blob: e04f4476e68e8a8409960d6d4f5de28495ef5f02 [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0
/*
* linux/mm/compaction.c
*
* Memory compaction for the reduction of external fragmentation. Note that
* this heavily depends upon page migration to do all the real heavy
* lifting
*
* Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
*/
#include <linux/cpu.h>
#include <linux/swap.h>
#include <linux/migrate.h>
#include <linux/compaction.h>
#include <linux/mm_inline.h>
#include <linux/sched/signal.h>
#include <linux/backing-dev.h>
#include <linux/sysctl.h>
#include <linux/sysfs.h>
#include <linux/page-isolation.h>
#include <linux/kasan.h>
#include <linux/kthread.h>
#include <linux/freezer.h>
#include <linux/page_owner.h>
#include <linux/psi.h>
#include "internal.h"
#ifdef CONFIG_COMPACTION
static inline void count_compact_event(enum vm_event_item item)
{
count_vm_event(item);
}
static inline void count_compact_events(enum vm_event_item item, long delta)
{
count_vm_events(item, delta);
}
#else
#define count_compact_event(item) do { } while (0)
#define count_compact_events(item, delta) do { } while (0)
#endif
#if defined CONFIG_COMPACTION || defined CONFIG_CMA
#define CREATE_TRACE_POINTS
#include <trace/events/compaction.h>
#define block_start_pfn(pfn, order) round_down(pfn, 1UL << (order))
#define block_end_pfn(pfn, order) ALIGN((pfn) + 1, 1UL << (order))
#define pageblock_start_pfn(pfn) block_start_pfn(pfn, pageblock_order)
#define pageblock_end_pfn(pfn) block_end_pfn(pfn, pageblock_order)
/*
* Fragmentation score check interval for proactive compaction purposes.
*/
static const unsigned int HPAGE_FRAG_CHECK_INTERVAL_MSEC = 500;
/*
* Page order with-respect-to which proactive compaction
* calculates external fragmentation, which is used as
* the "fragmentation score" of a node/zone.
*/
#if defined CONFIG_TRANSPARENT_HUGEPAGE
#define COMPACTION_HPAGE_ORDER HPAGE_PMD_ORDER
#elif defined CONFIG_HUGETLBFS
#define COMPACTION_HPAGE_ORDER HUGETLB_PAGE_ORDER
#else
#define COMPACTION_HPAGE_ORDER (PMD_SHIFT - PAGE_SHIFT)
#endif
static unsigned long release_freepages(struct list_head *freelist)
{
struct page *page, *next;
unsigned long high_pfn = 0;
list_for_each_entry_safe(page, next, freelist, lru) {
unsigned long pfn = page_to_pfn(page);
list_del(&page->lru);
__free_page(page);
if (pfn > high_pfn)
high_pfn = pfn;
}
return high_pfn;
}
static void split_map_pages(struct list_head *list)
{
unsigned int i, order, nr_pages;
struct page *page, *next;
LIST_HEAD(tmp_list);
list_for_each_entry_safe(page, next, list, lru) {
list_del(&page->lru);
order = page_private(page);
nr_pages = 1 << order;
post_alloc_hook(page, order, __GFP_MOVABLE);
if (order)
split_page(page, order);
for (i = 0; i < nr_pages; i++) {
list_add(&page->lru, &tmp_list);
page++;
}
}
list_splice(&tmp_list, list);
}
#ifdef CONFIG_COMPACTION
int PageMovable(struct page *page)
{
struct address_space *mapping;
VM_BUG_ON_PAGE(!PageLocked(page), page);
if (!__PageMovable(page))
return 0;
mapping = page_mapping(page);
if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
return 1;
return 0;
}
EXPORT_SYMBOL(PageMovable);
void __SetPageMovable(struct page *page, struct address_space *mapping)
{
VM_BUG_ON_PAGE(!PageLocked(page), page);
VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
}
EXPORT_SYMBOL(__SetPageMovable);
void __ClearPageMovable(struct page *page)
{
VM_BUG_ON_PAGE(!PageMovable(page), page);
/*
* Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
* flag so that VM can catch up released page by driver after isolation.
* With it, VM migration doesn't try to put it back.
*/
page->mapping = (void *)((unsigned long)page->mapping &
PAGE_MAPPING_MOVABLE);
}
EXPORT_SYMBOL(__ClearPageMovable);
/* Do not skip compaction more than 64 times */
#define COMPACT_MAX_DEFER_SHIFT 6
/*
* Compaction is deferred when compaction fails to result in a page
* allocation success. 1 << compact_defer_shift, compactions are skipped up
* to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
*/
static void defer_compaction(struct zone *zone, int order)
{
zone->compact_considered = 0;
zone->compact_defer_shift++;
if (order < zone->compact_order_failed)
zone->compact_order_failed = order;
if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
trace_mm_compaction_defer_compaction(zone, order);
}
/* Returns true if compaction should be skipped this time */
static bool compaction_deferred(struct zone *zone, int order)
{
unsigned long defer_limit = 1UL << zone->compact_defer_shift;
if (order < zone->compact_order_failed)
return false;
/* Avoid possible overflow */
if (++zone->compact_considered >= defer_limit) {
zone->compact_considered = defer_limit;
return false;
}
trace_mm_compaction_deferred(zone, order);
return true;
}
/*
* Update defer tracking counters after successful compaction of given order,
* which means an allocation either succeeded (alloc_success == true) or is
* expected to succeed.
*/
void compaction_defer_reset(struct zone *zone, int order,
bool alloc_success)
{
if (alloc_success) {
zone->compact_considered = 0;
zone->compact_defer_shift = 0;
}
if (order >= zone->compact_order_failed)
zone->compact_order_failed = order + 1;
trace_mm_compaction_defer_reset(zone, order);
}
/* Returns true if restarting compaction after many failures */
static bool compaction_restarting(struct zone *zone, int order)
{
if (order < zone->compact_order_failed)
return false;
return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
zone->compact_considered >= 1UL << zone->compact_defer_shift;
}
/* Returns true if the pageblock should be scanned for pages to isolate. */
static inline bool isolation_suitable(struct compact_control *cc,
struct page *page)
{
if (cc->ignore_skip_hint)
return true;
return !get_pageblock_skip(page);
}
static void reset_cached_positions(struct zone *zone)
{
zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
zone->compact_cached_free_pfn =
pageblock_start_pfn(zone_end_pfn(zone) - 1);
}
/*
* Compound pages of >= pageblock_order should consistently be skipped until
* released. It is always pointless to compact pages of such order (if they are
* migratable), and the pageblocks they occupy cannot contain any free pages.
*/
static bool pageblock_skip_persistent(struct page *page)
{
if (!PageCompound(page))
return false;
page = compound_head(page);
if (compound_order(page) >= pageblock_order)
return true;
return false;
}
static bool
__reset_isolation_pfn(struct zone *zone, unsigned long pfn, bool check_source,
bool check_target)
{
struct page *page = pfn_to_online_page(pfn);
struct page *block_page;
struct page *end_page;
unsigned long block_pfn;
if (!page)
return false;
if (zone != page_zone(page))
return false;
if (pageblock_skip_persistent(page))
return false;
/*
* If skip is already cleared do no further checking once the
* restart points have been set.
*/
if (check_source && check_target && !get_pageblock_skip(page))
return true;
/*
* If clearing skip for the target scanner, do not select a
* non-movable pageblock as the starting point.
*/
if (!check_source && check_target &&
get_pageblock_migratetype(page) != MIGRATE_MOVABLE)
return false;
/* Ensure the start of the pageblock or zone is online and valid */
block_pfn = pageblock_start_pfn(pfn);
block_pfn = max(block_pfn, zone->zone_start_pfn);
block_page = pfn_to_online_page(block_pfn);
if (block_page) {
page = block_page;
pfn = block_pfn;
}
/* Ensure the end of the pageblock or zone is online and valid */
block_pfn = pageblock_end_pfn(pfn) - 1;
block_pfn = min(block_pfn, zone_end_pfn(zone) - 1);
end_page = pfn_to_online_page(block_pfn);
if (!end_page)
return false;
/*
* Only clear the hint if a sample indicates there is either a
* free page or an LRU page in the block. One or other condition
* is necessary for the block to be a migration source/target.
*/
do {
if (pfn_valid_within(pfn)) {
if (check_source && PageLRU(page)) {
clear_pageblock_skip(page);
return true;
}
if (check_target && PageBuddy(page)) {
clear_pageblock_skip(page);
return true;
}
}
page += (1 << PAGE_ALLOC_COSTLY_ORDER);
pfn += (1 << PAGE_ALLOC_COSTLY_ORDER);
} while (page <= end_page);
return false;
}
/*
* This function is called to clear all cached information on pageblocks that
* should be skipped for page isolation when the migrate and free page scanner
* meet.
