /* * Pull this buffer off of the hdr */ bufp = &hdr->b_buf; while (*bufp != buf) bufp = &(*bufp)->b_next; *bufp = buf->b_next; ASSERT(buf->b_data != NULL); arc_buf_destroy(buf, FALSE, FALSE); if (hdr->b_datacnt == 0) { arc_state_t *old_state = hdr->b_state; arc_state_t *evicted_state; ASSERT(refcount_is_zero(&hdr->b_refcnt)); evicted_state = (old_state == arc_mru) ? arc_mru_ghost : arc_mfu_ghost; mutex_enter(&old_state->arcs_mtx); mutex_enter(&evicted_state->arcs_mtx); arc_change_state(evicted_state, hdr, hash_lock); ASSERT(HDR_IN_HASH_TABLE(hdr)); hdr->b_flags |= ARC_IN_HASH_TABLE; hdr->b_flags &= ~ARC_BUF_AVAILABLE; mutex_exit(&evicted_state->arcs_mtx); mutex_exit(&old_state->arcs_mtx); } mutex_exit(hash_lock); rw_exit(&buf->b_lock); VERIFY(buf->b_efunc(buf) == 0); buf->b_efunc = NULL; buf->b_private = NULL; buf->b_hdr = NULL; kmem_cache_free(buf_cache, buf); return (1); } /* * Release this buffer from the cache. This must be done * after a read and prior to modifying the buffer contents. * If the buffer has more than one reference, we must make * a new hdr for the buffer. */ void arc_release(arc_buf_t *buf, void *tag) { arc_buf_hdr_t *hdr; kmutex_t *hash_lock; l2arc_buf_hdr_t *l2hdr; uint64_t buf_size; rw_enter(&buf->b_lock, RW_WRITER); hdr = buf->b_hdr; /* this buffer is not on any list */ ASSERT(refcount_count(&hdr->b_refcnt) > 0); ASSERT(!(hdr->b_flags & ARC_STORED)); if (hdr->b_state == arc_anon) { /* this buffer is already released */ ASSERT3U(refcount_count(&hdr->b_refcnt), ==, 1); ASSERT(BUF_EMPTY(hdr)); ASSERT(buf->b_efunc == NULL); arc_buf_thaw(buf); rw_exit(&buf->b_lock); return; } hash_lock = HDR_LOCK(hdr); mutex_enter(hash_lock); l2hdr = hdr->b_l2hdr; if (l2hdr) { mutex_enter(&l2arc_buflist_mtx); hdr->b_l2hdr = NULL; buf_size = hdr->b_size; } /* * Do we have more than one buf? */ if (hdr->b_datacnt > 1) { arc_buf_hdr_t *nhdr; arc_buf_t **bufp; uint64_t blksz = hdr->b_size; spa_t *spa = hdr->b_spa; arc_buf_contents_t type = hdr->b_type; uint32_t flags = hdr->b_flags; ASSERT(hdr->b_buf != buf || buf->b_next != NULL); /* * Pull the data off of this buf and attach it to * a new anonymous buf. */ (void) remove_reference(hdr, hash_lock, tag); bufp = &hdr->b_buf; while (*bufp != buf) bufp = &(*bufp)->b_next; *bufp = (*bufp)->b_next; buf->b_next = NULL; ASSERT3U(hdr->b_state->arcs_size, >=, hdr->b_size); atomic_add_64(&hdr->b_state->arcs_size, -hdr->b_size); if (refcount_is_zero(&hdr->b_refcnt)) { uint64_t *size = &hdr->b_state->arcs_lsize[hdr->b_type]; ASSERT3U(*size, >=, hdr->b_size); atomic_add_64(size, -hdr->b_size); } hdr->b_datacnt -= 1; arc_cksum_verify(buf); mutex_exit(hash_lock); nhdr = kmem_cache_alloc(hdr_cache, KM_PUSHPAGE); nhdr->b_size = blksz; nhdr->b_spa = spa; nhdr->b_type = type; nhdr->b_buf = buf; nhdr->b_state = arc_anon; nhdr->b_arc_access = 0; nhdr->b_flags = flags & ARC_L2_WRITING; nhdr->b_l2hdr = NULL; nhdr->b_datacnt = 1; nhdr->b_freeze_cksum = NULL; (void) refcount_add(&nhdr->b_refcnt, tag); buf->b_hdr = nhdr; rw_exit(&buf->b_lock); atomic_add_64(&arc_anon->arcs_size, blksz); } else { rw_exit(&buf->b_lock); ASSERT(refcount_count(&hdr->b_refcnt) == 1); ASSERT(!list_link_active(&hdr->b_arc_node)); ASSERT(!HDR_IO_IN_PROGRESS(hdr)); arc_change_state(arc_anon, hdr, hash_lock); hdr->b_arc_access = 0; mutex_exit(hash_lock); bzero(&hdr->b_dva, sizeof (dva_t)); hdr->b_birth = 0; hdr->b_cksum0 = 0; arc_buf_thaw(buf); } buf->b_efunc = NULL; buf->b_private = NULL; if (l2hdr) { list_remove(l2hdr->b_dev->l2ad_buflist, hdr); kmem_free(l2hdr, sizeof (l2arc_buf_hdr_t)); ARCSTAT_INCR(arcstat_l2_size, -buf_size); mutex_exit(&l2arc_buflist_mtx); } } int arc_released(arc_buf_t *buf) { int released; rw_enter(&buf->b_lock, RW_READER); released = (buf->b_data != NULL && buf->b_hdr->b_state == arc_anon); rw_exit(&buf->b_lock); return (released); } int arc_has_callback(arc_buf_t *buf) { int callback; rw_enter(&buf->b_lock, RW_READER); callback = (buf->b_efunc != NULL); rw_exit(&buf->b_lock); return (callback); } #ifdef ZFS_DEBUG int arc_referenced(arc_buf_t *buf) { int referenced; rw_enter(&buf->b_lock, RW_READER); referenced = (refcount_count(&buf->b_hdr->b_refcnt)); rw_exit(&buf->b_lock); return (referenced); } #endif static void arc_write_ready(zio_t *zio) { arc_write_callback_t *callback = zio->io_private; arc_buf_t *buf = callback->awcb_buf; arc_buf_hdr_t *hdr = buf->b_hdr; ASSERT(!refcount_is_zero(&buf->b_hdr->b_refcnt)); callback->awcb_ready(zio, buf, callback->awcb_private); /* * If the IO is already in progress, then this is a re-write * attempt, so we need to thaw and re-compute the cksum. * It is the responsibility of the callback to handle the * accounting for any re-write attempt. */ if (HDR_IO_IN_PROGRESS(hdr)) { mutex_enter(&hdr->b_freeze_lock); if (hdr->b_freeze_cksum != NULL) { kmem_free(hdr->b_freeze_cksum, sizeof (zio_cksum_t)); hdr->b_freeze_cksum = NULL; } mutex_exit(&hdr->b_freeze_lock); } arc_cksum_compute(buf, B_FALSE); hdr->b_flags |= ARC_IO_IN_PROGRESS; } static void arc_write_done(zio_t *zio) { arc_write_callback_t *callback = zio->io_private; arc_buf_t *buf = callback->awcb_buf; arc_buf_hdr_t *hdr = buf->b_hdr; hdr->b_acb = NULL; hdr->b_dva = *BP_IDENTITY(zio->io_bp); hdr->b_birth = zio->io_bp->blk_birth; hdr->b_cksum0 = zio->io_bp->blk_cksum.zc_word[0]; /* * If