/* * 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 https://opensource.org/licenses/CDDL-1.0. * 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 (c) 2014 by Chunwei Chen. All rights reserved. * Copyright (c) 2019 by Delphix. All rights reserved. * Copyright (c) 2023, 2024, Klara Inc. */ /* * See abd.c for a general overview of the arc buffered data (ABD). * * Linear buffers act exactly like normal buffers and are always mapped into the * kernel's virtual memory space, while scattered ABD data chunks are allocated * as physical pages and then mapped in only while they are actually being * accessed through one of the abd_* library functions. Using scattered ABDs * provides several benefits: * * (1) They avoid use of kmem_*, preventing performance problems where running * kmem_reap on very large memory systems never finishes and causes * constant TLB shootdowns. * * (2) Fragmentation is less of an issue since when we are at the limit of * allocatable space, we won't have to search around for a long free * hole in the VA space for large ARC allocations. Each chunk is mapped in * individually, so even if we are using HIGHMEM (see next point) we * wouldn't need to worry about finding a contiguous address range. * * (3) If we are not using HIGHMEM, then all physical memory is always * mapped into the kernel's address space, so we also avoid the map / * unmap costs on each ABD access. * * If we are not using HIGHMEM, scattered buffers which have only one chunk * can be treated as linear buffers, because they are contiguous in the * kernel's virtual address space. See abd_alloc_chunks() for details. */ #include #include #include #include #include #include #include #include #include #include #if defined(MAX_ORDER) #define ABD_MAX_ORDER (MAX_ORDER) #elif defined(MAX_PAGE_ORDER) #define ABD_MAX_ORDER (MAX_PAGE_ORDER) #endif typedef struct abd_stats { kstat_named_t abdstat_struct_size; kstat_named_t abdstat_linear_cnt; kstat_named_t abdstat_linear_data_size; kstat_named_t abdstat_scatter_cnt; kstat_named_t abdstat_scatter_data_size; kstat_named_t abdstat_scatter_chunk_waste; kstat_named_t abdstat_scatter_orders[ABD_MAX_ORDER]; kstat_named_t abdstat_scatter_page_multi_chunk; kstat_named_t abdstat_scatter_page_multi_zone; kstat_named_t abdstat_scatter_page_alloc_retry; kstat_named_t abdstat_scatter_sg_table_retry; } abd_stats_t; static abd_stats_t abd_stats = { /* Amount of memory occupied by all of the abd_t struct allocations */ { "struct_size", KSTAT_DATA_UINT64 }, /* * The number of linear ABDs which are currently allocated, excluding * ABDs which don't own their data (for instance the ones which were * allocated through abd_get_offset() and abd_get_from_buf()). If an * ABD takes ownership of its buf then it will become tracked. */ { "linear_cnt", KSTAT_DATA_UINT64 }, /* Amount of data stored in all linear ABDs tracked by linear_cnt */ { "linear_data_size", KSTAT_DATA_UINT64 }, /* * The number of scatter ABDs which are currently allocated, excluding * ABDs which don't own their data (for instance the ones which were * allocated through abd_get_offset()). */ { "scatter_cnt", KSTAT_DATA_UINT64 }, /* Amount of data stored in all scatter ABDs tracked by scatter_cnt */ { "scatter_data_size", KSTAT_DATA_UINT64 }, /* * The amount of space wasted at the end of the last chunk across all * scatter ABDs tracked by scatter_cnt. */ { "scatter_chunk_waste", KSTAT_DATA_UINT64 }, /* * The number of compound allocations of a given order. These * allocations are spread over all currently allocated ABDs, and * act as a measure of memory fragmentation. */ { { "scatter_order_N", KSTAT_DATA_UINT64 } }, /* * The number of scatter ABDs which contain multiple chunks. * ABDs are preferentially allocated from the minimum number of * contiguous multi-page chunks, a single chunk is optimal. */ { "scatter_page_multi_chunk", KSTAT_DATA_UINT64 }, /* * The number of scatter ABDs which are split across memory zones. * ABDs are preferentially allocated using pages from a single zone. */ { "scatter_page_multi_zone", KSTAT_DATA_UINT64 }, /* * The total number of retries encountered when attempting to * allocate the pages to populate the scatter ABD. */ { "scatter_page_alloc_retry", KSTAT_DATA_UINT64 }, /* * The total number of retries encountered when attempting to * allocate the sg table for an ABD. */ { "scatter_sg_table_retry", KSTAT_DATA_UINT64 }, }; static struct { wmsum_t abdstat_struct_size; wmsum_t abdstat_linear_cnt; wmsum_t abdstat_linear_data_size; wmsum_t abdstat_scatter_cnt; wmsum_t abdstat_scatter_data_size; wmsum_t abdstat_scatter_chunk_waste; wmsum_t abdstat_scatter_orders[ABD_MAX_ORDER]; wmsum_t abdstat_scatter_page_multi_chunk; wmsum_t abdstat_scatter_page_multi_zone; wmsum_t