*/
static void __reset_isolation_suitable(struct zone *zone)
{
unsigned long migrate_pfn = zone->zone_start_pfn;
unsigned long free_pfn = zone_end_pfn(zone) - 1;
unsigned long reset_migrate = free_pfn;
unsigned long reset_free = migrate_pfn;
bool source_set = false;
bool free_set = false;
if (!zone->compact_blockskip_flush)
return;
zone->compact_blockskip_flush = false;
/*
* Walk the zone and update pageblock skip information. Source looks
* for PageLRU while target looks for PageBuddy. When the scanner
* is found, both PageBuddy and PageLRU are checked as the pageblock
* is suitable as both source and target.
*/
for (; migrate_pfn < free_pfn; migrate_pfn += pageblock_nr_pages,
free_pfn -= pageblock_nr_pages) {
cond_resched();
/* Update the migrate PFN */
if (__reset_isolation_pfn(zone, migrate_pfn, true, source_set) &&
migrate_pfn < reset_migrate) {
source_set = true;
reset_migrate = migrate_pfn;
zone->compact_init_migrate_pfn = reset_migrate;
zone->compact_cached_migrate_pfn[0] = reset_migrate;
zone->compact_cached_migrate_pfn[1] = reset_migrate;
}
/* Update the free PFN */
if (__reset_isolation_pfn(zone, free_pfn, free_set, true) &&
free_pfn > reset_free) {
free_set = true;
reset_free = free_pfn;
zone->compact_init_free_pfn = reset_free;
zone->compact_cached_free_pfn = reset_free;
}
}
/* Leave no distance if no suitable block was reset */
if (reset_migrate >= reset_free) {
zone->compact_cached_migrate_pfn[0] = migrate_pfn;
zone->compact_cached_migrate_pfn[1] = migrate_pfn;
zone->compact_cached_free_pfn = free_pfn;
}
}
void reset_isolation_suitable(pg_data_t *pgdat)
{
int zoneid;
for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
struct zone *zone = &pgdat->node_zones[zoneid];
if (!populated_zone(zone))
continue;
/* Only flush if a full compaction finished recently */
if (zone->compact_blockskip_flush)
__reset_isolation_suitable(zone);
}
}
/*
* Sets the pageblock skip bit if it was clear. Note that this is a hint as
* locks are not required for read/writers. Returns true if it was already set.
*/
static bool test_and_set_skip(struct compact_control *cc, struct page *page,
unsigned long pfn)
{
bool skip;
/* Do no update if skip hint is being ignored */
if (cc->ignore_skip_hint)
return false;
if (!IS_ALIGNED(pfn, pageblock_nr_pages))
return false;
skip = get_pageblock_skip(page);
if (!skip && !cc->no_set_skip_hint)
set_pageblock_skip(page);
return skip;
}
static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
{
struct zone *zone = cc->zone;
pfn = pageblock_end_pfn(pfn);
/* Set for isolation rather than compaction */
if (cc->no_set_skip_hint)
return;
if (pfn > zone->compact_cached_migrate_pfn[0])
zone->compact_cached_migrate_pfn[0] = pfn;
if (cc->mode != MIGRATE_ASYNC &&
pfn > zone->compact_cached_migrate_pfn[1])
zone->compact_cached_migrate_pfn[1] = pfn;
}
/*
* If no pages were isolated then mark this pageblock to be skipped in the
* future. The information is later cleared by __reset_isolation_suitable().
*/
static void update_pageblock_skip(struct compact_control *cc,
struct page *page, unsigned long pfn)
{
struct zone *zone = cc->zone;
if (cc->no_set_skip_hint)
return;
if (!page)
return;
set_pageblock_skip(page);
/* Update where async and sync compaction should restart */
if (pfn < zone->compact_cached_free_pfn)
zone->compact_cached_free_pfn = pfn;
}
#else
static inline bool isolation_suitable(struct compact_control *cc,
struct page *page)
{
return true;
}
static inline bool pageblock_skip_persistent(struct page *page)
{
return false;
}
static inline void update_pageblock_skip(struct compact_control *cc,
struct page *page, unsigned long pfn)
{
}
static void update_cached_migrate(struct compact_control *cc, unsigned long pfn)
{
}
static bool test_and_set_skip(struct compact_control *cc, struct page *page,
unsigned long pfn)
{
return false;
}
#endif /* CONFIG_COMPACTION */
/*
* Compaction requires the taking of some coarse locks that are potentially
* very heavily contended. For async compaction, trylock and record if the
* lock is contended. The lock will still be acquired but compaction will
* abort when the current block is finished regardless of success rate.
* Sync compaction acquires the lock.
*
* Always returns true which makes it easier to track lock state in callers.
*/
static bool compact_lock_irqsave(spinlock_t *lock, unsigned long *flags,
struct compact_control *cc)
__acquires(lock)
{
/* Track if the lock is contended in async mode */
if (cc->mode == MIGRATE_ASYNC && !cc->contended) {
if (spin_trylock_irqsave(lock, *flags))
return true;
cc->contended = true;
}
spin_lock_irqsave(lock, *flags);
return true;
}
/*
* Compaction requires the taking of some coarse locks that are potentially
* very heavily contended. The lock should be periodically unlocked to avoid
* having disabled IRQs for a long time, even when there is nobody waiting on
* the lock. It might also be that allowing the IRQs will result in
* need_resched() becoming true. If scheduling is needed, async compaction
* aborts. Sync compaction schedules.
* Either compaction type will also abort if a fatal signal is pending.
* In either case if the lock was locked, it is dropped and not regained.
*
* Returns true if compaction should abort due to fatal signal pending, or
* async compaction due to need_resched()
* Returns false when compaction can continue (sync compaction might have
* scheduled)
*/
static bool compact_unlock_should_abort(spinlock_t *lock,
unsigned long flags, bool *locked, struct compact_control *cc)
{
if (*locked) {
spin_unlock_irqrestore(lock, flags);
*locked = false;
}
if (fatal_signal_pending(current)) {
cc->contended = true;
return true;
}
cond_resched();
return false;
}
/*
* Isolate free pages onto a private freelist. If @strict is true, will abort
* returning 0 on any invalid PFNs or non-free pages inside of the pageblock
* (even though it may still end up isolating some pages).
*/
static unsigned long isolate_freepages_block(struct compact_control *cc,
unsigned long *start_pfn,
unsigned long end_pfn,
struct list_head *freelist,
unsigned int stride,
bool strict)
{
int nr_scanned = 0, total_isolated = 0;
struct page *cursor;
unsigned long flags = 0;
bool locked = false;
unsigned long blockpfn = *start_pfn;
unsigned int order;
/* Strict mode is for isolation, speed is secondary */
if (strict)
stride = 1;
cursor = pfn_to_page(blockpfn);
/* Isolate free pages. */
for (; blockpfn < end_pfn; blockpfn += stride, cursor += stride) {
int isolated;
struct page *page = cursor;
/*
* Periodically drop the lock (if held) regardless of its
* contention, to give chance to IRQs. Abort if fatal signal
* pending or async compaction detects need_resched()
*/
if (!(blockpfn % SWAP_CLUSTER_MAX)
&& compact_unlock_should_abort(&cc->zone->lock, flags,
&locked, cc))
break;
nr_scanned++;
if (!pfn_valid_within(blockpfn))
goto isolate_fail;
/*
* For compound pages such as THP and hugetlbfs, we can save
* potentially a lot of iterations if we skip them at once.
* The check is racy, but we can consider only valid values
* and the only danger is skipping too much.
*/
if (PageCompound(page)) {
const unsigned int order = compound_order(page);
if (likely(order < MAX_ORDER)) {
blockpfn += (1UL << order) - 1;
cursor += (1UL << order) - 1;
}
goto isolate_fail;
}
if (!PageBuddy(page))
goto isolate_fail;
/*
* If we already hold the lock, we can skip some rechecking.
* Note that if we hold the lock now, checked_pageblock was
* already set in some previous iteration (or strict is true),
* so it is correct to skip the suitable migration target
* recheck as well.