the block to be written was all-zero, we may have * compressed it away. In this case no write was performed * so there will be no dva/birth-date/checksum. The buffer * must therefor remain anonymous (and uncached). */ if (!BUF_EMPTY(hdr)) { arc_buf_hdr_t *exists; kmutex_t *hash_lock; arc_cksum_verify(buf); exists = buf_hash_insert(hdr, &hash_lock); if (exists) { /* * This can only happen if we overwrite for * sync-to-convergence, because we remove * buffers from the hash table when we arc_free(). */ ASSERT(zio->io_flags & ZIO_FLAG_IO_REWRITE); ASSERT(DVA_EQUAL(BP_IDENTITY(&zio->io_bp_orig), BP_IDENTITY(zio->io_bp))); ASSERT3U(zio->io_bp_orig.blk_birth, ==, zio->io_bp->blk_birth); ASSERT(refcount_is_zero(&exists->b_refcnt)); arc_change_state(arc_anon, exists, hash_lock); mutex_exit(hash_lock); arc_hdr_destroy(exists); exists = buf_hash_insert(hdr, &hash_lock); ASSERT3P(exists, ==, NULL); } hdr->b_flags &= ~ARC_IO_IN_PROGRESS; /* if it's not anon, we are doing a scrub */ if (hdr->b_state == arc_anon) arc_access(hdr, hash_lock); mutex_exit(hash_lock); } else if (callback->awcb_done == NULL) { int destroy_hdr; /* * This is an anonymous buffer with no user callback, * destroy it if there are no active references. */ mutex_enter(&arc_eviction_mtx); destroy_hdr = refcount_is_zero(&hdr->b_refcnt); hdr->b_flags &= ~ARC_IO_IN_PROGRESS; mutex_exit(&arc_eviction_mtx); if (destroy_hdr) arc_hdr_destroy(hdr); } else { hdr->b_flags &= ~ARC_IO_IN_PROGRESS; } hdr->b_flags &= ~ARC_STORED; if (callback->awcb_done) { ASSERT(!refcount_is_zero(&hdr->b_refcnt)); callback->awcb_done(zio, buf, callback->awcb_private); } kmem_free(callback, sizeof (arc_write_callback_t)); } void write_policy(spa_t *spa, const writeprops_t *wp, zio_prop_t *zp) { boolean_t ismd = (wp->wp_level > 0 || dmu_ot[wp->wp_type].ot_metadata); /* Determine checksum setting */ if (ismd) { /* * Metadata always gets checksummed. If the data * checksum is multi-bit correctable, and it's not a * ZBT-style checksum, then it's suitable for metadata * as well. Otherwise, the metadata checksum defaults * to fletcher4. */ if (zio_checksum_table[wp->wp_oschecksum].ci_correctable && !zio_checksum_table[wp->wp_oschecksum].ci_zbt) zp->zp_checksum = wp->wp_oschecksum; else zp->zp_checksum = ZIO_CHECKSUM_FLETCHER_4; } else { zp->zp_checksum = zio_checksum_select(wp->wp_dnchecksum, wp->wp_oschecksum); } /* Determine compression setting */ if (ismd) { /* * XXX -- we should design a compression algorithm * that specializes in arrays of bps. */ zp->zp_compress = zfs_mdcomp_disable ? ZIO_COMPRESS_EMPTY : ZIO_COMPRESS_LZJB; } else { zp->zp_compress = zio_compress_select(wp->wp_dncompress, wp->wp_oscompress); } zp->zp_type = wp->wp_type; zp->zp_level = wp->wp_level; zp->zp_ndvas = MIN(wp->wp_copies + ismd, spa_max_replication(spa)); } zio_t * arc_write(zio_t *pio, spa_t *spa, const writeprops_t *wp, boolean_t l2arc, uint64_t txg, blkptr_t *bp, arc_buf_t *buf, arc_done_func_t *ready, arc_done_func_t *done, void *private, int priority, int zio_flags, const zbookmark_t *zb) { arc_buf_hdr_t *hdr = buf->b_hdr; arc_write_callback_t *callback; zio_t *zio; zio_prop_t zp; ASSERT(ready != NULL); ASSERT(!HDR_IO_ERROR(hdr)); ASSERT((hdr->b_flags & ARC_IO_IN_PROGRESS) == 0); ASSERT(hdr->b_acb == 0); if (l2arc) hdr->b_flags |= ARC_L2CACHE; callback = kmem_zalloc(sizeof (arc_write_callback_t), KM_SLEEP); callback->awcb_ready = ready; callback->awcb_done = done; callback->awcb_private = private; callback->awcb_buf = buf; write_policy(spa, wp, &zp); zio = zio_write(pio, spa, txg, bp, buf->b_data, hdr->b_size, &zp, arc_write_ready, arc_write_done, callback, priority, zio_flags, zb); return (zio); } int arc_free(zio_t *pio, spa_t *spa, uint64_t txg, blkptr_t *bp, zio_done_func_t *done, void *private, uint32_t arc_flags) { arc_buf_hdr_t *ab; kmutex_t *hash_lock; zio_t *zio; /* * If this buffer is in the cache, release it, so it * can be re-used. */ ab = buf_hash_find(spa, BP_IDENTITY(bp), bp->blk_birth, &hash_lock); if (ab != NULL) { /* * The checksum of blocks to free is not always * preserved (eg. on the deadlist). However, if it is * nonzero, it should match what we have in the cache. */ ASSERT(bp->blk_cksum.zc_word[0] == 0 || bp->blk_cksum.zc_word[0] == ab->b_cksum0 || bp->blk_fill == BLK_FILL_ALREADY_FREED); if (ab->b_state != arc_anon) arc_change_state(arc_anon, ab, hash_lock); if (HDR_IO_IN_PROGRESS(ab)) { /* * This should only happen when we prefetch. */ ASSERT(ab->b_flags & ARC_PREFETCH); ASSERT3U(ab->b_datacnt, ==, 1); ab->b_flags |= ARC_FREED_IN_READ; if (HDR_IN_HASH_TABLE(ab)) buf_hash_remove(ab); ab->b_arc_access = 0; bzero(&ab->b_dva, sizeof (dva_t)); ab->b_birth = 0; ab->b_cksum0 = 0; ab->b_buf->b_efunc = NULL; ab->b_buf->b_private = NULL; mutex_exit(hash_lock); } else if (refcount_is_zero(&ab->b_refcnt)) { ab->b_flags |= ARC_FREE_IN_PROGRESS; mutex_exit(hash_lock); arc_hdr_destroy(ab); ARCSTAT_BUMP(arcstat_deleted); } else { /* * We still have an active reference on this * buffer. This can happen, e.g., from * dbuf_unoverride(). */ ASSERT(!HDR_IN_HASH_TABLE(ab)); ab->b_arc_access = 0; bzero(&ab->b_dva, sizeof (dva_t)); ab->b_birth = 0; ab->b_cksum0 = 0; ab->b_buf->b_efunc = NULL; ab->b_buf->b_private = NULL; mutex_exit(hash_lock); } } zio = zio_free(pio, spa, txg, bp, done, private, ZIO_FLAG_MUSTSUCCEED); if (arc_flags & ARC_WAIT) return (zio_wait(zio)); ASSERT(arc_flags & ARC_NOWAIT); zio_nowait(zio); return (0); } static int arc_memory_throttle(uint64_t reserve, uint64_t txg) { #ifdef _KERNEL uint64_t inflight_data = arc_anon->arcs_size; uint64_t available_memory = ptob(freemem); static uint64_t page_load = 0; static uint64_t last_txg = 0; #if defined(__i386) available_memory = MIN(available_memory, vmem_size(heap_arena, VMEM_FREE)); #endif if (available_memory >= zfs_write_limit_max) return (0); if (txg > last_txg) { last_txg = txg; page_load = 0; } /* * If we are in pageout, we know that memory is already tight, * the arc is already going to be evicting, so we just want to * continue to let page writes occur as quickly as possible. */ if (curproc == proc_pageout) { if (page_load > MAX(ptob(minfree), available_memory) / 4) return (ERESTART); /* Note: reserve is inflated, so we deflate */ page_load += reserve / 8; return (0); } else if (page_load > 0 && arc_reclaim_needed()) { /* memory is low, delay before restarting */ ARCSTAT_INCR(arcstat_memory_throttle_count, 1); return (EAGAIN); } page_load = 0; if (arc_size > arc_c_min) { uint64_t evictable_memory = arc_mru->arcs_lsize[ARC_BUFC_DATA] + arc_mru->arcs_lsize[ARC_BUFC_METADATA] + arc_mfu->arcs_lsize[ARC_BUFC_DATA] + arc_mfu->arcs_lsize[ARC_BUFC_METADATA]; available_memory += MIN(evictable_memory, arc_size - arc_c_min); } if (inflight_data > available_memory / 4) { ARCSTAT_INCR(arcstat_memory_throttle_count, 1); return (ERESTART); } #endif return (0); } void arc_tempreserve_clear(uint64_t reserve) { atomic_add_64(&arc_tempreserve, -reserve); ASSERT((int64_t)arc_tempreserve >= 0); } int arc_tempreserve_space(uint64_t reserve, uint64_t txg) { int error; #ifdef ZFS_DEBUG /* * Once in a while, fail for no reason. Everything should cope. */ if (spa_get_random(10000) == 0) { dprintf("forcing random failure\n"); return (ERESTART); } #endif if (reserve > arc_c/4 && !arc_no_grow) arc_c = MIN(arc_c_max, reserve * 4); if (reserve > arc_c) return (ENOMEM); /* * Writes will, almost always, require additional memory allocations * in order to compress/encrypt/etc the data. We therefor need to * make sure that there is sufficient available memory for this. */ if (error = arc_memory_throttle(reserve, txg)) return (error); /* * Throttle writes when the amount of dirty data in the cache * gets too large. We try to keep the cache less than half full * of dirty blocks so that our sync times don't grow too large. * Note: if two requests come in concurrently, we might let them * both succeed, when one of them should fail. Not a huge deal. */ if (reserve + arc_tempreserve + arc_anon->arcs_size > arc_c / 2 && arc_anon->arcs_size > arc_c / 4) { dprintf("failing, arc_tempreserve=%lluK anon_meta=%lluK " "anon_data=%lluK tempreserve=%lluK arc_c=%lluK\n", arc_tempreserve>>10, arc_anon->arcs_lsize[ARC_BUFC_METADATA]>>10, arc_anon->arcs_lsize[ARC_BUFC_DATA]>>10, reserve>>10, arc_c>>10); return (ERESTART); } atomic_add_64(&arc_tempreserve, reserve); return (0); } void arc_init(void) { mutex_init(&arc_reclaim_thr_lock, NULL, MUTEX_DEFAULT, NULL); cv_init(&arc_reclaim_thr_cv, NULL, CV_DEFAULT, NULL); /* Convert seconds to clock ticks */ arc_min_prefetch_lifespan = 1 * hz; /* Start out with 1/8 of all memory */ arc_c = physmem * PAGESIZE / 8; #ifdef _KERNEL /* * On architectures where the physical memory can be larger * than the addressable space (intel in 32-bit mode), we may * need to limit the cache to 1/8 of VM size. */ arc_c = MIN(arc_c, vmem_size(heap_arena, VMEM_ALLOC | VMEM_FREE) / 8); #endif /* set min cache to 1/32 of all memory, or 64MB, whichever is more */ arc_c_min = MAX(arc_c / 4, 64<<20); /* set max to 3/4 of all memory, or all but 1GB, whichever is more */ if (arc_c * 8 >= 1<<30) arc_c_max = (arc_c * 8) - (1<<30); else arc_c_max = arc_c_min; arc_c_max = MAX(arc_c * 6, arc_c_max); /* * Allow the tunables to override our calculations if they are * reasonable (ie. over 64MB) */ if (zfs_arc_max > 64<<20 && zfs_arc_max < physmem * PAGESIZE) arc_c_max = zfs_arc_max; if (zfs_arc_min > 64<<20 && zfs_arc_min <= arc_c_max) arc_c_min = zfs_arc_min; arc_c = arc_c_max; arc_p = (arc_c >> 1); /* limit meta-data to 1/4 of the arc capacity */ arc_meta_limit = arc_c_max / 4; /* Allow the tunable to override if it is reasonable */ if (zfs_arc_meta_limit > 0 && zfs_arc_meta_limit <= arc_c_max) arc_meta_limit = zfs_arc_meta_limit; if (arc_c_min < arc_meta_limit / 2 && zfs_arc_min == 0) arc_c_min = arc_meta_limit / 2; /* if kmem_flags are set, lets try to use less memory */ if (kmem_debugging()) arc_c = arc_c / 2; if (arc_c < arc_c_min) arc_c = arc_c_min; arc_anon = &ARC_anon; arc_mru = &ARC_mru; arc_mru_ghost = &ARC_mru_ghost; arc_mfu = &ARC_mfu; arc_mfu_ghost = &ARC_mfu_ghost; arc_l2c_only = &ARC_l2c_only; arc_size = 