linux/zfs/arc_os.c

/*
 * 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 (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
 * Copyright (c) 2018, Joyent, Inc.
 * Copyright (c) 2011, 2019 by Delphix. All rights reserved.
 * Copyright (c) 2014 by Saso Kiselkov. All rights reserved.
 * Copyright 2017 Nexenta Systems, Inc.  All rights reserved.
 */

#include <sys/spa.h>
#include <sys/zio.h>
#include <sys/spa_impl.h>
#include <sys/zio_compress.h>
#include <sys/zio_checksum.h>
#include <sys/zfs_context.h>
#include <sys/arc.h>
#include <sys/zfs_refcount.h>
#include <sys/vdev.h>
#include <sys/vdev_trim.h>
#include <sys/vdev_impl.h>
#include <sys/dsl_pool.h>
#include <sys/zio_checksum.h>
#include <sys/multilist.h>
#include <sys/abd.h>
#include <sys/zil.h>
#include <sys/fm/fs/zfs.h>
#ifdef _KERNEL
#include <sys/shrinker.h>
#include <sys/vmsystm.h>
#include <sys/zpl.h>
#include <linux/page_compat.h>
#endif
#include <sys/callb.h>
#include <sys/kstat.h>
#include <sys/zthr.h>
#include <zfs_fletcher.h>
#include <sys/arc_impl.h>
#include <sys/trace_zfs.h>
#include <sys/aggsum.h>

/*
 * This is a limit on how many pages the ARC shrinker makes available for
 * eviction in response to one page allocation attempt.  Note that in
 * practice, the kernel's shrinker can ask us to evict up to about 4x this
 * for one allocation attempt.
 *
 * The default limit of 10,000 (in practice, 160MB per allocation attempt
 * with 4K pages) limits the amount of time spent attempting to reclaim ARC
 * memory to less than 100ms per allocation attempt, even with a small
 * average compressed block size of ~8KB.
 *
 * See also the comment in arc_shrinker_count().
 * Set to 0 to disable limit.
 */
int zfs_arc_shrinker_limit = 10000;


/*
 * Return a default max arc size based on the amount of physical memory.
 */
uint64_t
arc_default_max(uint64_t min, uint64_t allmem)
{
	/* Default to 1/2 of all memory. */
	return (MAX(allmem / 2, min));
}

#ifdef _KERNEL
/*
 * Return maximum amount of memory that we could possibly use.  Reduced
 * to half of all memory in user space which is primarily used for testing.
 */
uint64_t
arc_all_memory(void)
{
#ifdef CONFIG_HIGHMEM
	return (ptob(zfs_totalram_pages - zfs_totalhigh_pages));
#else
	return (ptob(zfs_totalram_pages));
#endif /* CONFIG_HIGHMEM */
}

/*
 * Return the amount of memory that is considered free.  In user space
 * which is primarily used for testing we pretend that free memory ranges
 * from 0-20% of all memory.
 */
uint64_t
arc_free_memory(void)
{
#ifdef CONFIG_HIGHMEM
	struct sysinfo si;
	si_meminfo(&si);
	return (ptob(si.freeram - si.freehigh));
#else
	return (ptob(nr_free_pages() +
	    nr_inactive_file_pages()));
#endif /* CONFIG_HIGHMEM */
}

/*
 * Return the amount of memory that can be consumed before reclaim will be
 * needed.  Positive if there is sufficient free memory, negative indicates
 * the amount of memory that needs to be freed up.
 */
int64_t
arc_available_memory(void)
{
	return (arc_free_memory() - arc_sys_free);
}

static uint64_t
arc_evictable_memory(void)
{
	int64_t asize = aggsum_value(&arc_size);
	uint64_t arc_clean =
	    zfs_refcount_count(&arc_mru->arcs_esize[ARC_BUFC_DATA]) +
	    zfs_refcount_count(&arc_mru->arcs_esize[ARC_BUFC_METADATA]) +
	    zfs_refcount_count(&arc_mfu->arcs_esize[ARC_BUFC_DATA]) +
	    zfs_refcount_count(&arc_mfu->arcs_esize[ARC_BUFC_METADATA]);
	uint64_t arc_dirty = MAX((int64_t)asize - (int64_t)arc_clean, 0);

	/*
	 * Scale reported evictable memory in proportion to page cache, cap
	 * at specified min/max.
	 */
	uint64_t min = (ptob(nr_file_pages()) / 100) * zfs_arc_pc_percent;
	min = MAX(arc_c_min, MIN(arc_c_max, min));

	if (arc_dirty >= min)
		return (arc_clean);

	return (MAX((int64_t)asize - (int64_t)min, 0));
}

/*
 * The _count() function returns the number of free-able objects.
 * The _scan() function returns the number of objects that were freed.
 */
static unsigned long
arc_shrinker_count(struct shrinker *shrink, struct shrink_control *sc)
{
	/*
	 * __GFP_FS won't be set if we are called from ZFS code (see
	 * kmem_flags_convert(), which removes it).  To avoid a deadlock, we
	 * don't allow evicting in this case.  We return 0 rather than
	 * SHRINK_STOP so that the shrinker logic doesn't accumulate a
	 * deficit against us.
	 */
	if (!(sc->gfp_mask & __GFP_FS)) {
		return (0);
	}