*/
if (!locked) {
locked = compact_lock_irqsave(&cc->zone->lock,
&flags, cc);
/* Recheck this is a buddy page under lock */
if (!PageBuddy(page))
goto isolate_fail;
}
/* Found a free page, will break it into order-0 pages */
order = buddy_order(page);
isolated = __isolate_free_page(page, order);
if (!isolated)
break;
set_page_private(page, order);
total_isolated += isolated;
cc->nr_freepages += isolated;
list_add_tail(&page->lru, freelist);
if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
blockpfn += isolated;
break;
}
/* Advance to the end of split page */
blockpfn += isolated - 1;
cursor += isolated - 1;
continue;
isolate_fail:
if (strict)
break;
else
continue;
}
if (locked)
spin_unlock_irqrestore(&cc->zone->lock, flags);
/*
* There is a tiny chance that we have read bogus compound_order(),
* so be careful to not go outside of the pageblock.
*/
if (unlikely(blockpfn > end_pfn))
blockpfn = end_pfn;
trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
nr_scanned, total_isolated);
/* Record how far we have got within the block */
*start_pfn = blockpfn;
/*
* If strict isolation is requested by CMA then check that all the
* pages requested were isolated. If there were any failures, 0 is
* returned and CMA will fail.
*/
if (strict && blockpfn < end_pfn)
total_isolated = 0;
cc->total_free_scanned += nr_scanned;
if (total_isolated)
count_compact_events(COMPACTISOLATED, total_isolated);
return total_isolated;
}
/**
* isolate_freepages_range() - isolate free pages.
* @cc: Compaction control structure.
* @start_pfn: The first PFN to start isolating.
* @end_pfn: The one-past-last PFN.
*
* Non-free pages, invalid PFNs, or zone boundaries within the
* [start_pfn, end_pfn) range are considered errors, cause function to
* undo its actions and return zero.
*
* Otherwise, function returns one-past-the-last PFN of isolated page
* (which may be greater then end_pfn if end fell in a middle of
* a free page).
*/
unsigned long
isolate_freepages_range(struct compact_control *cc,
unsigned long start_pfn, unsigned long end_pfn)
{
unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
LIST_HEAD(freelist);
pfn = start_pfn;
block_start_pfn = pageblock_start_pfn(pfn);
if (block_start_pfn < cc->zone->zone_start_pfn)
block_start_pfn = cc->zone->zone_start_pfn;
block_end_pfn = pageblock_end_pfn(pfn);
for (; pfn < end_pfn; pfn += isolated,
block_start_pfn = block_end_pfn,
block_end_pfn += pageblock_nr_pages) {
/* Protect pfn from changing by isolate_freepages_block */
unsigned long isolate_start_pfn = pfn;
block_end_pfn = min(block_end_pfn, end_pfn);
/*
* pfn could pass the block_end_pfn if isolated freepage
* is more than pageblock order. In this case, we adjust
* scanning range to right one.
*/
if (pfn >= block_end_pfn) {
block_start_pfn = pageblock_start_pfn(pfn);
block_end_pfn = pageblock_end_pfn(pfn);
block_end_pfn = min(block_end_pfn, end_pfn);
}
if (!pageblock_pfn_to_page(block_start_pfn,
block_end_pfn, cc->zone))
break;
isolated = isolate_freepages_block(cc, &isolate_start_pfn,
block_end_pfn, &freelist, 0, true);
/*
* In strict mode, isolate_freepages_block() returns 0 if
* there are any holes in the block (ie. invalid PFNs or
* non-free pages).
*/
if (!isolated)
break;
/*
* If we managed to isolate pages, it is always (1 << n) *
* pageblock_nr_pages for some non-negative n. (Max order
* page may span two pageblocks).
*/
}
/* __isolate_free_page() does not map the pages */
split_map_pages(&freelist);
if (pfn < end_pfn) {
/* Loop terminated early, cleanup. */
release_freepages(&freelist);
return 0;
}
/* We don't use freelists for anything. */
return pfn;
}
/* Similar to reclaim, but different enough that they don't share logic */
static bool too_many_isolated(pg_data_t *pgdat)
{
unsigned long active, inactive, isolated;
inactive = node_page_state(pgdat, NR_INACTIVE_FILE) +
node_page_state(pgdat, NR_INACTIVE_ANON);
active = node_page_state(pgdat, NR_ACTIVE_FILE) +
node_page_state(pgdat, NR_ACTIVE_ANON);
isolated = node_page_state(pgdat, NR_ISOLATED_FILE) +
node_page_state(pgdat, NR_ISOLATED_ANON);
return isolated > (inactive + active) / 2;
}
/**
* isolate_migratepages_block() - isolate all migrate-able pages within
* a single pageblock
* @cc: Compaction control structure.
* @low_pfn: The first PFN to isolate
* @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
* @isolate_mode: Isolation mode to be used.
*
* Isolate all pages that can be migrated from the range specified by
* [low_pfn, end_pfn). The range is expected to be within same pageblock.
* Returns zero if there is a fatal signal pending, otherwise PFN of the
* first page that was not scanned (which may be both less, equal to or more
* than end_pfn).
*
* The pages are isolated on cc->migratepages list (not required to be empty),
* and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
* is neither read nor updated.
*/
static unsigned long
isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
unsigned long end_pfn, isolate_mode_t isolate_mode)
{
pg_data_t *pgdat = cc->zone->zone_pgdat;
unsigned long nr_scanned = 0, nr_isolated = 0;
struct lruvec *lruvec;
unsigned long flags = 0;
struct lruvec *locked = NULL;
struct page *page = NULL, *valid_page = NULL;
unsigned long start_pfn = low_pfn;
bool skip_on_failure = false;
unsigned long next_skip_pfn = 0;
bool skip_updated = false;
/*
* Ensure that there are not too many pages isolated from the LRU
* list by either parallel reclaimers or compaction. If there are,
* delay for some time until fewer pages are isolated
*/
while (unlikely(too_many_isolated(pgdat))) {
/* stop isolation if there are still pages not migrated */
if (cc->nr_migratepages)
return 0;
/* async migration should just abort */
if (cc->mode == MIGRATE_ASYNC)
return 0;
congestion_wait(BLK_RW_ASYNC, HZ/10);
if (fatal_signal_pending(current))
return 0;
}
cond_resched();
if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
skip_on_failure = true;
next_skip_pfn = block_end_pfn(low_pfn, cc->order);
}
/* Time to isolate some pages for migration */
for (; low_pfn < end_pfn; low_pfn++) {
if (skip_on_failure && low_pfn >= next_skip_pfn) {
/*
* We have isolated all migration candidates in the
* previous order-aligned block, and did not skip it due
* to failure. We should migrate the pages now and
* hopefully succeed compaction.
*/
if (nr_isolated)
break;
/*
* We failed to isolate in the previous order-aligned
* block. Set the new boundary to the end of the
* current block. Note we can't simply increase
* next_skip_pfn by 1 << order, as low_pfn might have
* been incremented by a higher number due to skipping
* a compound or a high-order buddy page in the
* previous loop iteration.
*/
next_skip_pfn = block_end_pfn(low_pfn, cc->order);
}
/*
* Periodically drop the lock (if held) regardless of its
* contention, to give chance to IRQs. Abort completely if
* a fatal signal is pending.
*/
if (!(low_pfn % SWAP_CLUSTER_MAX)) {
if (locked) {
unlock_page_lruvec_irqrestore(locked, flags);
locked = NULL;
}
if (fatal_signal_pending(current)) {
cc->contended = true;
low_pfn = 0;
goto fatal_pending;
}
cond_resched();
}
if (!pfn_valid_within(low_pfn))
goto isolate_fail;
nr_scanned++;
page = pfn_to_page(low_pfn);
/*
* Check if the pageblock has already been marked skipped.
* Only the aligned PFN is checked as the caller isolates
* COMPACT_CLUSTER_MAX at a time so the second call must
* not falsely conclude that the block should be skipped.
*/
if (!valid_page && IS_ALIGNED(low_pfn, pageblock_nr_pages)) {
if (!cc->ignore_skip_hint && get_pageblock_skip(page)) {
low_pfn = end_pfn;
page = NULL;
goto isolate_abort;
}
valid_page = page;
}
/*
* Skip if free. We read page order here without zone lock
* which is generally unsafe, but the race window is small and
* the worst thing that can happen is that we skip some
* potential isolation targets.
*/
if (PageBuddy(page)) {
unsigned long freepage_order = buddy_order_unsafe(page);
/*
* Without lock, we cannot be sure that what we got is
* a valid page order. Consider only values in the
* valid order range to prevent low_pfn overflow.
*/
if (freepage_order > 0 && freepage_order < MAX_ORDER)
low_pfn += (1UL << freepage_order) - 1;
continue;
}
/*
* Regardless of being on LRU, compound pages such as THP and
* hugetlbfs are not to be compacted unless we are attempting
* an allocation much larger than the huge page size (eg CMA).