0; mutex_init(&arc_anon->arcs_mtx, NULL, MUTEX_DEFAULT, NULL); mutex_init(&arc_mru->arcs_mtx, NULL, MUTEX_DEFAULT, NULL); mutex_init(&arc_mru_ghost->arcs_mtx, NULL, MUTEX_DEFAULT, NULL); mutex_init(&arc_mfu->arcs_mtx, NULL, MUTEX_DEFAULT, NULL); mutex_init(&arc_mfu_ghost->arcs_mtx, NULL, MUTEX_DEFAULT, NULL); mutex_init(&arc_l2c_only->arcs_mtx, NULL, MUTEX_DEFAULT, NULL); list_create(&arc_mru->arcs_list[ARC_BUFC_METADATA], sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node)); list_create(&arc_mru->arcs_list[ARC_BUFC_DATA], sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node)); list_create(&arc_mru_ghost->arcs_list[ARC_BUFC_METADATA], sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node)); list_create(&arc_mru_ghost->arcs_list[ARC_BUFC_DATA], sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node)); list_create(&arc_mfu->arcs_list[ARC_BUFC_METADATA], sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node)); list_create(&arc_mfu->arcs_list[ARC_BUFC_DATA], sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node)); list_create(&arc_mfu_ghost->arcs_list[ARC_BUFC_METADATA], sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node)); list_create(&arc_mfu_ghost->arcs_list[ARC_BUFC_DATA], sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node)); list_create(&arc_l2c_only->arcs_list[ARC_BUFC_METADATA], sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node)); list_create(&arc_l2c_only->arcs_list[ARC_BUFC_DATA], sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_arc_node)); buf_init(); arc_thread_exit = 0; arc_eviction_list = NULL; mutex_init(&arc_eviction_mtx, NULL, MUTEX_DEFAULT, NULL); bzero(&arc_eviction_hdr, sizeof (arc_buf_hdr_t)); arc_ksp = kstat_create("zfs", 0, "arcstats", "misc", KSTAT_TYPE_NAMED, sizeof (arc_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL); if (arc_ksp != NULL) { arc_ksp->ks_data = &arc_stats; kstat_install(arc_ksp); } (void) thread_create(NULL, 0, arc_reclaim_thread, NULL, 0, &p0, TS_RUN, minclsyspri); arc_dead = FALSE; arc_warm = B_FALSE; if (zfs_write_limit_max == 0) zfs_write_limit_max = ptob(physmem) >> zfs_write_limit_shift; else zfs_write_limit_shift = 0; mutex_init(&zfs_write_limit_lock, NULL, MUTEX_DEFAULT, NULL); } void arc_fini(void) { mutex_enter(&arc_reclaim_thr_lock); arc_thread_exit = 1; while (arc_thread_exit != 0) cv_wait(&arc_reclaim_thr_cv, &arc_reclaim_thr_lock); mutex_exit(&arc_reclaim_thr_lock); arc_flush(NULL); arc_dead = TRUE; if (arc_ksp != NULL) { kstat_delete(arc_ksp); arc_ksp = NULL; } mutex_destroy(&arc_eviction_mtx); mutex_destroy(&arc_reclaim_thr_lock); cv_destroy(&arc_reclaim_thr_cv); list_destroy(&arc_mru->arcs_list[ARC_BUFC_METADATA]); list_destroy(&arc_mru_ghost->arcs_list[ARC_BUFC_METADATA]); list_destroy(&arc_mfu->arcs_list[ARC_BUFC_METADATA]); list_destroy(&arc_mfu_ghost->arcs_list[ARC_BUFC_METADATA]); list_destroy(&arc_mru->arcs_list[ARC_BUFC_DATA]); list_destroy(&arc_mru_ghost->arcs_list[ARC_BUFC_DATA]); list_destroy(&arc_mfu->arcs_list[ARC_BUFC_DATA]); list_destroy(&arc_mfu_ghost->arcs_list[ARC_BUFC_DATA]); mutex_destroy(&arc_anon->arcs_mtx); mutex_destroy(&arc_mru->arcs_mtx); mutex_destroy(&arc_mru_ghost->arcs_mtx); mutex_destroy(&arc_mfu->arcs_mtx); mutex_destroy(&arc_mfu_ghost->arcs_mtx); mutex_destroy(&arc_l2c_only->arcs_mtx); mutex_destroy(&zfs_write_limit_lock); buf_fini(); } /* * Level 2 ARC * * The level 2 ARC (L2ARC) is a cache layer in-between main memory and disk. * It uses dedicated storage devices to hold cached data, which are populated * using large infrequent writes. The main role of this cache is to boost * the performance of random read workloads. The intended L2ARC devices * include short-stroked disks, solid state disks, and other media with * substantially faster read latency than disk. * * +-----------------------+ * | ARC | * +-----------------------+ * | ^ ^ * | | | * l2arc_feed_thread() arc_read() * | | | * | l2arc read | * V | | * +---------------+ | * | L2ARC | | * +---------------+ | * | ^ | * l2arc_write() | | * | | | * V | | * +-------+ +-------+ * | vdev | | vdev | * | cache | | cache | * +-------+ +-------+ * +=========+ .-----. * : L2ARC : |-_____-| * : devices : | Disks | * +=========+ `-_____-' * * Read requests are satisfied from the following sources, in order: * * 1) ARC * 2) vdev cache of L2ARC devices * 3) L2ARC devices * 4) vdev cache of disks * 5) disks * * Some L2ARC device types exhibit extremely slow write performance. * To accommodate for this there are some significant differences between * the L2ARC and traditional cache design: * * 1. There is no eviction path from the ARC to the L2ARC. Evictions from * the ARC behave as usual, freeing buffers and placing headers on ghost * lists. The ARC does not send buffers to the L2ARC during eviction as * this would add inflated write latencies for all ARC memory pressure. * * 2. The L2ARC attempts to cache data from the ARC before it is evicted. * It does this by periodically scanning buffers from the eviction-end of * the MFU and MRU ARC lists, copying them to the L2ARC devices if they are * not already there. It scans until a headroom of buffers is satisfied, * which itself is a buffer for ARC eviction. The thread that does this is * l2arc_feed_thread(), illustrated below; example sizes are included to * provide a better sense of ratio than this diagram: * * head --> tail * +---------------------+----------+ * ARC_mfu |:::::#:::::::::::::::|o#o###o###|-->. # already on L2ARC * +---------------------+----------+ | o L2ARC eligible * ARC_mru |:#:::::::::::::::::::|#o#ooo####|-->| : ARC buffer * +---------------------+----------+ | * 15.9 Gbytes ^ 32 Mbytes | * headroom | * l2arc_feed_thread() * | * l2arc write hand <--[oooo]--' * | 8 Mbyte * | write max * V * +==============================+ * L2ARC dev |####|#|###|###| |####| ... | * +==============================+ * 32 Gbytes * * 3. If an ARC buffer is copied to the L2ARC but then hit instead of * evicted, then the L2ARC has cached a buffer much sooner than it probably * needed to, potentially wasting L2ARC device bandwidth and storage. It is * safe to say that this is an uncommon case, since buffers at the end of * the ARC lists have moved there due to inactivity. * * 4. If the ARC evicts faster than the L2ARC can maintain a headroom, * then the L2ARC simply misses copying some buffers. This serves as a * pressure valve to prevent heavy read workloads from both stalling the ARC * with waits and clogging the L2ARC with writes. This also helps prevent * the potential for the L2ARC to churn if it attempts to cache content too * quickly, such as during backups of the entire pool. * * 5. After system boot and before the ARC has filled main memory, there are * no evictions from the ARC and so the tails of the ARC_mfu and ARC_mru * lists can remain mostly static. Instead of searching from tail of these * lists as pictured, the l2arc_feed_thread() will search from the list heads * for eligible buffers, greatly increasing its chance of finding them. * * The L2ARC device write speed is also boosted during this time so that * the L2ARC warms up faster. Since there have been no ARC evictions yet, * there are no L2ARC reads, and no fear of degrading read performance * through increased writes. * * 6. Writes to the L2ARC devices are grouped and sent in-sequence, so that * the vdev queue can aggregate them into larger and fewer writes. Each * device is written to in a rotor fashion, sweeping writes through * available space then repeating. * * 7. The L2ARC does not store dirty content. It never needs to flush * write buffers back to disk based storage. * * 8. If an ARC buffer is written (and dirtied) which also exists in the * L2ARC, the now stale L2ARC buffer is immediately dropped. * * The performance of the L2ARC can be tweaked by a number of tunables, which * may be necessary for different workloads: * * l2arc_write_max max write bytes per interval * l2arc_write_boost extra write bytes during device warmup * l2arc_noprefetch skip caching prefetched buffers * l2arc_headroom number of max device writes to precache * l2arc_feed_secs seconds between L2ARC writing * * Tunables may be removed or added as future performance improvements are * integrated, and also may become zpool properties. */ static void l2arc_hdr_stat_add(void) { ARCSTAT_INCR(arcstat_l2_hdr_size, HDR_SIZE + L2HDR_SIZE); ARCSTAT_INCR(arcstat_hdr_size, -HDR_SIZE); } static void l2arc_hdr_stat_remove(void) { ARCSTAT_INCR(arcstat_l2_hdr_size, -(HDR_SIZE + L2HDR_SIZE)); ARCSTAT_INCR(arcstat_hdr_size, HDR_SIZE); } /* * Cycle through L2ARC devices. This is how L2ARC load balances. * If a device is returned, this also returns holding the spa config lock. */ static l2arc_dev_t * l2arc_dev_get_next(void) { l2arc_dev_t *first, *next = NULL; /* * Lock out the removal of spas (spa_namespace_lock), then removal * of cache devices (l2arc_dev_mtx). Once a device has been selected, * both locks will be dropped and a spa config lock held instead. */ mutex_enter(&spa_namespace_lock); mutex_enter(&l2arc_dev_mtx); /* if there are no vdevs, there is nothing to do */ if (l2arc_ndev == 0) goto out; first = NULL; next = l2arc_dev_last; do { /* loop around the list looking for a non-faulted vdev */ if (next == NULL) { next = list_head(l2arc_dev_list); } else { next = list_next(l2arc_dev_list, next); if (next == NULL) next = list_head(l2arc_dev_list); } /* if we have come back to the start, bail out */ if (first == NULL) first = next; else if (next == first) break; } while (vdev_is_dead(next->l2ad_vdev)); /* if we were unable to find any usable vdevs, return NULL */ if (vdev_is_dead(next->l2ad_vdev)) next = NULL; l2arc_dev_last = next; out: mutex_exit(&l2arc_dev_mtx); /* * Grab the config lock to prevent the 'next' device from being * removed while we are writing to it. */ if (next != NULL) spa_config_enter(next->l2ad_spa, SCL_L2ARC, next, RW_READER); mutex_exit(&spa_namespace_lock); return (next); } /* * Free buffers that were tagged for destruction. */ static void l2arc_do_free_on_write() { list_t *buflist; l2arc_data_free_t *df, *df_prev; mutex_enter(&l2arc_free_on_write_mtx); buflist = l2arc_free_on_write; for (df = list_tail(buflist); df; df = df_prev) { df_prev = list_prev(buflist, df); ASSERT(df->l2df_data != NULL); ASSERT(df->l2df_func != NULL); df->l2df_func(df->l2df_data, df->l2df_size); list_remove(buflist, df); kmem_free(df, sizeof (l2arc_data_free_t)); } mutex_exit(&l2arc_free_on_write_mtx); } /* * A write to a cache device has completed. Update all headers to allow * reads from these buffers to begin. */ static void l2arc_write_done(zio_t *zio) { l2arc_write_callback_t *cb; l2arc_dev_t *dev; list_t *buflist; arc_buf_hdr_t *head, *ab, *ab_prev; l2arc_buf_hdr_t *abl2; kmutex_t *hash_lock; cb = zio->io_private; ASSERT(cb != NULL); dev = cb->l2wcb_dev; ASSERT(dev != NULL); head = cb->l2wcb_head; ASSERT(head != NULL); buflist = dev->l2ad_buflist; ASSERT(buflist != NULL); DTRACE_PROBE2(l2arc__iodone, zio_t *, zio, l2arc_write_callback_t *, cb); if (zio->io_error != 0) ARCSTAT_BUMP(arcstat_l2_writes_error); mutex_enter(&l2arc_buflist_mtx); /* * All writes completed, or an error was hit. */ for (ab = list_prev(buflist, head); ab; ab = ab_prev) { ab_prev = list_prev(buflist, ab); hash_lock = HDR_LOCK(ab); if (!mutex_tryenter(hash_lock)) { /* * This buffer misses out. It may be in a stage * of eviction. Its ARC_L2_WRITING flag will be * left set, denying reads to this buffer. */ ARCSTAT_BUMP(arcstat_l2_writes_hdr_miss); continue; } if (zio->io_error != 0) { /* * Error - drop L2ARC entry. */ list_remove(buflist, ab); abl2 = ab->b_l2hdr; ab->b_l2hdr = NULL; kmem_free(abl2, sizeof (l2arc_buf_hdr_t)); ARCSTAT_INCR(arcstat_l2_size, -ab->b_size); } /* * Allow ARC to begin reads to this L2ARC entry. */ ab->b_flags &= ~ARC_L2_WRITING; mutex_exit(hash_lock); } atomic_inc_64(&l2arc_writes_done); list_remove(buflist, head); kmem_cache_free(hdr_cache, head); mutex_exit(&l2arc_buflist_mtx); l2arc_do_free_on_write(); kmem_free(cb, sizeof (l2arc_write_callback_t)); } /* * A read to a cache device completed. Validate buffer contents before * handing over to the regular ARC routines. */ static void l2arc_read_done(zio_t *zio) { l2arc_read_callback_t *cb; arc_buf_hdr_t *hdr; arc_buf_t *buf; kmutex_t *hash_lock; int equal; ASSERT(zio->io_vd != NULL); ASSERT(zio->io_flags & ZIO_FLAG_DONT_PROPAGATE); spa_config_exit(zio->io_spa, SCL_L2ARC, zio->io_vd); cb = zio->io_private; ASSERT(cb != NULL); buf = cb->l2rcb_buf; ASSERT(buf != NULL); hdr = buf->b_hdr; ASSERT(hdr != NULL); hash_lock = HDR_LOCK(hdr); mutex_enter(hash_lock); /* * Check this survived the L2ARC journey. */ equal = arc_cksum_equal(buf); if (equal && zio->io_error == 0 && !HDR_L2_EVICTED(hdr)) { mutex_exit(hash_lock); zio->io_private = buf; zio->io_bp_copy = cb->l2rcb_bp; /* XXX fix in L2ARC 2.0 */ zio->io_bp = &zio->io_bp_copy; /* XXX fix in L2ARC 2.0 */ arc_read_done(zio); } else { mutex_exit(hash_lock); /* * Buffer didn't survive caching. Increment stats and * reissue to the original storage device. */ if (zio->io_error != 0) { ARCSTAT_BUMP(arcstat_l2_io_error); } else { zio->io_error = EIO; } if (!equal) ARCSTAT_BUMP(arcstat_l2_cksum_bad); /* * If there's no waiter, issue an async i/o to the primary * storage now. If there *is* a waiter, the caller must * issue the i/o in a context where it's OK to block. */ if (zio->io_waiter == NULL) zio_nowait(zio_read(zio->io_parent, cb->l2rcb_spa, &cb->l2rcb_bp, buf->b_data, zio->io_size, arc_read_done, buf, zio->io_priority, cb->l2rcb_flags, &cb->l2rcb_zb)); } kmem_free(cb, sizeof (l2arc_read_callback_t)); } /* * This is the list priority from which the L2ARC will search for pages to * cache. This is used within loops (0..3) to cycle through lists in the * desired order. This order can have a significant effect on cache * performance. * * Currently the metadata lists are hit first, MFU then MRU, followed by * the data lists. This function returns a locked list, and also returns * the lock pointer. */ static list_t * l2arc_list_locked(int list_num, kmutex_t **lock) { list_t *list; ASSERT(list_num >= 0 && list_num <= 3); switch (list_num) { case 0: list = &arc_mfu->arcs_list[ARC_BUFC_METADATA]; *lock = &arc_mfu->arcs_mtx; break; case 1: list = &arc_mru->arcs_list[ARC_BUFC_METADATA]; *lock = &arc_mru->arcs_mtx; break; case 2: list = &arc_mfu->arcs_list[ARC_BUFC_DATA]; *lock = &arc_mfu->arcs_mtx; break; case 3: list = &arc_mru->arcs_list[ARC_BUFC_DATA]; *lock = &arc_mru->arcs_mtx; break; } ASSERT(!(MUTEX_HELD(*lock))); mutex_enter(*lock); return (list); } /* * Evict buffers from the device write hand to the distance specified in * bytes. This distance may span populated buffers, it may span nothing. * This is clearing a region on the L2ARC device ready for writing. * If the 'all' boolean is set, every buffer is evicted. */ static void l2arc_evict(l2arc_dev_t *dev, uint64_t distance, boolean_t all) { list_t *buflist; l2arc_buf_hdr_t *abl2; arc_buf_hdr_t *ab, *ab_prev; kmutex_t *hash_lock; uint64_t taddr; buflist = dev->l2ad_buflist; if (buflist == NULL) return; if (!all && dev->l2ad_first) { /* * This is the first sweep through the device. There is * nothing to evict. */ return; } if (dev->l2ad_hand >= (dev->l2ad_end - (2 * distance))) { /* * When nearing the end of the device, evict to the end * before the device write hand jumps to the start. */ taddr = dev->l2ad_end; } else { taddr = dev->l2ad_hand + distance; } DTRACE_PROBE4(l2arc__evict, l2arc_dev_t *, dev, list_t *, buflist, uint64_t, taddr, boolean_t, all); top: mutex_enter(&l2arc_buflist_mtx); for (ab = list_tail(buflist); ab; ab = ab_prev) { ab_prev = list_prev(buflist, ab); hash_lock = HDR_LOCK(ab); if (!mutex_tryenter(hash_lock)) { /* * Missed the hash lock. Retry. */ ARCSTAT_BUMP(arcstat_l2_evict_lock_retry); mutex_exit(&l2arc_buflist_mtx); mutex_enter(hash_lock); mutex_exit(hash_lock); goto top; } if (HDR_L2_WRITE_HEAD(ab)) { /* * We hit a write head node. Leave it for * l2arc_write_done(). */ list_remove(buflist, ab); mutex_exit(hash_lock); continue; } if (!all && ab->b_l2hdr != NULL && (ab->b_l2hdr->b_daddr > taddr || ab->b_l2hdr->b_daddr < dev->l2ad_hand)) { /* * We've evicted to the target address, * or the end of