	/*
	 * This code is reached in the "direct reclaim" case, where the
	 * kernel (outside ZFS) is trying to allocate a page, and the system
	 * is low on memory.
	 *
	 * The kernel's shrinker code doesn't understand how many pages the
	 * ARC's callback actually frees, so it may ask the ARC to shrink a
	 * lot for one page allocation. This is problematic because it may
	 * take a long time, thus delaying the page allocation, and because
	 * it may force the ARC to unnecessarily shrink very small.
	 *
	 * Therefore, we limit the amount of data that we say is evictable,
	 * which limits the amount that the shrinker will ask us to evict for
	 * one page allocation attempt.
	 *
	 * In practice, we may be asked to shrink 4x the limit to satisfy one
	 * page allocation, before the kernel's shrinker code gives up on us.
	 * When that happens, we rely on the kernel code to find the pages
	 * that we freed before invoking the OOM killer.  This happens in
	 * __alloc_pages_slowpath(), which retries and finds the pages we
	 * freed when it calls get_page_from_freelist().
	 *
	 * See also the comment above zfs_arc_shrinker_limit.
	 */
	int64_t limit = zfs_arc_shrinker_limit != 0 ?
	    zfs_arc_shrinker_limit : INT64_MAX;
	return (MIN(limit, btop((int64_t)arc_evictable_memory())));
}

static unsigned long
arc_shrinker_scan(struct shrinker *shrink, struct shrink_control *sc)
{
	ASSERT((sc->gfp_mask & __GFP_FS) != 0);

	/* The arc is considered warm once reclaim has occurred */
	if (unlikely(arc_warm == B_FALSE))
		arc_warm = B_TRUE;

	/*
	 * Evict the requested number of pages by reducing arc_c and waiting
	 * for the requested amount of data to be evicted.
	 */
	arc_reduce_target_size(ptob(sc->nr_to_scan));
	arc_wait_for_eviction(ptob(sc->nr_to_scan));
	if (current->reclaim_state != NULL)
		current->reclaim_state->reclaimed_slab += sc->nr_to_scan;

	/*
	 * We are experiencing memory pressure which the arc_evict_zthr was
	 * unable to keep up with. Set arc_no_grow to briefly pause arc
	 * growth to avoid compounding the memory pressure.
	 */
	arc_no_grow = B_TRUE;

	/*
	 * When direct reclaim is observed it usually indicates a rapid
	 * increase in memory pressure.  This occurs because the kswapd
	 * threads were unable to asynchronously keep enough free memory
	 * available.
	 */
	if (current_is_kswapd()) {
		ARCSTAT_BUMP(arcstat_memory_indirect_count);
	} else {
		ARCSTAT_BUMP(arcstat_memory_direct_count);
	}

	return (sc->nr_to_scan);
}

SPL_SHRINKER_DECLARE(arc_shrinker,
    arc_shrinker_count, arc_shrinker_scan, DEFAULT_SEEKS);

int
arc_memory_throttle(spa_t *spa, uint64_t reserve, uint64_t txg)
{
	uint64_t free_memory = arc_free_memory();

	if (free_memory > arc_all_memory() * arc_lotsfree_percent / 100)
		return (0);

	if (txg > spa->spa_lowmem_last_txg) {
		spa->spa_lowmem_last_txg = txg;
		spa->spa_lowmem_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 (current_is_kswapd()) {
		if (spa->spa_lowmem_page_load >
		    MAX(arc_sys_free / 4, free_memory) / 4) {
			DMU_TX_STAT_BUMP(dmu_tx_memory_reclaim);
			return (SET_ERROR(ERESTART));
		}
		/* Note: reserve is inflated, so we deflate */
		atomic_add_64(&spa->spa_lowmem_page_load, reserve / 8);
		return (0);
	} else if (spa->spa_lowmem_page_load > 0 && arc_reclaim_needed()) {
		/* memory is low, delay before restarting */
		ARCSTAT_INCR(arcstat_memory_throttle_count, 1);
		DMU_TX_STAT_BUMP(dmu_tx_memory_reclaim);
		return (SET_ERROR(EAGAIN));
	}
	spa->spa_lowmem_page_load = 0;
	return (0);
}

void
arc_lowmem_init(void)
{
	uint64_t allmem = arc_all_memory();

	/*
	 * Register a shrinker to support synchronous (direct) memory
	 * reclaim from the arc.  This is done to prevent kswapd from
	 * swapping out pages when it is preferable to shrink the arc.
	 */
	spl_register_shrinker(&arc_shrinker);