* We can potentially save a lot of iterations if we skip them
* at once. The check is racy, but we can consider only valid
* values and the only danger is skipping too much.
*/
if (PageCompound(page) && !cc->alloc_contig) {
const unsigned int order = compound_order(page);
if (likely(order < MAX_ORDER))
low_pfn += (1UL << order) - 1;
goto isolate_fail;
}
/*
* Check may be lockless but that's ok as we recheck later.
* It's possible to migrate LRU and non-lru movable pages.
* Skip any other type of page
*/
if (!PageLRU(page)) {
/*
* __PageMovable can return false positive so we need
* to verify it under page_lock.
*/
if (unlikely(__PageMovable(page)) &&
!PageIsolated(page)) {
if (locked) {
unlock_page_lruvec_irqrestore(locked, flags);
locked = NULL;
}
if (!isolate_movable_page(page, isolate_mode))
goto isolate_success;
}
goto isolate_fail;
}
/*
* Migration will fail if an anonymous page is pinned in memory,
* so avoid taking lru_lock and isolating it unnecessarily in an
* admittedly racy check.
*/
if (!page_mapping(page) &&
page_count(page) > page_mapcount(page))
goto isolate_fail;
/*
* Only allow to migrate anonymous pages in GFP_NOFS context
* because those do not depend on fs locks.
*/
if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
goto isolate_fail;
/*
* Be careful not to clear PageLRU until after we're
* sure the page is not being freed elsewhere -- the
* page release code relies on it.
*/
if (unlikely(!get_page_unless_zero(page)))
goto isolate_fail;
if (!__isolate_lru_page_prepare(page, isolate_mode))
goto isolate_fail_put;
/* Try isolate the page */
if (!TestClearPageLRU(page))
goto isolate_fail_put;
lruvec = mem_cgroup_page_lruvec(page, pgdat);
/* If we already hold the lock, we can skip some rechecking */
if (lruvec != locked) {
if (locked)
unlock_page_lruvec_irqrestore(locked, flags);
compact_lock_irqsave(&lruvec->lru_lock, &flags, cc);
locked = lruvec;
lruvec_memcg_debug(lruvec, page);
/* Try get exclusive access under lock */
if (!skip_updated) {
skip_updated = true;
if (test_and_set_skip(cc, page, low_pfn))
goto isolate_abort;
}
/*
* Page become compound since the non-locked check,
* and it's on LRU. It can only be a THP so the order
* is safe to read and it's 0 for tail pages.
*/
if (unlikely(PageCompound(page) && !cc->alloc_contig)) {
low_pfn += compound_nr(page) - 1;
SetPageLRU(page);
goto isolate_fail_put;
}
}
/* The whole page is taken off the LRU; skip the tail pages. */
if (PageCompound(page))
low_pfn += compound_nr(page) - 1;
/* Successfully isolated */
del_page_from_lru_list(page, lruvec);
mod_node_page_state(page_pgdat(page),
NR_ISOLATED_ANON + page_is_file_lru(page),
thp_nr_pages(page));
isolate_success:
list_add(&page->lru, &cc->migratepages);
cc->nr_migratepages += compound_nr(page);
nr_isolated += compound_nr(page);
/*
* Avoid isolating too much unless this block is being
* rescanned (e.g. dirty/writeback pages, parallel allocation)
* or a lock is contended. For contention, isolate quickly to
* potentially remove one source of contention.
*/
if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX &&
!cc->rescan && !cc->contended) {
++low_pfn;
break;
}
continue;
isolate_fail_put:
/* Avoid potential deadlock in freeing page under lru_lock */
if (locked) {
unlock_page_lruvec_irqrestore(locked, flags);
locked = NULL;
}
put_page(page);
isolate_fail:
if (!skip_on_failure)
continue;
/*
* We have isolated some pages, but then failed. Release them
* instead of migrating, as we cannot form the cc->order buddy
* page anyway.
*/
if (nr_isolated) {
if (locked) {
unlock_page_lruvec_irqrestore(locked, flags);
locked = NULL;
}
putback_movable_pages(&cc->migratepages);
cc->nr_migratepages = 0;
nr_isolated = 0;
}
if (low_pfn < next_skip_pfn) {
low_pfn = next_skip_pfn - 1;
/*
* The check near the loop beginning would have updated
* next_skip_pfn too, but this is a bit simpler.
*/
next_skip_pfn += 1UL << cc->order;
}
}
/*
* The PageBuddy() check could have potentially brought us outside
* the range to be scanned.
*/
if (unlikely(low_pfn > end_pfn))
low_pfn = end_pfn;
page = NULL;
isolate_abort:
if (locked)
unlock_page_lruvec_irqrestore(locked, flags);
if (page) {
SetPageLRU(page);
put_page(page);
}
/*
* Updated the cached scanner pfn once the pageblock has been scanned
* Pages will either be migrated in which case there is no point
* scanning in the near future or migration failed in which case the
* failure reason may persist. The block is marked for skipping if
* there were no pages isolated in the block or if the block is
* rescanned twice in a row.
*/
if (low_pfn == end_pfn && (!nr_isolated || cc->rescan)) {
if (valid_page && !skip_updated)
set_pageblock_skip(valid_page);
update_cached_migrate(cc, low_pfn);
}
trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
nr_scanned, nr_isolated);
fatal_pending:
cc->total_migrate_scanned += nr_scanned;
if (nr_isolated)
count_compact_events(COMPACTISOLATED, nr_isolated);
return low_pfn;
}
/**
* isolate_migratepages_range() - isolate migrate-able pages in a PFN range
* @cc: Compaction control structure.
* @start_pfn: The first PFN to start isolating.
* @end_pfn: The one-past-last PFN.
*
* Returns zero if isolation fails fatally due to e.g. pending signal.
* Otherwise, function returns one-past-the-last PFN of isolated page
* (which may be greater than end_pfn if end fell in a middle of a THP page).
*/
unsigned long
isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
unsigned long end_pfn)
{
unsigned long pfn, block_start_pfn, block_end_pfn;
/* Scan block by block. First and last block may be incomplete */
pfn = start_pfn;
block_start_pfn = pageblock_start_pfn(pfn);
if (block_start_pfn < cc->zone->zone_start_pfn)
block_start_pfn = cc->zone->zone_start_pfn;
block_end_pfn = pageblock_end_pfn(pfn);
for (; pfn < end_pfn; pfn = block_end_pfn,
block_start_pfn = block_end_pfn,
block_end_pfn += pageblock_nr_pages) {
block_end_pfn = min(block_end_pfn, end_pfn);
if (!pageblock_pfn_to_page(block_start_pfn,
block_end_pfn, cc->zone))
continue;
pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
ISOLATE_UNEVICTABLE);
if (!pfn)
break;
if (cc->nr_migratepages >= COMPACT_CLUSTER_MAX)
break;
}
return pfn;
}
#endif /* CONFIG_COMPACTION || CONFIG_CMA */
#ifdef CONFIG_COMPACTION
static bool suitable_migration_source(struct compact_control *cc,
struct page *page)
{
int block_mt;
if (pageblock_skip_persistent(page))
return false;
if ((cc->mode != MIGRATE_ASYNC) || !cc->direct_compaction)
return true;
block_mt = get_pageblock_migratetype(page);
if (cc->migratetype == MIGRATE_MOVABLE)
return is_migrate_movable(block_mt);
else
return block_mt == cc->migratetype;
}
/* Returns true if the page is within a block suitable for migration to */
static bool suitable_migration_target(struct compact_control *cc,
struct page *page)
{
/* If the page is a large free page, then disallow migration */
if (PageBuddy(page)) {
/*
* We are checking page_order without zone->lock taken. But
* the only small danger is that we skip a potentially suitable
* pageblock, so it's not worth to check order for valid range.
*/
if (buddy_order_unsafe(page) >= pageblock_order)
return false;
}
if (cc->ignore_block_suitable)
return true;
/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
if (is_migrate_movable(get_pageblock_migratetype(page)))
return true;
/* Otherwise skip the block */
return false;
}
static inline unsigned int
freelist_scan_limit(struct compact_control *cc)
{
unsigned short shift = BITS_PER_LONG - 1;
return (COMPACT_CLUSTER_MAX >> min(shift, cc->fast_search_fail)) + 1;
}
/*
* Test whether the free scanner has reached the same or lower pageblock than
* the migration scanner, and compaction should thus terminate.