the device. */ mutex_exit(hash_lock); break; } if (HDR_FREE_IN_PROGRESS(ab)) { /* * Already on the path to destruction. */ mutex_exit(hash_lock); continue; } if (ab->b_state == arc_l2c_only) { ASSERT(!HDR_L2_READING(ab)); /* * This doesn't exist in the ARC. Destroy. * arc_hdr_destroy() will call list_remove() * and decrement arcstat_l2_size. */ arc_change_state(arc_anon, ab, hash_lock); arc_hdr_destroy(ab); } else { /* * Invalidate issued or about to be issued * reads, since we may be about to write * over this location. */ if (HDR_L2_READING(ab)) { ARCSTAT_BUMP(arcstat_l2_evict_reading); ab->b_flags |= ARC_L2_EVICTED; } /* * Tell ARC this no longer exists in L2ARC. */ if (ab->b_l2hdr != NULL) { abl2 = ab->b_l2hdr; ab->b_l2hdr = NULL; kmem_free(abl2, sizeof (l2arc_buf_hdr_t)); ARCSTAT_INCR(arcstat_l2_size, -ab->b_size); } list_remove(buflist, ab); /* * This may have been leftover after a * failed write. */ ab->b_flags &= ~ARC_L2_WRITING; } mutex_exit(hash_lock); } mutex_exit(&l2arc_buflist_mtx); spa_l2cache_space_update(dev->l2ad_vdev, 0, -(taddr - dev->l2ad_evict)); dev->l2ad_evict = taddr; } /* * Find and write ARC buffers to the L2ARC device. * * An ARC_L2_WRITING flag is set so that the L2ARC buffers are not valid * for reading until they have completed writing. */ static void l2arc_write_buffers(spa_t *spa, l2arc_dev_t *dev, uint64_t target_sz) { arc_buf_hdr_t *ab, *ab_prev, *head; l2arc_buf_hdr_t *hdrl2; list_t *list; uint64_t passed_sz, write_sz, buf_sz, headroom; void *buf_data; kmutex_t *hash_lock, *list_lock; boolean_t have_lock, full; l2arc_write_callback_t *cb; zio_t *pio, *wzio; ASSERT(dev->l2ad_vdev != NULL); pio = NULL; write_sz = 0; full = B_FALSE; head = kmem_cache_alloc(hdr_cache, KM_PUSHPAGE); head->b_flags |= ARC_L2_WRITE_HEAD; /* * Copy buffers for L2ARC writing. */ mutex_enter(&l2arc_buflist_mtx); for (int try = 0; try <= 3; try++) { list = l2arc_list_locked(try, &list_lock); passed_sz = 0; /* * L2ARC fast warmup. * * Until the ARC is warm and starts to evict, read from the * head of the ARC lists rather than the tail. */ headroom = target_sz * l2arc_headroom; if (arc_warm == B_FALSE) ab = list_head(list); else ab = list_tail(list); for (; ab; ab = ab_prev) { if (arc_warm == B_FALSE) ab_prev = list_next(list, ab); else ab_prev = list_prev(list, ab); hash_lock = HDR_LOCK(ab); have_lock = MUTEX_HELD(hash_lock); if (!have_lock && !mutex_tryenter(hash_lock)) { /* * Skip this buffer rather than waiting. */ continue; } passed_sz += ab->b_size; if (passed_sz > headroom) { /* * Searched too far. */ mutex_exit(hash_lock); break; } if (ab->b_spa != spa) { mutex_exit(hash_lock); continue; } if (ab->b_l2hdr != NULL) { /* * Already in L2ARC. */ mutex_exit(hash_lock); continue; } if (HDR_IO_IN_PROGRESS(ab) || !HDR_L2CACHE(ab)) { mutex_exit(hash_lock); continue; } if ((write_sz + ab->b_size) > target_sz) { full = B_TRUE; mutex_exit(hash_lock); break; } if (ab->b_buf == NULL) { DTRACE_PROBE1(l2arc__buf__null, void *, ab); mutex_exit(hash_lock); continue; } if (pio == NULL) { /* * Insert a dummy header on the buflist so * l2arc_write_done() can find where the * write buffers begin without searching. */ list_insert_head(dev->l2ad_buflist, head); cb = kmem_alloc( sizeof (l2arc_write_callback_t), KM_SLEEP); cb->l2wcb_dev = dev; cb->l2wcb_head = head; pio = zio_root(spa, l2arc_write_done, cb, ZIO_FLAG_CANFAIL); } /* * Create and add a new L2ARC header. */ hdrl2 = kmem_zalloc(sizeof (l2arc_buf_hdr_t), KM_SLEEP); hdrl2->b_dev = dev; hdrl2->b_daddr = dev->l2ad_hand; ab->b_flags |= ARC_L2_WRITING; ab->b_l2hdr = hdrl2; list_insert_head(dev->l2ad_buflist, ab); buf_data = ab->b_buf->b_data; buf_sz = ab->b_size; /* * Compute and store the buffer cksum before * writing. On debug the cksum is verified first. */ arc_cksum_verify(ab->b_buf); arc_cksum_compute(ab->b_buf, B_TRUE); mutex_exit(hash_lock); wzio = zio_write_phys(pio, dev->l2ad_vdev, dev->l2ad_hand, buf_sz, buf_data, ZIO_CHECKSUM_OFF, NULL, NULL, ZIO_PRIORITY_ASYNC_WRITE, ZIO_FLAG_CANFAIL, B_FALSE); DTRACE_PROBE2(l2arc__write, vdev_t *, dev->l2ad_vdev, zio_t *, wzio); (void) zio_nowait(wzio); /* * Keep the clock hand suitably device-aligned. */ buf_sz = vdev_psize_to_asize(dev->l2ad_vdev, buf_sz); write_sz += buf_sz; dev->l2ad_hand += buf_sz; } mutex_exit(list_lock); if (full == B_TRUE) break; } mutex_exit(&l2arc_buflist_mtx); if (pio == NULL) { ASSERT3U(write_sz, ==, 0); kmem_cache_free(hdr_cache, head); return; } ASSERT3U(write_sz, <=, target_sz); ARCSTAT_BUMP(arcstat_l2_writes_sent); ARCSTAT_INCR(arcstat_l2_size, write_sz); spa_l2cache_space_update(dev->l2ad_vdev, 0, write_sz); /* * Bump device hand to the device start if it is approaching the end. * l2arc_evict() will already have evicted ahead for this case. */ if (dev->l2ad_hand >= (dev->l2ad_end - target_sz)) { spa_l2cache_space_update(dev->l2ad_vdev, 0, dev->l2ad_end - dev->l2ad_hand); dev->l2ad_hand = dev->l2ad_start; dev->l2ad_evict = dev->l2ad_start; dev->l2ad_first = B_FALSE; } (void) zio_wait(pio); } /* * This thread feeds the L2ARC at regular intervals. This is the beating * heart of the L2ARC. */ static void l2arc_feed_thread(void) { callb_cpr_t cpr; l2arc_dev_t *dev; spa_t *spa; uint64_t size; CALLB_CPR_INIT(&cpr, &l2arc_feed_thr_lock, callb_generic_cpr, FTAG); mutex_enter(&l2arc_feed_thr_lock); while (l2arc_thread_exit == 0) { /* * Pause for l2arc_feed_secs seconds between writes. */ CALLB_CPR_SAFE_BEGIN(&cpr); (void) cv_timedwait(&l2arc_feed_thr_cv, &l2arc_feed_thr_lock, lbolt + (hz * l2arc_feed_secs)); CALLB_CPR_SAFE_END(&cpr, &l2arc_feed_thr_lock); /* * Quick check for L2ARC devices. */ mutex_enter(&l2arc_dev_mtx); if (l2arc_ndev == 0) { mutex_exit(&l2arc_dev_mtx); continue; } mutex_exit(&l2arc_dev_mtx); /* * This selects the next l2arc device to write to, and in * doing so the next spa to feed from: dev->l2ad_spa. This * will return NULL if there are now no l2arc devices or if * they are all faulted. * * If a device is returned, its spa's config lock is also * held to prevent device removal. l2arc_dev_get_next() * will grab and release l2arc_dev_mtx. */ if ((dev = l2arc_dev_get_next()) == NULL) continue; spa = dev->l2ad_spa; ASSERT(spa != NULL); /* * Avoid contributing to memory pressure. */ if (arc_reclaim_needed()) { ARCSTAT_BUMP(arcstat_l2_abort_lowmem); spa_config_exit(spa, SCL_L2ARC, dev); continue; } ARCSTAT_BUMP(arcstat_l2_feeds); size = dev->l2ad_write; if (arc_warm == B_FALSE) size += dev->l2ad_boost; /* * Evict L2ARC buffers that will be overwritten. */ l2arc_evict(dev, size, B_FALSE); /* * Write ARC buffers. */ l2arc_write_buffers(spa, dev, size); spa_config_exit(spa, SCL_L2ARC, dev); } l2arc_thread_exit = 0; cv_broadcast(&l2arc_feed_thr_cv); CALLB_CPR_EXIT(&cpr); /* drops l2arc_feed_thr_lock */ thread_exit(); } boolean_t l2arc_vdev_present(vdev_t *vd) { l2arc_dev_t *dev; mutex_enter(&l2arc_dev_mtx); for (dev = list_head(l2arc_dev_list); dev != NULL; dev = list_next(l2arc_dev_list, dev)) { if (dev->l2ad_vdev == vd) break; } mutex_exit(&l2arc_dev_mtx); return (dev != NULL); } /* * Add a vdev for use by the L2ARC. By this point the spa has already * validated the vdev and opened it. */ void l2arc_add_vdev(spa_t *spa, vdev_t *vd, uint64_t start, uint64_t end) { l2arc_dev_t *adddev; ASSERT(!l2arc_vdev_present(vd)); /* * Create a new l2arc device entry. */ adddev = kmem_zalloc(sizeof (l2arc_dev_t), KM_SLEEP); adddev->l2ad_spa = spa; adddev->l2ad_vdev = vd; adddev->l2ad_write = l2arc_write_max; adddev->l2ad_boost = l2arc_write_boost; adddev->l2ad_start = start; adddev->l2ad_end = end; adddev->l2ad_hand = adddev->l2ad_start; adddev->l2ad_evict = adddev->l2ad_start; adddev->l2ad_first = B_TRUE; ASSERT3U(adddev->l2ad_write, >, 0); /* * This is a list of all ARC buffers that are still valid on the * device. */ adddev->l2ad_buflist = kmem_zalloc(sizeof (list_t), KM_SLEEP); list_create(adddev->l2ad_buflist, sizeof (arc_buf_hdr_t), offsetof(arc_buf_hdr_t, b_l2node)); spa_l2cache_space_update(vd, adddev->l2ad_end - adddev->l2ad_hand, 0); /* * Add device to global list */ mutex_enter(&l2arc_dev_mtx); list_insert_head(l2arc_dev_list, adddev); atomic_inc_64(&l2arc_ndev); mutex_exit(&l2arc_dev_mtx); } /* * Remove a vdev from the L2ARC. */ void l2arc_remove_vdev(vdev_t *vd) { l2arc_dev_t *dev, *nextdev, *remdev = NULL; /* * Find the device by vdev */ mutex_enter(&l2arc_dev_mtx); for (dev = list_head(l2arc_dev_list); dev; dev = nextdev) { nextdev = list_next(l2arc_dev_list, dev); if (vd == dev->l2ad_vdev) { remdev = dev; break; } } ASSERT(remdev != NULL); /* * Remove device from global list */ list_remove(l2arc_dev_list, remdev); l2arc_dev_last = NULL; /* may have been invalidated */ atomic_dec_64(&l2arc_ndev); mutex_exit(&l2arc_dev_mtx); /* * Clear all buflists and ARC references. L2ARC device flush. */ l2arc_evict(remdev, 0, B_TRUE); list_destroy(remdev->l2ad_buflist); kmem_free(remdev->l2ad_buflist, sizeof (list_t)); kmem_free(remdev, sizeof (l2arc_dev_t)); } void l2arc_init(void) { l2arc_thread_exit = 0; l2arc_ndev = 0; l2arc_writes_sent = 0; l2arc_writes_done = 0; mutex_init(&l2arc_feed_thr_lock, NULL, MUTEX_DEFAULT, NULL); cv_init(&l2arc_feed_thr_cv, NULL, CV_DEFAULT, NULL); mutex_init(&l2arc_dev_mtx, NULL, MUTEX_DEFAULT, NULL); mutex_init(&l2arc_buflist_mtx, NULL, MUTEX_DEFAULT, NULL); mutex_init(&l2arc_free_on_write_mtx, NULL, MUTEX_DEFAULT, NULL); l2arc_dev_list = &L2ARC_dev_list; l2arc_free_on_write = &L2ARC_free_on_write; list_create(l2arc_dev_list, sizeof (l2arc_dev_t), offsetof(l2arc_dev_t, l2ad_node)); list_create(l2arc_free_on_write, sizeof (l2arc_data_free_t), offsetof(l2arc_data_free_t, l2df_list_node)); } void l2arc_fini(void) { /* * This is called from dmu_fini(), which is called from spa_fini(); * Because of this, we can assume that all l2arc devices have * already been removed when the pools themselves were removed. */ l2arc_do_free_on_write(); mutex_destroy(&l2arc_feed_thr_lock); cv_destroy(&l2arc_feed_thr_cv); mutex_destroy(&l2arc_dev_mtx); mutex_destroy(&l2arc_buflist_mtx); mutex_destroy(&l2arc_free_on_write_mtx); list_destroy(l2arc_dev_list); list_destroy(l2arc_free_on_write); } void l2arc_start(void) { if (!(spa_mode_global & FWRITE)) return; (void) thread_create(NULL, 0, l2arc_feed_thread, NULL, 0, &p0, TS_RUN, minclsyspri); } void l2arc_stop(void) { if (!(spa_mode_global & FWRITE)) return; mutex_enter(&l2arc_feed_thr_lock); cv_signal(&l2arc_feed_thr_cv); /* kick thread out of startup */ l2arc_thread_exit = 1; while (l2arc_thread_exit != 0) cv_wait(&l2arc_feed_thr_cv, &l2arc_feed_thr_lock); mutex_exit(&l2arc_feed_thr_lock); }