	/*
	 * The ARC tries to keep at least this much memory available for the
	 * system.  This gives the ARC time to shrink in response to memory
	 * pressure, before running completely out of memory and invoking the
	 * direct-reclaim ARC shrinker.
	 *
	 * This should be more than twice high_wmark_pages(), so that
	 * arc_wait_for_eviction() will wait until at least the
	 * high_wmark_pages() are free (see arc_evict_state_impl()).
	 *
	 * Note: Even when the system is very low on memory, the kernel's
	 * shrinker code may only ask for one "batch" of pages (512KB) to be
	 * evicted.  If concurrent allocations consume these pages, there may
	 * still be insufficient free pages, and the OOM killer takes action.
	 *
	 * By setting arc_sys_free large enough, and having
	 * arc_wait_for_eviction() wait until there is at least arc_sys_free/2
	 * free memory, it is much less likely that concurrent allocations can
	 * consume all the memory that was evicted before checking for
	 * OOM.
	 *
	 * It's hard to iterate the zones from a linux kernel module, which
	 * makes it difficult to determine the watermark dynamically. Instead
	 * we compute the maximum high watermark for this system, based
	 * on the amount of memory, assuming default parameters on Linux kernel
	 * 5.3.
	 */

	/*
	 * Base wmark_low is 4 * the square root of Kbytes of RAM.
	 */
	long wmark = 4 * int_sqrt(allmem/1024) * 1024;

	/*
	 * Clamp to between 128K and 64MB.
	 */
	wmark = MAX(wmark, 128 * 1024);
	wmark = MIN(wmark, 64 * 1024 * 1024);

	/*
	 * watermark_boost can increase the wmark by up to 150%.
	 */
	wmark += wmark * 150 / 100;

	/*
	 * arc_sys_free needs to be more than 2x the watermark, because
	 * arc_wait_for_eviction() waits for half of arc_sys_free.  Bump this up
	 * to 3x to ensure we're above it.
	 */
	arc_sys_free = wmark * 3 + allmem / 32;
}

void
arc_lowmem_fini(void)
{
	spl_unregister_shrinker(&arc_shrinker);
}

int
param_set_arc_long(const char *buf, zfs_kernel_param_t *kp)
{
	int error;

	error = param_set_long(buf, kp);
	if (error < 0)
		return (SET_ERROR(error));

	arc_tuning_update(B_TRUE);

	return (0);
}

int
param_set_arc_int(const char *buf, zfs_kernel_param_t *kp)
{
	int error;

	error = param_set_int(buf, kp);
	if (error < 0)
		return (SET_ERROR(error));

	arc_tuning_update(B_TRUE);

	return (0);
}
#else /* _KERNEL */
int64_t
arc_available_memory(void)
{
	int64_t lowest = INT64_MAX;

	/* Every 100 calls, free a small amount */
	if (spa_get_random(100) == 0)
		lowest = -1024;

	return (lowest);
}

int
arc_memory_throttle(spa_t *spa, uint64_t reserve, uint64_t txg)
{
	return (0);
}

uint64_t
arc_all_memory(void)
{
	return (ptob(physmem) / 2);
}

uint64_t
arc_free_memory(void)
{
	return (spa_get_random(arc_all_memory() * 20 / 100));
}
#endif /* _KERNEL */

/*
 * Helper function for arc_prune_async() it is responsible for safely
 * handling the execution of a registered arc_prune_func_t.
 */
static void
arc_prune_task(void *ptr)
{
	arc_prune_t *ap = (arc_prune_t *)ptr;
	arc_prune_func_t *func = ap->p_pfunc;

	if (func != NULL)
		func(ap->p_adjust, ap->p_private);

	zfs_refcount_remove(&ap->p_refcnt, func);
}

/*
 * Notify registered consumers they must drop holds on a portion of the ARC
 * buffered they reference.  This provides a mechanism to ensure the ARC can
 * honor the arc_meta_limit and reclaim otherwise pinned ARC buffers.  This
 * is analogous to dnlc_reduce_cache() but more generic.
 *
 * This operation is performed asynchronously so it may be safely called
 * in the context of the arc_reclaim_thread().  A reference is taken here
 * for each registered arc_prune_t and the arc_prune_task() is responsible
 * for releasing it once the registered arc_prune_func_t has completed.
 */
void
arc_prune_async(int64_t adjust)
{
	arc_prune_t *ap;

	mutex_enter(&arc_prune_mtx);
	for (ap = list_head(&arc_prune_list); ap != NULL;
	    ap = list_next(&arc_prune_list, ap)) {

		if (zfs_refcount_count(&ap->p_refcnt) >= 2)
			continue;

		zfs_refcount_add(&ap->p_refcnt, ap->p_pfunc);
		ap->p_adjust = adjust;
		if (taskq_dispatch(arc_prune_taskq, arc_prune_task,
		    ap, TQ_SLEEP) == TASKQID_INVALID) {
			zfs_refcount_remove(&ap->p_refcnt, ap->p_pfunc);
			continue;
		}
		ARCSTAT_BUMP(arcstat_prune);
	}
	mutex_exit(&arc_prune_mtx);
}

/* BEGIN CSTYLED */
ZFS_MODULE_PARAM(zfs_arc, zfs_arc_, shrinker_limit, INT, ZMOD_RW,
	"Limit on number of pages that ARC shrinker can reclaim at once");
/* END CSTYLED */