*/
static inline bool compact_scanners_met(struct compact_control *cc)
{
return (cc->free_pfn >> pageblock_order)
<= (cc->migrate_pfn >> pageblock_order);
}
/*
* Used when scanning for a suitable migration target which scans freelists
* in reverse. Reorders the list such as the unscanned pages are scanned
* first on the next iteration of the free scanner
*/
static void
move_freelist_head(struct list_head *freelist, struct page *freepage)
{
LIST_HEAD(sublist);
if (!list_is_last(freelist, &freepage->lru)) {
list_cut_before(&sublist, freelist, &freepage->lru);
if (!list_empty(&sublist))
list_splice_tail(&sublist, freelist);
}
}
/*
* Similar to move_freelist_head except used by the migration scanner
* when scanning forward. It's possible for these list operations to
* move against each other if they search the free list exactly in
* lockstep.
*/
static void
move_freelist_tail(struct list_head *freelist, struct page *freepage)
{
LIST_HEAD(sublist);
if (!list_is_first(freelist, &freepage->lru)) {
list_cut_position(&sublist, freelist, &freepage->lru);
if (!list_empty(&sublist))
list_splice_tail(&sublist, freelist);
}
}
static void
fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long nr_isolated)
{
unsigned long start_pfn, end_pfn;
struct page *page;
/* Do not search around if there are enough pages already */
if (cc->nr_freepages >= cc->nr_migratepages)
return;
/* Minimise scanning during async compaction */
if (cc->direct_compaction && cc->mode == MIGRATE_ASYNC)
return;
/* Pageblock boundaries */
start_pfn = max(pageblock_start_pfn(pfn), cc->zone->zone_start_pfn);
end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone));
page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone);
if (!page)
return;
/* Scan before */
if (start_pfn != pfn) {
isolate_freepages_block(cc, &start_pfn, pfn, &cc->freepages, 1, false);
if (cc->nr_freepages >= cc->nr_migratepages)
return;
}
/* Scan after */
start_pfn = pfn + nr_isolated;
if (start_pfn < end_pfn)
isolate_freepages_block(cc, &start_pfn, end_pfn, &cc->freepages, 1, false);
/* Skip this pageblock in the future as it's full or nearly full */
if (cc->nr_freepages < cc->nr_migratepages)
set_pageblock_skip(page);
}
/* Search orders in round-robin fashion */
static int next_search_order(struct compact_control *cc, int order)
{
order--;
if (order < 0)
order = cc->order - 1;
/* Search wrapped around? */
if (order == cc->search_order) {
cc->search_order--;
if (cc->search_order < 0)
cc->search_order = cc->order - 1;
return -1;
}
return order;
}
static unsigned long
fast_isolate_freepages(struct compact_control *cc)
{
unsigned int limit = min(1U, freelist_scan_limit(cc) >> 1);
unsigned int nr_scanned = 0;
unsigned long low_pfn, min_pfn, highest = 0;
unsigned long nr_isolated = 0;
unsigned long distance;
struct page *page = NULL;
bool scan_start = false;
int order;
/* Full compaction passes in a negative order */
if (cc->order <= 0)
return cc->free_pfn;
/*
* If starting the scan, use a deeper search and use the highest
* PFN found if a suitable one is not found.
*/
if (cc->free_pfn >= cc->zone->compact_init_free_pfn) {
limit = pageblock_nr_pages >> 1;
scan_start = true;
}
/*
* Preferred point is in the top quarter of the scan space but take
* a pfn from the top half if the search is problematic.
*/
distance = (cc->free_pfn - cc->migrate_pfn);
low_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 2));
min_pfn = pageblock_start_pfn(cc->free_pfn - (distance >> 1));
if (WARN_ON_ONCE(min_pfn > low_pfn))
low_pfn = min_pfn;
/*
* Search starts from the last successful isolation order or the next
* order to search after a previous failure
*/
cc->search_order = min_t(unsigned int, cc->order - 1, cc->search_order);
for (order = cc->search_order;
!page && order >= 0;
order = next_search_order(cc, order)) {
struct free_area *area = &cc->zone->free_area[order];
struct list_head *freelist;
struct page *freepage;
unsigned long flags;
unsigned int order_scanned = 0;
unsigned long high_pfn = 0;
if (!area->nr_free)
continue;
spin_lock_irqsave(&cc->zone->lock, flags);
freelist = &area->free_list[MIGRATE_MOVABLE];
list_for_each_entry_reverse(freepage, freelist, lru) {
unsigned long pfn;
order_scanned++;
nr_scanned++;
pfn = page_to_pfn(freepage);
if (pfn >= highest)
highest = max(pageblock_start_pfn(pfn),
cc->zone->zone_start_pfn);
if (pfn >= low_pfn) {
cc->fast_search_fail = 0;
cc->search_order = order;
page = freepage;
break;
}
if (pfn >= min_pfn && pfn > high_pfn) {
high_pfn = pfn;
/* Shorten the scan if a candidate is found */
limit >>= 1;
}
if (order_scanned >= limit)
break;
}
/* Use a minimum pfn if a preferred one was not found */
if (!page && high_pfn) {
page = pfn_to_page(high_pfn);
/* Update freepage for the list reorder below */
freepage = page;
}
/* Reorder to so a future search skips recent pages */
move_freelist_head(freelist, freepage);
/* Isolate the page if available */
if (page) {
if (__isolate_free_page(page, order)) {
set_page_private(page, order);
nr_isolated = 1 << order;
cc->nr_freepages += nr_isolated;
list_add_tail(&page->lru, &cc->freepages);
count_compact_events(COMPACTISOLATED, nr_isolated);
} else {
/* If isolation fails, abort the search */
order = cc->search_order + 1;
page = NULL;
}
}
spin_unlock_irqrestore(&cc->zone->lock, flags);
/*
* Smaller scan on next order so the total scan ig related
* to freelist_scan_limit.
*/
if (order_scanned >= limit)
limit = min(1U, limit >> 1);
}
if (!page) {
cc->fast_search_fail++;
if (scan_start) {
/*
* Use the highest PFN found above min. If one was
* not found, be pessimistic for direct compaction
* and use the min mark.
*/
if (highest) {
page = pfn_to_page(highest);
cc->free_pfn = highest;
} else {
if (cc->direct_compaction && pfn_valid(min_pfn)) {
page = pageblock_pfn_to_page(min_pfn,
min(pageblock_end_pfn(min_pfn),
zone_end_pfn(cc->zone)),
cc->zone);
cc->free_pfn = min_pfn;
}
}
}
}
if (highest && highest >= cc->zone->compact_cached_free_pfn) {
highest -= pageblock_nr_pages;
cc->zone->compact_cached_free_pfn = highest;
}
cc->total_free_scanned += nr_scanned;
if (!page)
return cc->free_pfn;
low_pfn = page_to_pfn(page);
fast_isolate_around(cc, low_pfn, nr_isolated);
return low_pfn;
}
/*
* Based on information in the current compact_control, find blocks
* suitable for isolating free pages from and then isolate them.
*/
static void isolate_freepages(struct compact_control *cc)
{
struct zone *zone = cc->zone;
struct page *page;
unsigned long block_start_pfn; /* start of current pageblock */
unsigned long isolate_start_pfn; /* exact pfn we start at */
unsigned long block_end_pfn; /* end of current pageblock */
unsigned long low_pfn; /* lowest pfn scanner is able to scan */
struct list_head *freelist = &cc->freepages;
unsigned int stride;
/* Try a small search of the free lists for a candidate */
isolate_start_pfn = fast_isolate_freepages(cc);
if (cc->nr_freepages)
goto splitmap;
/*
* Initialise the free scanner. The starting point is where we last
* successfully isolated from, zone-cached value, or the end of the
* zone when isolating for the first time. For looping we also need
* this pfn aligned down to the pageblock boundary, because we do
* block_start_pfn -= pageblock_nr_pages in the for loop.
* For ending point, take care when isolating in last pageblock of a
* zone which ends in the middle of a pageblock.
* The low boundary is the end of the pageblock the migration scanner
* is using.
*/
isolate_start_pfn = cc->free_pfn;
block_start_pfn = pageblock_start_pfn(isolate_start_pfn);
block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
zone_end_pfn(zone));
low_pfn = pageblock_end_pfn(cc->migrate_pfn);
stride = cc->mode == MIGRATE_ASYNC ? COMPACT_CLUSTER_MAX : 1;
/*
* Isolate free pages until enough are available to migrate the
* pages on cc->migratepages. We stop searching if the migrate
* and free page scanners meet or enough free pages are isolated.
*/
for (; block_start_pfn >= low_pfn;
block_end_pfn = block_start_pfn,
block_start_pfn -= pageblock_nr_pages,
isolate_start_pfn = block_start_pfn) {
unsigned long nr_isolated;
/*
* This can iterate a massively long zone without finding any
* suitable migration targets, so periodically check resched.