abdstat_scatter_page_alloc_retry; wmsum_t abdstat_scatter_sg_table_retry; } abd_sums; #define abd_for_each_sg(abd, sg, n, i) \ for_each_sg(ABD_SCATTER(abd).abd_sgl, sg, n, i) /* * zfs_abd_scatter_min_size is the minimum allocation size to use scatter * ABD's. Smaller allocations will use linear ABD's which uses * zio_[data_]buf_alloc(). * * Scatter ABD's use at least one page each, so sub-page allocations waste * some space when allocated as scatter (e.g. 2KB scatter allocation wastes * half of each page). Using linear ABD's for small allocations means that * they will be put on slabs which contain many allocations. This can * improve memory efficiency, but it also makes it much harder for ARC * evictions to actually free pages, because all the buffers on one slab need * to be freed in order for the slab (and underlying pages) to be freed. * Typically, 512B and 1KB kmem caches have 16 buffers per slab, so it's * possible for them to actually waste more memory than scatter (one page per * buf = wasting 3/4 or 7/8th; one buf per slab = wasting 15/16th). * * Spill blocks are typically 512B and are heavily used on systems running * selinux with the default dnode size and the `xattr=sa` property set. * * By default we use linear allocations for 512B and 1KB, and scatter * allocations for larger (1.5KB and up). */ static int zfs_abd_scatter_min_size = 512 * 3; /* * We use a scattered SPA_MAXBLOCKSIZE sized ABD whose pages are * just a single zero'd page. This allows us to conserve memory by * only using a single zero page for the scatterlist. */ abd_t *abd_zero_scatter = NULL; struct page; /* * abd_zero_page is assigned to each of the pages of abd_zero_scatter. It will * point to ZERO_PAGE if it is available or it will be an allocated zero'd * PAGESIZE buffer. */ static struct page *abd_zero_page = NULL; static kmem_cache_t *abd_cache = NULL; static kstat_t *abd_ksp; static uint_t abd_chunkcnt_for_bytes(size_t size) { return (P2ROUNDUP(size, PAGESIZE) / PAGESIZE); } abd_t * abd_alloc_struct_impl(size_t size) { /* * In Linux we do not use the size passed in during ABD * allocation, so we just ignore it. */ (void) size; abd_t *abd = kmem_cache_alloc(abd_cache, KM_PUSHPAGE); ASSERT3P(abd, !=, NULL); ABDSTAT_INCR(abdstat_struct_size, sizeof (abd_t)); return (abd); } void abd_free_struct_impl(abd_t *abd) { kmem_cache_free(abd_cache, abd); ABDSTAT_INCR(abdstat_struct_size, -(int)sizeof (abd_t)); } static unsigned zfs_abd_scatter_max_order = ABD_MAX_ORDER - 1; /* * Mark zfs data pages so they can be excluded from kernel crash dumps */ #ifdef _LP64 #define ABD_FILE_CACHE_PAGE 0x2F5ABDF11ECAC4E static inline void abd_mark_zfs_page(struct page *page) { get_page(page); SetPagePrivate(page); set_page_private(page, ABD_FILE_CACHE_PAGE); } static inline void abd_unmark_zfs_page(struct page *page) { set_page_private(page, 0UL); ClearPagePrivate(page); put_page(page); } #else #define abd_mark_zfs_page(page) #define abd_unmark_zfs_page(page) #endif /* _LP64 */ #ifndef CONFIG_HIGHMEM #ifndef __GFP_RECLAIM #define __GFP_RECLAIM __GFP_WAIT #endif /* * The goal is to minimize fragmentation by preferentially populating ABDs * with higher order compound pages from a single zone. Allocation size is * progressively decreased until it can be satisfied without performing * reclaim or compaction. When necessary this function will degenerate to * allocating individual pages and allowing reclaim to satisfy allocations. */ void abd_alloc_chunks(abd_t *abd, size_t size) { struct list_head pages; struct sg_table table; struct scatterlist *sg; struct page *page, *tmp_page = NULL; gfp_t gfp = __GFP_RECLAIMABLE | __GFP_NOWARN | GFP_NOIO; gfp_t gfp_comp = (gfp | __GFP_NORETRY | __GFP_COMP) & ~__GFP_RECLAIM; unsigned int max_order = MIN(zfs_abd_scatter_max_order, ABD_MAX_ORDER - 1); unsigned int nr_pages = abd_chunkcnt_for_bytes(size); unsigned int chunks = 0, zones = 0; size_t remaining_size; int nid = NUMA_NO_NODE; unsigned int alloc_pages = 0; INIT_LIST_HEAD(&pages); ASSERT3U(alloc_pages, <, nr_pages); while (alloc_pages < nr_pages) { unsigned int chunk_pages; unsigned int order; order = MIN(highbit64(nr_pages - alloc_pages) - 1, max_order); chunk_pages = (1U << order); page = alloc_pages_node(nid, order ? gfp_comp : gfp, order); if (page == NULL) { if (order == 0) { ABDSTAT_BUMP(abdstat_scatter_page_alloc_retry); schedule_timeout_interruptible(1); } else { max_order = MAX(0, order - 1); } continue; } list_add_tail(&page->lru, &pages); if ((nid != NUMA_NO_NODE) && (page_to_nid(page) != nid)) zones++; nid = page_to_nid(page); ABDSTAT_BUMP(abdstat_scatter_orders[order]); chunks++; alloc_pages += chunk_pages; } ASSERT3S(alloc_pages, ==, nr_pages); while (sg_alloc_table(&table, chunks, gfp)) { ABDSTAT_BUMP(abdstat_scatter_sg_table_retry); schedule_timeout_interruptible(1); } sg = table.sgl; remaining_size = size; list_for_each_entry_safe(page, tmp_page, &pages, lru) { size_t sg_size = MIN(PAGESIZE << compound_order(page), remaining_size); sg_set_page(sg, page, sg_size, 0); abd_mark_zfs_page(page); remaining_size -= sg_size; sg = sg_next(sg); list_del(&page->lru); } /* * These conditions ensure that a possible transformation to a linear * ABD would be valid. */ ASSERT(!PageHighMem(sg_page(table.sgl))); ASSERT0(ABD_SCATTER(abd).abd_offset); if (table.nents == 1) { /* * Since there is only one entry, this ABD can be represented * as a linear buffer. All single-page (4K) ABD's can be * represented this way. Some multi-page ABD's can also be * represented this way, if we were able to allocate a single * "chunk" (higher-order "page" which represents a power-of-2 * series of physically-contiguous pages). This is often the * case for 2-page (8K) ABD's. * * Representing a single-entry scatter ABD as a linear ABD * has the performance advantage of avoiding the copy (and * allocation) in abd_borrow_buf_copy / abd_return_buf_copy. * A performance increase of around 5% has been observed for * ARC-cached reads (of small blocks which can take advantage * of this). * * Note that this optimization is only possible because the * pages are always mapped into the kernel's address space. * This is not the case for highmem pages, so the * optimization can not be made there. */ abd->abd_flags |= ABD_FLAG_LINEAR; abd->abd_flags |= ABD_FLAG_LINEAR_PAGE; abd->abd_u.abd_linear.abd_sgl = table.sgl; ABD_LINEAR_BUF(abd) = page_address(sg_page(table.sgl)); } else if (table.nents > 1) { ABDSTAT_BUMP(abdstat_scatter_page_multi_chunk); abd->abd_flags |= ABD_FLAG_MULTI_CHUNK; if (zones) { ABDSTAT_BUMP(abdstat_scatter_page_multi_zone); abd->abd_flags |= ABD_FLAG_MULTI_ZONE; } ABD_SCATTER(abd).abd_sgl = table.sgl; ABD_SCATTER(abd).abd_nents = table.nents; } } #else /* * Allocate N individual pages to construct a scatter ABD. This function * makes no attempt to request contiguous pages and requires the minimal * number of kernel interfaces. It's designed for maximum compatibility. */ void abd_alloc_chunks(abd_t *abd, size_t size) { struct scatterlist *sg = NULL; struct sg_table table; struct page *page; gfp_t gfp = __GFP_RECLAIMABLE | __GFP_NOWARN | GFP_NOIO; int nr_pages = abd_chunkcnt_for_bytes(size); int i = 0; while (sg_alloc_table(&table, nr_pages, gfp)) { ABDSTAT_BUMP(abdstat_scatter_sg_table_retry); schedule_timeout_interruptible(1); } ASSERT3U(table.nents, ==, nr_pages); ABD_SCATTER(abd).abd_sgl = table.sgl; ABD_SCATTER(abd).abd_nents = nr_pages; abd_for_each_sg(abd, sg, nr_pages, i) { while ((page = __page_cache_alloc(gfp)) == NULL) { ABDSTAT_BUMP(abdstat_scatter_page_alloc_retry); schedule_timeout_interruptible(1); } ABDSTAT_BUMP(abdstat_scatter_orders[0]); sg_set_page(sg, page, PAGESIZE, 0); abd_mark_zfs_page(page); } if (nr_pages > 1) { ABDSTAT_BUMP(abdstat_scatter_page_multi_chunk); abd->abd_flags |= ABD_FLAG_MULTI_CHUNK; } } #endif /* !CONFIG_HIGHMEM */ /* * This must be called if any of the sg_table allocation functions * are called. */ static void abd_free_sg_table(abd_t *abd) { struct sg_table table; table.sgl = ABD_SCATTER(abd).abd_sgl; table.nents = table.orig_nents = ABD_SCATTER(abd).abd_nents; sg_free_table(&table); } void abd_free_chunks(abd_t *abd) { struct scatterlist *sg = NULL; struct page *page; int nr_pages = ABD_SCATTER(abd).abd_nents; int order, i = 0; if (abd->abd_flags & ABD_FLAG_MULTI_ZONE) ABDSTAT_BUMPDOWN(abdstat_scatter_page_multi_zone); if (abd->abd_flags & ABD_FLAG_MULTI_CHUNK) ABDSTAT_BUMPDOWN(abdstat_scatter_page_multi_chunk); /* * Scatter ABDs may be constructed by abd_alloc_from_pages() from * an array of pages. In which case they should not be freed. */ if (!abd_is_from_pages(abd)) { abd_for_each_sg(abd, sg, nr_pages, i) { page = sg_page(sg); abd_unmark_zfs_page(page); order = compound_order(page); __free_pages(page, order); ASSERT3U(sg->length, <=, PAGE_SIZE << order); ABDSTAT_BUMPDOWN(abdstat_scatter_orders[order]); } } abd_free_sg_table(abd); } /* * Allocate scatter ABD of size SPA_MAXBLOCKSIZE, where each page in * the scatterlist will be set to the zero'd out buffer abd_zero_page. */ static void abd_alloc_zero_scatter(void) { struct scatterlist *sg = NULL; struct sg_table table; gfp_t gfp = __GFP_NOWARN | GFP_NOIO; int nr_pages = abd_chunkcnt_for_bytes(SPA_MAXBLOCKSIZE); int i = 0; #if defined(HAVE_ZERO_PAGE_GPL_ONLY) gfp_t gfp_zero_page = gfp | __GFP_ZERO; while ((abd_zero_page = __page_cache_alloc(gfp_zero_page)) == NULL) { ABDSTAT_BUMP(abdstat_scatter_page_alloc_retry); schedule_timeout_interruptible(1); } abd_mark_zfs_page(abd_zero_page); #else abd_zero_page = ZERO_PAGE(0); #endif /* HAVE_ZERO_PAGE_GPL_ONLY */ while (sg_alloc_table(&table, nr_pages, gfp)) { ABDSTAT_BUMP(abdstat_scatter_sg_table_retry); schedule_timeout_interruptible(1); } ASSERT3U(table.nents, ==, nr_pages); abd_zero_scatter = abd_alloc_struct(SPA_MAXBLOCKSIZE); abd_zero_scatter->abd_flags |= ABD_FLAG_OWNER; ABD_SCATTER(abd_zero_scatter).abd_offset = 0; ABD_SCATTER(abd_zero_scatter).abd_sgl = table.sgl; ABD_SCATTER(abd_zero_scatter).abd_nents = nr_pages; abd_zero_scatter->abd_size = SPA_MAXBLOCKSIZE; abd_zero_scatter->abd_flags |= ABD_FLAG_MULTI_CHUNK; abd_for_each_sg(abd_zero_scatter, sg, nr_pages, i) { sg_set_page(sg, abd_zero_page, PAGESIZE, 0); } ABDSTAT_BUMP(abdstat_scatter_cnt); ABDSTAT_INCR(abdstat_scatter_data_size, PAGESIZE); ABDSTAT_BUMP(abdstat_scatter_page_multi_chunk); } boolean_t abd_size_alloc_linear(size_t size) { return (!zfs_abd_scatter_enabled || size < zfs_abd_scatter_min_size); } void abd_update_scatter_stats(abd_t *abd, abd_stats_op_t op) { ASSERT(op == ABDSTAT_INCR || op == ABDSTAT_DECR); int waste = P2ROUNDUP(abd->abd_size, PAGESIZE) - abd->abd_size; if (op == ABDSTAT_INCR) { ABDSTAT_BUMP(abdstat_scatter_cnt); ABDSTAT_INCR(abdstat_scatter_data_size, abd->abd_size); ABDSTAT_INCR(abdstat_scatter_chunk_waste, waste); arc_space_consume(waste, ARC_SPACE_ABD_CHUNK_WASTE); } else { ABDSTAT_BUMPDOWN(abdstat_scatter_cnt); ABDSTAT_INCR(abdstat_scatter_data_size, -(int)abd->abd_size); ABDSTAT_INCR(abdstat_scatter_chunk_waste, -waste); arc_space_return(waste, ARC_SPACE_ABD_CHUNK_WASTE); } } void abd_update_linear_stats(abd_t *abd, abd_stats_op_t op) { ASSERT(op == ABDSTAT_INCR || op == ABDSTAT_DECR); if (op == ABDSTAT_INCR) { ABDSTAT_BUMP(abdstat_linear_cnt); ABDSTAT_INCR(abdstat_linear_data_size, abd->abd_size); } else { ABDSTAT_BUMPDOWN(abdstat_linear_cnt); ABDSTAT_INCR(abdstat_linear_data_size, -(int)abd->abd_size); } } void abd_verify_scatter(abd_t *abd) { ASSERT3U(ABD_SCATTER(abd).abd_nents, >, 0); ASSERT3U(ABD_SCATTER(abd).abd_offset, <, ABD_SCATTER(abd).abd_sgl->length); #ifdef ZFS_DEBUG struct scatterlist *sg = NULL; size_t n = ABD_SCATTER(abd).abd_nents; int i = 0; abd_for_each_sg(abd, sg, n, i) { ASSERT3P(sg_page(sg), !=, NULL); } #endif } static void abd_free_zero_scatter(void) { ABDSTAT_BUMPDOWN(abdstat_scatter_cnt); ABDSTAT_INCR(abdstat_scatter_data_size, -(int)PAGESIZE); ABDSTAT_BUMPDOWN(abdstat_scatter_page_multi_chunk); abd_free_sg_table(abd_zero_scatter); abd_free_struct(abd_zero_scatter); abd_zero_scatter = NULL; ASSERT3P(abd_zero_page, !=, NULL); #if defined(HAVE_ZERO_PAGE_GPL_ONLY) abd_unmark_zfs_page(abd_zero_page); __free_page(abd_zero_page); #endif /* HAVE_ZERO_PAGE_GPL_ONLY */ } static int abd_kstats_update(kstat_t *ksp, int rw) { abd_stats_t *as = ksp->ks_data; if (rw == KSTAT_WRITE) return (EACCES); as->abdstat_struct_size.value.ui64 = wmsum_value(&abd_sums.abdstat_struct_size); as->abdstat_linear_cnt.value.ui64 = wmsum_value(&abd_sums.abdstat_linear_cnt); as->abdstat_linear_data_size.value.ui64 = wmsum_value(&abd_sums.abdstat_linear_data_size); as->abdstat_scatter_cnt.value.ui64 = wmsum_value(&abd_sums.abdstat_scatter_cnt); as->abdstat_scatter_data_size.value.ui64 = wmsum_value(&abd_sums.abdstat_scatter_data_size); as->abdstat_scatter_chunk_waste.value.ui64 = wmsum_value(&abd_sums.abdstat_scatter_chunk_waste); for (int i = 0; i < ABD_MAX_ORDER; i++) { as->abdstat_scatter_orders[i].value.ui64 = wmsum_value(&abd_sums.abdstat_scatter_orders[i]); } as->abdstat_scatter_page_multi_chunk.value.ui64 = wmsum_value(&abd_sums.abdstat_scatter_page_multi_chunk); as->abdstat_scatter_page_multi_zone.value.ui64 = wmsum_value(&abd_sums.abdstat_scatter_page_multi_zone); as->abdstat_scatter_page_alloc_retry.value.ui64 = wmsum_value(&abd_sums.abdstat_scatter_page_alloc_retry); as->abdstat_scatter_sg_table_retry.value.ui64 = wmsum_value(&abd_sums.abdstat_scatter_sg_table_retry); return (0); } void abd_init(void) { int i; abd_cache = kmem_cache_create("abd_t", sizeof (abd_t), 0, NULL, NULL, NULL, NULL, NULL, KMC_RECLAIMABLE); wmsum_init(&abd_sums.abdstat_struct_size, 0); wmsum_init(&abd_sums.abdstat_linear_cnt, 0); wmsum_init(&abd_sums.abdstat_linear_data_size, 0); wmsum_init(&abd_sums.abdstat_scatter_cnt, 0); wmsum_init(&abd_sums.abdstat_scatter_data_size, 0); wmsum_init(&abd_sums.abdstat_scatter_chunk_waste, 0); for (i = 0; i < ABD_MAX_ORDER; i++) wmsum_init(&abd_sums.abdstat_scatter_orders[i], 0); wmsum_init(&abd_sums.abdstat_scatter_page_multi_chunk, 0); wmsum_init(&abd_sums.abdstat_scatter_page_multi_zone, 0); wmsum_init(&abd_sums.abdstat_scatter_page_alloc_retry, 0); wmsum_init(&abd_sums.abdstat_scatter_sg_table_retry, 0); abd_ksp = kstat_create("zfs", 0, "abdstats", "misc", KSTAT_TYPE_NAMED, sizeof (abd_stats) / sizeof (kstat_named_t), KSTAT_FLAG_VIRTUAL); if (abd_ksp != NULL) { for (i = 0; i < ABD_MAX_ORDER; i++) { snprintf(abd_stats.abdstat_scatter_orders[i].name, KSTAT_STRLEN, "scatter_order_%d", i); abd_stats.abdstat_scatter_orders[i].data_type = KSTAT_DATA_UINT64; } abd_ksp->ks_data = &abd_stats; abd_ksp->ks_update = abd_kstats_update; kstat_install(abd_ksp); } abd_alloc_zero_scatter(); } void abd_fini(void) { abd_free_zero_scatter(); if (abd_ksp != NULL) { kstat_delete(abd_ksp); abd_ksp = NULL; } wmsum_fini(&abd_sums.abdstat_struct_size); wmsum_fini(&abd_sums.abdstat_linear_cnt); wmsum_fini(&abd_sums.abdstat_linear_data_size); wmsum_fini(&abd_sums.abdstat_scatter_cnt); wmsum_fini(&abd_sums.abdstat_scatter_data_size); wmsum_fini(&abd_sums.abdstat_scatter_chunk_waste); for (int i = 0; i < ABD_MAX_ORDER; i++) wmsum_fini(&abd_sums.abdstat_scatter_orders[i]); wmsum_fini(&abd_sums.abdstat_scatter_page_multi_chunk); wmsum_fini(&abd_sums.abdstat_scatter_page_multi_zone); wmsum_fini(&abd_sums.abdstat_scatter_page_alloc_retry); wmsum_fini(&abd_sums.abdstat_scatter_sg_table_retry); if (abd_cache) { kmem_cache_destroy(abd_cache); abd_cache = NULL; } } void abd_free_linear_page(abd_t *abd) { /* Transform it back into a scatter ABD for freeing */ struct scatterlist *sg = abd->abd_u.abd_linear.abd_sgl; /* When backed by user page unmap it */ if (abd_is_from_pages(abd)) zfs_kunmap(sg_page(sg)); else abd_update_scatter_stats(abd, ABDSTAT_DECR); abd->abd_flags &= ~ABD_FLAG_LINEAR; abd->abd_flags &= ~ABD_FLAG_LINEAR_PAGE; ABD_SCATTER(abd).abd_nents = 1; ABD_SCATTER(abd).abd_offset = 0; ABD_SCATTER(abd).abd_sgl = sg; abd_free_chunks(abd); } /* * Allocate a scatter ABD structure from user pages. The pages must be * pinned with get_user_pages, or similiar, but need not be mapped via * the kmap interfaces. */ abd_t * abd_alloc_from_pages(struct page **pages, unsigned long offset, uint64_t size) { uint_t npages = DIV_ROUND_UP(size, PAGE_SIZE); struct sg_table table; VERIFY3U(size, <=, DMU_MAX_ACCESS); ASSERT3U(offset, <, PAGE_SIZE); ASSERT3P(pages, !=, NULL); /* * Even if this buf is filesystem metadata, we only track that we * own the underlying data buffer, which is not true in this case. * Therefore, we don't ever use ABD_FLAG_META here. */ abd_t *abd = abd_alloc_struct(0); abd->abd_flags |= ABD_FLAG_FROM_PAGES | ABD_FLAG_OWNER; abd->abd_size = size; while (sg_alloc_table_from_pages(&table, pages, npages, offset, size, __GFP_NOWARN | GFP_NOIO) != 0) { ABDSTAT_BUMP(abdstat_scatter_sg_table_retry); schedule_timeout_interruptible(1); } if ((offset + size) <= PAGE_SIZE) { /* * Since there is only one entry, this ABD can be represented * as a linear buffer. All single-page (4K) ABD's constructed * from a user page can be represented this way as long as the * page is mapped to a virtual address. This allows us to * apply an offset in to the mapped page. * * Note that kmap() must be used, not kmap_atomic(), because * the mapping needs to bet set up on all CPUs. Using kmap() * also enables the user of highmem pages when required. */ abd->abd_flags |= ABD_FLAG_LINEAR | ABD_FLAG_LINEAR_PAGE; abd->abd_u.abd_linear.abd_sgl = table.sgl; zfs_kmap(sg_page(table.sgl)); ABD_LINEAR_BUF(abd) = sg_virt(table.sgl); } else { ABDSTAT_BUMP(abdstat_scatter_page_multi_chunk); abd->abd_flags |= ABD_FLAG_MULTI_CHUNK; ABD_SCATTER(abd).abd_offset = offset; ABD_SCATTER(abd).abd_sgl = table.sgl; ABD_SCATTER(abd).abd_nents = table.nents; ASSERT0(ABD_SCATTER(abd).abd_offset); } return (abd); } /* * If we're going to use this ABD for doing I/O using the block layer, the * consumer of the ABD data doesn't care if it's scattered or not, and we don't * plan to store this ABD in memory for a long period of time, we should * allocate the ABD type that requires the least data copying to do the I/O. * * On Linux the optimal thing to do would be to use abd_get_offset() and * construct a new ABD which shares the original pages thereby eliminating * the copy. But for the moment a new linear ABD is allocated until this * performance optimization can be implemented. */ abd_t * abd_alloc_for_io(size_t size, boolean_t is_metadata) { return (abd_alloc(size, is_metadata)); } abd_t * abd_get_offset_scatter(abd_t *abd, abd_t *sabd, size_t off, size_t size) { (void) size; int i = 0; struct scatterlist *sg = NULL; abd_verify(sabd); ASSERT3U(off, <=, sabd->abd_size); size_t new_offset = ABD_SCATTER(sabd).abd_offset + off; if (abd == NULL) abd = abd_alloc_struct(0); /* * Even if this buf is filesystem metadata, we only track that * if we own the underlying data buffer, which is not true in * this case. Therefore, we don't ever use ABD_FLAG_META here. */ abd_for_each_sg(sabd, sg, ABD_SCATTER(sabd).abd_nents, i) { if (new_offset < sg->length) break; new_offset -= sg->length; } ABD_SCATTER(abd).abd_sgl = sg; ABD_SCATTER(abd).abd_offset = new_offset; ABD_SCATTER(abd).abd_nents = ABD_SCATTER(sabd).abd_nents - i; if (abd_is_from_pages(sabd)) abd->abd_flags |= ABD_FLAG_FROM_PAGES; return (abd); } /* * Initialize the abd_iter. */ void abd_iter_init(struct abd_iter *aiter, abd_t *abd) { ASSERT(!abd_is_gang(abd)); abd_verify(abd); memset(aiter, 0, sizeof (struct abd_iter)); aiter->iter_abd = abd; if (!abd_is_linear(abd)) { aiter->iter_offset = ABD_SCATTER(abd).abd_offset; aiter->iter_sg = ABD_SCATTER(abd).abd_sgl; } } /* * This is just a helper function to see if we have exhausted the * abd_iter and reached the end. */ boolean_t abd_iter_at_end(struct abd_iter *aiter) { ASSERT3U(aiter->iter_pos, <=, aiter->iter_abd->abd_size); return (aiter->iter_pos == aiter->iter_abd->abd_size); } /* * Advance the iterator by a certain amount. Cannot be called when a chunk is * in use. This can be safely called when the aiter has already exhausted, in * which case this does nothing. */ void abd_iter_advance(struct abd_iter *aiter, size_t amount) { /* * Ensure that last chunk is not in use. abd_iterate_*() must clear * this state (directly or abd_iter_unmap()) before advancing. */ ASSERT3P(aiter->iter_mapaddr, ==, NULL); ASSERT0(aiter->iter_mapsize); ASSERT3P(aiter->iter_page, ==, NULL); ASSERT0(aiter->iter_page_doff); ASSERT0(aiter->iter_page_dsize); /* There's nothing left to advance to, so do nothing */ if (abd_iter_at_end(aiter)) return; aiter->iter_pos += amount; aiter->iter_offset += amount; if (!abd_is_linear(aiter->iter_abd)) { while (aiter->iter_offset >= aiter->iter_sg->length) { aiter->iter_offset -= aiter->iter_sg->length; aiter->iter_sg = sg_next(aiter->iter_sg); if (aiter->iter_sg == NULL) { ASSERT0(aiter->iter_offset); break; } } } } /* * Map the current chunk into aiter. This can be safely called when the aiter * has already exhausted, in which case this does nothing. */ void abd_iter_map(struct abd_iter *aiter) { void *paddr; size_t offset = 0; ASSERT3P(aiter->iter_mapaddr, ==, NULL); ASSERT0(aiter->iter_mapsize); /* There's nothing left to iterate over, so do nothing */ if (abd_iter_at_end(aiter)) return; if (abd_is_linear(aiter->iter_abd)) { ASSERT3U(aiter->iter_pos, ==, aiter->iter_offset); offset = aiter->iter_offset; aiter->iter_mapsize = aiter->iter_abd->abd_size - offset; paddr = ABD_LINEAR_BUF(aiter->iter_abd); } else { offset = aiter->iter_offset; aiter->iter_mapsize = MIN(aiter->iter_sg->length - offset, aiter->iter_abd->abd_size - aiter->iter_pos); paddr = zfs_kmap_local(sg_page(aiter->iter_sg)); } aiter->iter_mapaddr = (char *)paddr + offset; } /* * Unmap the current chunk from aiter. This can be safely called when the aiter * has already exhausted, in which case this does nothing. */ void abd_iter_unmap(struct abd_iter *aiter) { /* There's nothing left to unmap, so do nothing */ if (abd_iter_at_end(aiter)) return; if (!abd_is_linear(aiter->iter_abd)) { /* LINTED E_FUNC_SET_NOT_USED */ zfs_kunmap_local(aiter->iter_mapaddr - aiter->iter_offset); } ASSERT3P(aiter->iter_mapaddr, !=, NULL); ASSERT3U(aiter->iter_mapsize, >, 0); aiter->iter_mapaddr = NULL; aiter->iter_mapsize = 0; } void abd_cache_reap_now(void) { } /* * Borrow a raw buffer from an ABD without copying the contents of the ABD * into the buffer. If the ABD is scattered, this will allocate a raw buffer * whose contents are undefined. To copy over the existing data in the ABD, use * abd_borrow_buf_copy() instead. */ void * abd_borrow_buf(abd_t *abd, size_t n) { void *buf; abd_verify(abd); ASSERT3U(abd->abd_size, >=, 0); /* * In the event the ABD is composed of a single user page from Direct * I/O we can not direclty return the raw buffer. This is a consequence * of not being able to write protect the page and the contents of the * page can be changed at any time by the user. */ if (abd_is_from_pages(abd)) { buf = zio_buf_alloc(n); } else if (abd_is_linear(abd)) { buf = abd_to_buf(abd); } else { buf = zio_buf_alloc(n); } #ifdef ZFS_DEBUG (void) zfs_refcount_add_many(&abd->abd_children, n, buf); #endif return (buf); } void * abd_borrow_buf_copy(abd_t *abd, size_t n) { void *buf = abd_borrow_buf(abd, n); /* * In the event the ABD is composed of a single user page from Direct * I/O we must make sure copy the data over into the newly allocated * buffer. This is a consequence of the fact that we can not write * protect the user page and there is a risk the contents of the page * could be changed by the user at any moment. */ if (!abd_is_linear(abd) || abd_is_from_pages(abd)) { abd_copy_to_buf(buf, abd, n); } return (buf); } /* * Return a borrowed raw buffer to an ABD. If the ABD is scatterd, this will * not change the contents of the ABD. If you want any changes you made to * buf to be copied back to abd, use abd_return_buf_copy() instead. If the * ABD is not constructed from user pages for Direct I/O then an ASSERT * checks to make sure the contents of buffer have not changed since it was * borrowed. We can not ASSERT that the contents of the buffer have not changed * if it is composed of user pages because the pages can not be placed under * write protection and the user could have possibly changed the contents in * the pages at any time. This is also an issue for Direct I/O reads. Checksum * verifications in the ZIO pipeline check for this issue and handle it by * returning an error on checksum verification failure. */ void abd_return_buf(abd_t *abd, void *buf, size_t n) { abd_verify(abd); ASSERT3U(abd->abd_size, >=, n); #ifdef ZFS_DEBUG (void) zfs_refcount_remove_many(&abd->abd_children, n, buf); #endif if (abd_is_from_pages(abd)) { zio_buf_free(buf, n); } else if (abd_is_linear(abd)) { ASSERT3P(buf, ==, abd_to_buf(abd)); } else if (abd_is_gang(abd)) { #ifdef ZFS_DEBUG /* * We have to be careful with gang ABD's that we do not ASSERT0 * for any ABD's that contain user pages from Direct I/O. In * order to handle this, we just iterate through the gang ABD * and only verify ABDs that are not from user pages. */ void *cmp_buf = buf; for (abd_t *cabd = list_head(&ABD_GANG(abd).abd_gang_chain); cabd != NULL; cabd = list_next(&ABD_GANG(abd).abd_gang_chain, cabd)) { if (!abd_is_from_pages(cabd)) { ASSERT0(abd_cmp_buf(cabd, cmp_buf, cabd->abd_size)); } cmp_buf = (char *)cmp_buf + cabd->abd_size; } #endif zio_buf_free(buf, n); } else { ASSERT0(abd_cmp_buf(abd, buf, n)); zio_buf_free(buf, n); } } void abd_return_buf_copy(abd_t *abd, void *buf, size_t n) { if (!abd_is_linear(abd) || abd_is_from_pages(abd)) { abd_copy_from_buf(abd, buf, n); } abd_return_buf(abd, buf, n); } /* * This is abd_iter_page(), the function underneath abd_iterate_page_func(). * It yields the next page struct and data offset and size within it, without * mapping it into the address space. */ /* * "Compound pages" are a group of pages that can be referenced from a single * struct page *. Its organised as a "head" page, followed by a series of * "tail" pages. * * In OpenZFS, compound pages are allocated using the __GFP_COMP flag, which we * get from scatter ABDs and SPL vmalloc slabs (ie >16K allocations). So a * great many of the IO buffers we get are going to be of this type. * * The tail pages are just regular PAGESIZE pages, and can be safely used * as-is. However, the head page has length covering itself and all the tail * pages. If the ABD chunk spans multiple pages, then we can use the head page * and a >PAGESIZE length, which is far more efficient. * * Before kernel 4.5 however, compound page heads were refcounted separately * from tail pages, such that moving back to the head page would require us to * take a reference to it and releasing it once we're completely finished with * it. In practice, that meant when our caller is done with the ABD, which we * have no insight into from here. Rather than contort this API to track head * page references on such ancient kernels, we disabled this special compound * page handling on kernels before 4.5, instead just using treating each page * within it as a regular PAGESIZE page (which it is). This is slightly less * efficient, but makes everything far simpler. * * We no longer support kernels before 4.5, so in theory none of this is * necessary. However, this code is still relatively new in the grand scheme of * things, so I'm leaving the ability to compile this out for the moment. * * Setting/clearing ABD_ITER_COMPOUND_PAGES below enables/disables the special * handling, by defining the ABD_ITER_PAGE_SIZE(page) macro to understand * compound pages, or not, and compiling in/out the support to detect compound * tail pages and move back to the start. */ /* On by default */ #define ABD_ITER_COMPOUND_PAGES #ifdef ABD_ITER_COMPOUND_PAGES #define ABD_ITER_PAGE_SIZE(page) \ (PageCompound(page) ? page_size(page) : PAGESIZE) #else #define ABD_ITER_PAGE_SIZE(page) (PAGESIZE) #endif void abd_iter_page(struct abd_iter *aiter) { if (abd_iter_at_end(aiter)) { aiter->iter_page = NULL; aiter->iter_page_doff = 0; aiter->iter_page_dsize = 0; return; } struct page *page; size_t doff, dsize; /* * Find the page, and the start of the data within it. This is computed * differently for linear and scatter ABDs; linear is referenced by * virtual memory location, while scatter is referenced by page * pointer. */ if (abd_is_linear(aiter->iter_abd)) { ASSERT3U(aiter->iter_pos, ==, aiter->iter_offset); /* memory address at iter_pos */ void *paddr = ABD_LINEAR_BUF(aiter->iter_abd) + aiter->iter_pos; /* struct page for address */ page = is_vmalloc_addr(paddr) ? vmalloc_to_page(paddr) : virt_to_page(paddr); /* offset of address within the