*/
if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
cond_resched();
page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
zone);
if (!page)
continue;
/* Check the block is suitable for migration */
if (!suitable_migration_target(cc, page))
continue;
/* If isolation recently failed, do not retry */
if (!isolation_suitable(cc, page))
continue;
/* Found a block suitable for isolating free pages from. */
nr_isolated = isolate_freepages_block(cc, &isolate_start_pfn,
block_end_pfn, freelist, stride, false);
/* Update the skip hint if the full pageblock was scanned */
if (isolate_start_pfn == block_end_pfn)
update_pageblock_skip(cc, page, block_start_pfn);
/* Are enough freepages isolated? */
if (cc->nr_freepages >= cc->nr_migratepages) {
if (isolate_start_pfn >= block_end_pfn) {
/*
* Restart at previous pageblock if more
* freepages can be isolated next time.
*/
isolate_start_pfn =
block_start_pfn - pageblock_nr_pages;
}
break;
} else if (isolate_start_pfn < block_end_pfn) {
/*
* If isolation failed early, do not continue
* needlessly.
*/
break;
}
/* Adjust stride depending on isolation */
if (nr_isolated) {
stride = 1;
continue;
}
stride = min_t(unsigned int, COMPACT_CLUSTER_MAX, stride << 1);
}
/*
* Record where the free scanner will restart next time. Either we
* broke from the loop and set isolate_start_pfn based on the last
* call to isolate_freepages_block(), or we met the migration scanner
* and the loop terminated due to isolate_start_pfn < low_pfn
*/
cc->free_pfn = isolate_start_pfn;
splitmap:
/* __isolate_free_page() does not map the pages */
split_map_pages(freelist);
}
/*
* This is a migrate-callback that "allocates" freepages by taking pages
* from the isolated freelists in the block we are migrating to.
*/
static struct page *compaction_alloc(struct page *migratepage,
unsigned long data)
{
struct compact_control *cc = (struct compact_control *)data;
struct page *freepage;
if (list_empty(&cc->freepages)) {
isolate_freepages(cc);
if (list_empty(&cc->freepages))
return NULL;
}
freepage = list_entry(cc->freepages.next, struct page, lru);
list_del(&freepage->lru);
cc->nr_freepages--;
return freepage;
}
/*
* This is a migrate-callback that "frees" freepages back to the isolated
* freelist. All pages on the freelist are from the same zone, so there is no
* special handling needed for NUMA.
*/
static void compaction_free(struct page *page, unsigned long data)
{
struct compact_control *cc = (struct compact_control *)data;
list_add(&page->lru, &cc->freepages);
cc->nr_freepages++;
}
/* possible outcome of isolate_migratepages */
typedef enum {
ISOLATE_ABORT, /* Abort compaction now */
ISOLATE_NONE, /* No pages isolated, continue scanning */
ISOLATE_SUCCESS, /* Pages isolated, migrate */
} isolate_migrate_t;
/*
* Allow userspace to control policy on scanning the unevictable LRU for
* compactable pages.
*/
#ifdef CONFIG_PREEMPT_RT
int sysctl_compact_unevictable_allowed __read_mostly = 0;
#else
int sysctl_compact_unevictable_allowed __read_mostly = 1;
#endif
static inline void
update_fast_start_pfn(struct compact_control *cc, unsigned long pfn)
{
if (cc->fast_start_pfn == ULONG_MAX)
return;
if (!cc->fast_start_pfn)
cc->fast_start_pfn = pfn;
cc->fast_start_pfn = min(cc->fast_start_pfn, pfn);
}
static inline unsigned long
reinit_migrate_pfn(struct compact_control *cc)
{
if (!cc->fast_start_pfn || cc->fast_start_pfn == ULONG_MAX)
return cc->migrate_pfn;
cc->migrate_pfn = cc->fast_start_pfn;
cc->fast_start_pfn = ULONG_MAX;
return cc->migrate_pfn;
}
/*
* Briefly search the free lists for a migration source that already has
* some free pages to reduce the number of pages that need migration
* before a pageblock is free.
*/
static unsigned long fast_find_migrateblock(struct compact_control *cc)
{
unsigned int limit = freelist_scan_limit(cc);
unsigned int nr_scanned = 0;
unsigned long distance;
unsigned long pfn = cc->migrate_pfn;
unsigned long high_pfn;
int order;
bool found_block = false;
/* Skip hints are relied on to avoid repeats on the fast search */
if (cc->ignore_skip_hint)
return pfn;
/*
* If the migrate_pfn is not at the start of a zone or the start
* of a pageblock then assume this is a continuation of a previous
* scan restarted due to COMPACT_CLUSTER_MAX.
*/
if (pfn != cc->zone->zone_start_pfn && pfn != pageblock_start_pfn(pfn))
return pfn;
/*
* For smaller orders, just linearly scan as the number of pages
* to migrate should be relatively small and does not necessarily
* justify freeing up a large block for a small allocation.
*/
if (cc->order <= PAGE_ALLOC_COSTLY_ORDER)
return pfn;
/*
* Only allow kcompactd and direct requests for movable pages to
* quickly clear out a MOVABLE pageblock for allocation. This
* reduces the risk that a large movable pageblock is freed for
* an unmovable/reclaimable small allocation.
*/
if (cc->direct_compaction && cc->migratetype != MIGRATE_MOVABLE)
return pfn;
/*
* When starting the migration scanner, pick any pageblock within the
* first half of the search space. Otherwise try and pick a pageblock
* within the first eighth to reduce the chances that a migration
* target later becomes a source.
*/
distance = (cc->free_pfn - cc->migrate_pfn) >> 1;
if (cc->migrate_pfn != cc->zone->zone_start_pfn)
distance >>= 2;
high_pfn = pageblock_start_pfn(cc->migrate_pfn + distance);
for (order = cc->order - 1;
order >= PAGE_ALLOC_COSTLY_ORDER && !found_block && nr_scanned < limit;
order--) {
struct free_area *area = &cc->zone->free_area[order];
struct list_head *freelist;
unsigned long flags;
struct page *freepage;
if (!area->nr_free)
continue;
spin_lock_irqsave(&cc->zone->lock, flags);
freelist = &area->free_list[MIGRATE_MOVABLE];
list_for_each_entry(freepage, freelist, lru) {
unsigned long free_pfn;
if (nr_scanned++ >= limit) {
move_freelist_tail(freelist, freepage);
break;
}
free_pfn = page_to_pfn(freepage);
if (free_pfn < high_pfn) {
/*
* Avoid if skipped recently. Ideally it would
* move to the tail but even safe iteration of
* the list assumes an entry is deleted, not
* reordered.
*/
if (get_pageblock_skip(freepage))
continue;
/* Reorder to so a future search skips recent pages */
move_freelist_tail(freelist, freepage);
update_fast_start_pfn(cc, free_pfn);
pfn = pageblock_start_pfn(free_pfn);
cc->fast_search_fail = 0;
found_block = true;
set_pageblock_skip(freepage);
break;
}
}
spin_unlock_irqrestore(&cc->zone->lock, flags);
}
cc->total_migrate_scanned += nr_scanned;
/*
* If fast scanning failed then use a cached entry for a page block
* that had free pages as the basis for starting a linear scan.
*/
if (!found_block) {
cc->fast_search_fail++;
pfn = reinit_migrate_pfn(cc);
}
return pfn;
}
/*
* Isolate all pages that can be migrated from the first suitable block,
* starting at the block pointed to by the migrate scanner pfn within
* compact_control.
*/
static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
{
unsigned long block_start_pfn;
unsigned long block_end_pfn;
unsigned long low_pfn;
struct page *page;
const isolate_mode_t isolate_mode =
(sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
(cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
bool fast_find_block;
/*
* Start at where we last stopped, or beginning of the zone as
* initialized by compact_zone(). The first failure will use
* the lowest PFN as the starting point for linear scanning.
*/
low_pfn = fast_find_migrateblock(cc);
block_start_pfn = pageblock_start_pfn(low_pfn);
if (block_start_pfn < cc->zone->zone_start_pfn)
block_start_pfn = cc->zone->zone_start_pfn;
/*
* fast_find_migrateblock marks a pageblock skipped so to avoid
* the isolation_suitable check below, check whether the fast
* search was successful.
*/
fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;
/* Only scan within a pageblock boundary */
block_end_pfn = pageblock_end_pfn(low_pfn);
/*
* Iterate over whole pageblocks until we find the first suitable.
* Do not cross the free scanner.
*/
for (; block_end_pfn <= cc->free_pfn;
fast_find_block = false,
low_pfn = block_end_pfn,
block_start_pfn = block_end_pfn,
block_end_pfn += pageblock_nr_pages) {
/*
* This can potentially iterate a massively long zone with
* many pageblocks unsuitable, so periodically check if we
* need to schedule.
*/
if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages)))
cond_resched();
page = pageblock_pfn_to_page(block_start_pfn,
block_end_pfn, cc->zone);
if (!page)
continue;
/*
* If isolation recently failed, do not retry. Only check the
* pageblock once. COMPACT_CLUSTER_MAX causes a pageblock
* to be visited multiple times. Assume skip was checked
* before making it "skip" so other compaction instances do
* not scan the same block.
*/
if (IS_ALIGNED(low_pfn, pageblock_nr_pages) &&
!fast_find_block && !isolation_suitable(cc, page))
continue;
/*
* For async compaction, also only scan in MOVABLE blocks
* without huge pages. Async compaction is optimistic to see
* if the minimum amount of work satisfies the allocation.
* The cached PFN is updated as it's possible that all
* remaining blocks between source and target are unsuitable
* and the compaction scanners fail to meet.
*/
if (!suitable_migration_source(cc, page)) {
update_cached_migrate(cc, block_end_pfn);
continue;
}
/* Perform the isolation */
low_pfn = isolate_migratepages_block(cc, low_pfn,
block_end_pfn, isolate_mode);
if (!low_pfn)
return ISOLATE_ABORT;
/*
* Either we isolated something and proceed with migration. Or
* we failed and compact_zone should decide if we should
* continue or not.
*/
break;
}
/* Record where migration scanner will be restarted. */
cc->migrate_pfn = low_pfn;
return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
}
/*
* order == -1 is expected when compacting via
* /proc/sys/vm/compact_memory
*/
static inline bool is_via_compact_memory(int order)
{
return order == -1;
}
static bool kswapd_is_running(pg_data_t *pgdat)
{
return pgdat->kswapd && (pgdat->kswapd->state == TASK_RUNNING);
}
/*
* A zone's fragmentation score is the external fragmentation wrt to the
* COMPACTION_HPAGE_ORDER. It returns a value in the range [0, 100].
*/
static unsigned int fragmentation_score_zone(struct zone *zone)
{
return extfrag_for_order(zone, COMPACTION_HPAGE_ORDER);
}
/*
* A weighted zone's fragmentation score is the external fragmentation
* wrt to the COMPACTION_HPAGE_ORDER scaled by the zone's size. It
* returns a value in the range [0, 100].
*
* The scaling factor ensures that proactive compaction focuses on larger
* zones like ZONE_NORMAL, rather than smaller, specialized zones like
* ZONE_DMA32. For smaller zones, the score value remains close to zero,
* and thus never exceeds the high threshold for proactive compaction.
*/
static unsigned int fragmentation_score_zone_weighted(struct zone *zone)
{
unsigned long score;
score = zone->present_pages * fragmentation_score_zone(zone);
return div64_ul(score, zone->zone_pgdat->node_present_pages + 1);
}
/*
* The per-node proactive (background) compaction process is started by its
* corresponding kcompactd thread when the node's fragmentation score
* exceeds the high threshold. The compaction process remains active till
* the node's score falls below the low threshold, or one of the back-off
* conditions is met.
*/
static unsigned int fragmentation_score_node(pg_data_t *pgdat)
{
unsigned int score = 0;
int zoneid;
for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
struct zone *zone;
zone = &pgdat->node_zones[zoneid];
score += fragmentation_score_zone_weighted(zone);
}
return score;
}
static unsigned int fragmentation_score_wmark(pg_data_t *pgdat, bool low)
{
unsigned int wmark_low;
/*
* Cap the low watermak to avoid excessive compaction
* activity in case a user sets the proactivess tunable
* close to 100 (maximum).
*/
wmark_low = max(100U - sysctl_compaction_proactiveness, 5U);
return low ? wmark_low : min(wmark_low + 10, 100U);
}
static bool should_proactive_compact_node(pg_data_t *pgdat)
{
int wmark_high;
if (!sysctl_compaction_proactiveness || kswapd_is_running(pgdat))
return false;
wmark_high = fragmentation_score_wmark(pgdat, false);
return fragmentation_score_node(pgdat) > wmark_high;
}
static enum compact_result __compact_finished(struct compact_control *cc)
{
unsigned int order;
const int migratetype = cc->migratetype;
int ret;
/* Compaction run completes if the migrate and free scanner meet */
if (compact_scanners_met(cc)) {
/* Let the next compaction start anew. */
reset_cached_positions(cc->zone);
/*
* Mark that the PG_migrate_skip information should be cleared
* by kswapd when it goes to sleep. kcompactd does not set the
* flag itself as the decision to be clear should be directly
* based on an allocation request.
*/
if (cc->direct_compaction)
cc->zone->compact_blockskip_flush = true;
if (cc->whole_zone)
return COMPACT_COMPLETE;
else
return COMPACT_PARTIAL_SKIPPED;
}
if (cc->proactive_compaction) {
int score, wmark_low;
pg_data_t *pgdat;
pgdat = cc->zone->zone_pgdat;
if (kswapd_is_running(pgdat))
return COMPACT_PARTIAL_SKIPPED;
score = fragmentation_score_zone(cc->zone);
wmark_low = fragmentation_score_wmark(pgdat, true);
if (score > wmark_low)
ret = COMPACT_CONTINUE;
else
ret = COMPACT_SUCCESS;
goto out;
}
if (is_via_compact_memory(cc->order))
return COMPACT_CONTINUE;
/*
* Always finish scanning a pageblock to reduce the possibility of
* fallbacks in the future. This is particularly important when
* migration source is unmovable/reclaimable but it's not worth
* special casing.
*/
if (!IS_ALIGNED(cc->migrate_pfn, pageblock_nr_pages))
return COMPACT_CONTINUE;
/* Direct compactor: Is a suitable page free? */
ret = COMPACT_NO_SUITABLE_PAGE;
for (order = cc->order; order < MAX_ORDER; order++) {
struct free_area *area = &cc->zone->free_area[order];
bool can_steal;
/* Job done if page is free of the right migratetype */
if (!free_area_empty(area, migratetype))
return COMPACT_SUCCESS;
#ifdef CONFIG_CMA
/* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
if (migratetype == MIGRATE_MOVABLE &&
!free_area_empty(area, MIGRATE_CMA))
return COMPACT_SUCCESS;
#endif
/*
* Job done if allocation would steal freepages from
* other migratetype buddy lists.
*/
if (find_suitable_fallback(area, order, migratetype,
true, &can_steal) != -1) {
/* movable pages are OK in any pageblock */
if (migratetype == MIGRATE_MOVABLE)
return COMPACT_SUCCESS;
/*
* We are stealing for a non-movable allocation. Make
* sure we finish compacting the current pageblock
* first so it is as free as possible and we won't
* have to steal another one soon. This only applies
* to sync compaction, as async compaction operates
* on pageblocks of the same migratetype.
*/
if (cc->mode == MIGRATE_ASYNC ||
IS_ALIGNED(cc->migrate_pfn,
pageblock_nr_pages)) {
return COMPACT_SUCCESS;
}
ret = COMPACT_CONTINUE;
break;
}
}
out:
if (cc->contended || fatal_signal_pending(current))
ret = COMPACT_CONTENDED;
return ret;
}
static enum compact_result compact_finished(struct compact_control *cc)
{
int ret;
ret = __compact_finished(cc);
trace_mm_compaction_finished(cc->zone, cc->order, ret);
if (ret == COMPACT_NO_SUITABLE_PAGE)
ret = COMPACT_CONTINUE;
return ret;
}
static enum compact_result __compaction_suitable(struct zone *zone, int order,
unsigned int alloc_flags,
int highest_zoneidx,
unsigned long wmark_target)
{
unsigned long watermark;
if (is_via_compact_memory(order))
return COMPACT_CONTINUE;
watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
/*
* If watermarks for high-order allocation are already met, there
* should be no need for compaction at all.
*/
if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
alloc_flags))
return COMPACT_SUCCESS;
/*
* Watermarks for order-0 must be met for compaction to be able to
* isolate free pages for migration targets. This means that the
* watermark and alloc_flags have to match, or be more pessimistic than
* the check in __isolate_free_page(). We don't use the direct
* compactor's alloc_flags, as they are not relevant for freepage
* isolation. We however do use the direct compactor's highest_zoneidx
* to skip over zones where lowmem reserves would prevent allocation
* even if compaction succeeds.