page */ doff = offset_in_page(paddr); } else { ASSERT(!abd_is_gang(aiter->iter_abd)); /* current scatter page */ page = nth_page(sg_page(aiter->iter_sg), aiter->iter_offset >> PAGE_SHIFT); /* position within page */ doff = aiter->iter_offset & (PAGESIZE - 1); } #ifdef ABD_ITER_COMPOUND_PAGES if (PageTail(page)) { /* * If this is a compound tail page, move back to the head, and * adjust the offset to match. This may let us yield a much * larger amount of data from a single logical page, and so * leave our caller with fewer pages to process. */ struct page *head = compound_head(page); doff += ((page - head) * PAGESIZE); page = head; } #endif ASSERT(page); /* * Compute the maximum amount of data we can take from this page. This * is the smaller of: * - the remaining space in the page * - the remaining space in this scatterlist entry (which may not cover * the entire page) * - the remaining space in the abd (which may not cover the entire * scatterlist entry) */ dsize = MIN(ABD_ITER_PAGE_SIZE(page) - doff, aiter->iter_abd->abd_size - aiter->iter_pos); if (!abd_is_linear(aiter->iter_abd)) dsize = MIN(dsize, aiter->iter_sg->length - aiter->iter_offset); ASSERT3U(dsize, >, 0); /* final iterator outputs */ aiter->iter_page = page; aiter->iter_page_doff = doff; aiter->iter_page_dsize = dsize; } /* * Note: ABD BIO functions only needed to support vdev_classic. See comments in * vdev_disk.c. */ /* * bio_nr_pages for ABD. * @off is the offset in @abd */ unsigned long abd_nr_pages_off(abd_t *abd, unsigned int size, size_t off) { unsigned long pos; if (abd_is_gang(abd)) { unsigned long count = 0; for (abd_t *cabd = abd_gang_get_offset(abd, &off); cabd != NULL && size != 0; cabd = list_next(&ABD_GANG(abd).abd_gang_chain, cabd)) { ASSERT3U(off, <, cabd->abd_size); int mysize = MIN(size, cabd->abd_size - off); count += abd_nr_pages_off(cabd, mysize, off); size -= mysize; off = 0; } return (count); } if (abd_is_linear(abd)) pos = (unsigned long)abd_to_buf(abd) + off; else pos = ABD_SCATTER(abd).abd_offset + off; return (((pos + size + PAGESIZE - 1) >> PAGE_SHIFT) - (pos >> PAGE_SHIFT)); } static unsigned int bio_map(struct bio *bio, void *buf_ptr, unsigned int bio_size) { unsigned int offset, size, i; struct page *page; offset = offset_in_page(buf_ptr); for (i = 0; i < bio->bi_max_vecs; i++) { size = PAGE_SIZE - offset; if (bio_size <= 0) break; if (size > bio_size) size = bio_size; if (is_vmalloc_addr(buf_ptr)) page = vmalloc_to_page(buf_ptr); else page = virt_to_page(buf_ptr); /* * Some network related block device uses tcp_sendpage, which * doesn't behave well when using 0-count page, this is a * safety net to catch them. */ ASSERT3S(page_count(page), >, 0); if (bio_add_page(bio, page, size, offset) != size) break; buf_ptr += size; bio_size -= size; offset = 0; } return (bio_size); } /* * bio_map for gang ABD. */ static unsigned int abd_gang_bio_map_off(struct bio *bio, abd_t *abd, unsigned int io_size, size_t off) { ASSERT(abd_is_gang(abd)); for (abd_t *cabd = abd_gang_get_offset(abd, &off); cabd != NULL; cabd = list_next(&ABD_GANG(abd).abd_gang_chain, cabd)) { ASSERT3U(off, <, cabd->abd_size); int size = MIN(io_size, cabd->abd_size - off); int remainder = abd_bio_map_off(bio, cabd, size, off); io_size -= (size - remainder); if (io_size == 0 || remainder > 0) return (io_size); off = 0; } ASSERT0(io_size); return (io_size); } /* * bio_map for ABD. * @off is the offset in @abd * Remaining IO size is returned */ unsigned int abd_bio_map_off(struct bio *bio, abd_t *abd, unsigned int io_size, size_t off) { struct abd_iter aiter; ASSERT3U(io_size, <=, abd->abd_size - off); if (abd_is_linear(abd)) return (bio_map(bio, ((char *)abd_to_buf(abd)) + off, io_size)); ASSERT(!abd_is_linear(abd)); if (abd_is_gang(abd)) return (abd_gang_bio_map_off(bio, abd, io_size, off)); abd_iter_init(&aiter, abd); abd_iter_advance(&aiter, off); for (int i = 0; i < bio->bi_max_vecs; i++) { struct page *pg; size_t len, sgoff, pgoff; struct scatterlist *sg; if (io_size <= 0) break; sg = aiter.iter_sg; sgoff = aiter.iter_offset; pgoff = sgoff & (PAGESIZE - 1); len = MIN(io_size, PAGESIZE - pgoff); ASSERT(len > 0); pg = nth_page(sg_page(sg), sgoff >> PAGE_SHIFT); if (bio_add_page(bio, pg, len, pgoff) != len) break; io_size -= len; abd_iter_advance(&aiter, len); } return (io_size); } /* Tunable Parameters */ module_param(zfs_abd_scatter_enabled, int, 0644); MODULE_PARM_DESC(zfs_abd_scatter_enabled, "Toggle whether ABD allocations must be linear."); module_param(zfs_abd_scatter_min_size, int, 0644); MODULE_PARM_DESC(zfs_abd_scatter_min_size, "Minimum size of scatter allocations."); module_param(zfs_abd_scatter_max_order, uint, 0644); MODULE_PARM_DESC(zfs_abd_scatter_max_order, "Maximum order allocation used for a scatter ABD.");