* For costly orders, we require low watermark instead of min for
* compaction to proceed to increase its chances.
* ALLOC_CMA is used, as pages in CMA pageblocks are considered
* suitable migration targets
*/
watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
low_wmark_pages(zone) : min_wmark_pages(zone);
watermark += compact_gap(order);
if (!__zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
ALLOC_CMA, wmark_target))
return COMPACT_SKIPPED;
return COMPACT_CONTINUE;
}
/*
* compaction_suitable: Is this suitable to run compaction on this zone now?
* Returns
* COMPACT_SKIPPED - If there are too few free pages for compaction
* COMPACT_SUCCESS - If the allocation would succeed without compaction
* COMPACT_CONTINUE - If compaction should run now
*/
enum compact_result compaction_suitable(struct zone *zone, int order,
unsigned int alloc_flags,
int highest_zoneidx)
{
enum compact_result ret;
int fragindex;
ret = __compaction_suitable(zone, order, alloc_flags, highest_zoneidx,
zone_page_state(zone, NR_FREE_PAGES));
/*
* fragmentation index determines if allocation failures are due to
* low memory or external fragmentation
*
* index of -1000 would imply allocations might succeed depending on
* watermarks, but we already failed the high-order watermark check
* index towards 0 implies failure is due to lack of memory
* index towards 1000 implies failure is due to fragmentation
*
* Only compact if a failure would be due to fragmentation. Also
* ignore fragindex for non-costly orders where the alternative to
* a successful reclaim/compaction is OOM. Fragindex and the
* vm.extfrag_threshold sysctl is meant as a heuristic to prevent
* excessive compaction for costly orders, but it should not be at the
* expense of system stability.
*/
if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
fragindex = fragmentation_index(zone, order);
if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
ret = COMPACT_NOT_SUITABLE_ZONE;
}
trace_mm_compaction_suitable(zone, order, ret);
if (ret == COMPACT_NOT_SUITABLE_ZONE)
ret = COMPACT_SKIPPED;
return ret;
}
bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
int alloc_flags)
{
struct zone *zone;
struct zoneref *z;
/*
* Make sure at least one zone would pass __compaction_suitable if we continue
* retrying the reclaim.
*/
for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
ac->highest_zoneidx, ac->nodemask) {
unsigned long available;
enum compact_result compact_result;
/*
* Do not consider all the reclaimable memory because we do not
* want to trash just for a single high order allocation which
* is even not guaranteed to appear even if __compaction_suitable
* is happy about the watermark check.
*/
available = zone_reclaimable_pages(zone) / order;
available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
compact_result = __compaction_suitable(zone, order, alloc_flags,
ac->highest_zoneidx, available);
if (compact_result != COMPACT_SKIPPED)
return true;
}
return false;
}
static enum compact_result
compact_zone(struct compact_control *cc, struct capture_control *capc)
{
enum compact_result ret;
unsigned long start_pfn = cc->zone->zone_start_pfn;
unsigned long end_pfn = zone_end_pfn(cc->zone);
unsigned long last_migrated_pfn;
const bool sync = cc->mode != MIGRATE_ASYNC;
bool update_cached;
/*
* These counters track activities during zone compaction. Initialize
* them before compacting a new zone.
*/
cc->total_migrate_scanned = 0;
cc->total_free_scanned = 0;
cc->nr_migratepages = 0;
cc->nr_freepages = 0;
INIT_LIST_HEAD(&cc->freepages);
INIT_LIST_HEAD(&cc->migratepages);
cc->migratetype = gfp_migratetype(cc->gfp_mask);
ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
cc->highest_zoneidx);
/* Compaction is likely to fail */
if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
return ret;
/* huh, compaction_suitable is returning something unexpected */
VM_BUG_ON(ret != COMPACT_CONTINUE);
/*
* Clear pageblock skip if there were failures recently and compaction
* is about to be retried after being deferred.
*/
if (compaction_restarting(cc->zone, cc->order))
__reset_isolation_suitable(cc->zone);
/*
* Setup to move all movable pages to the end of the zone. Used cached
* information on where the scanners should start (unless we explicitly
* want to compact the whole zone), but check that it is initialised
* by ensuring the values are within zone boundaries.
*/
cc->fast_start_pfn = 0;
if (cc->whole_zone) {
cc->migrate_pfn = start_pfn;
cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
} else {
cc->migrate_pfn = cc->zone->compact_cached_migrate_pfn[sync];
cc->free_pfn = cc->zone->compact_cached_free_pfn;
if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
cc->zone->compact_cached_free_pfn = cc->free_pfn;
}
if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
cc->migrate_pfn = start_pfn;
cc->zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
cc->zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
}
if (cc->migrate_pfn <= cc->zone->compact_init_migrate_pfn)
cc->whole_zone = true;
}
last_migrated_pfn = 0;
/*
* Migrate has separate cached PFNs for ASYNC and SYNC* migration on
* the basis that some migrations will fail in ASYNC mode. However,
* if the cached PFNs match and pageblocks are skipped due to having
* no isolation candidates, then the sync state does not matter.
* Until a pageblock with isolation candidates is found, keep the
* cached PFNs in sync to avoid revisiting the same blocks.
*/
update_cached = !sync &&
cc->zone->compact_cached_migrate_pfn[0] == cc->zone->compact_cached_migrate_pfn[1];
trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
cc->free_pfn, end_pfn, sync);
migrate_prep_local();
while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
int err;
unsigned long iteration_start_pfn = cc->migrate_pfn;
/*
* Avoid multiple rescans which can happen if a page cannot be
* isolated (dirty/writeback in async mode) or if the migrated
* pages are being allocated before the pageblock is cleared.
* The first rescan will capture the entire pageblock for
* migration. If it fails, it'll be marked skip and scanning
* will proceed as normal.
*/
cc->rescan = false;
if (pageblock_start_pfn(last_migrated_pfn) ==
pageblock_start_pfn(iteration_start_pfn)) {
cc->rescan = true;
}
switch (isolate_migratepages(cc)) {
case ISOLATE_ABORT:
ret = COMPACT_CONTENDED;
putback_movable_pages(&cc->migratepages);
cc->nr_migratepages = 0;
goto out;
case ISOLATE_NONE:
if (update_cached) {
cc->zone->compact_cached_migrate_pfn[1] =
cc->zone->compact_cached_migrate_pfn[0];
}
/*
* We haven't isolated and migrated anything, but
* there might still be unflushed migrations from
* previous cc->order aligned block.
*/
goto check_drain;
case ISOLATE_SUCCESS:
update_cached = false;
last_migrated_pfn = iteration_start_pfn;
}
err = migrate_pages(&cc->migratepages, compaction_alloc,
compaction_free, (unsigned long)cc, cc->mode,
MR_COMPACTION);
trace_mm_compaction_migratepages(cc->nr_migratepages, err,
&cc->migratepages);
/* All pages were either migrated or will be released */
cc->nr_migratepages = 0;
if (err) {
putback_movable_pages(&cc->migratepages);
/*
* migrate_pages() may return -ENOMEM when scanners meet
* and we want compact_finished() to detect it
*/
if (err == -ENOMEM && !compact_scanners_met(cc)) {
ret = COMPACT_CONTENDED;
goto out;
}
/*
* We failed to migrate at least one page in the current
* order-aligned block, so skip the rest of it.
*/
if (cc->direct_compaction &&
(cc->mode == MIGRATE_ASYNC)) {
cc->migrate_pfn = block_end_pfn(
cc->migrate_pfn - 1, cc->order);
/* Draining pcplists is useless in this case */
last_migrated_pfn = 0;
}
}
check_drain:
/*
* Has the migration scanner moved away from the previous
* cc->order aligned block where we migrated from? If yes,
* flush the pages that were freed, so that they can merge and
* compact_finished() can detect immediately if allocation
* would succeed.
*/
if (cc->order > 0 && last_migrated_pfn) {
unsigned long current_block_start =
block_start_pfn(cc->migrate_pfn, cc->order);
if (last_migrated_pfn < current_block_start) {
lru_add_drain_cpu_zone(cc->zone);
/* No more flushing until we migrate again */
last_migrated_pfn = 0;
}
}
/* Stop if a page has been captured */
if (capc && capc->page) {
ret = COMPACT_SUCCESS;
break;
}
}
out:
/*
* Release free pages and update where the free scanner should restart,
* so we don't leave any returned pages behind in the next attempt.
*/
if (cc->nr_freepages > 0) {
unsigned long free_pfn = release_freepages(&cc->freepages);
cc->nr_freepages = 0;
VM_BUG_ON(free_pfn == 0);
/* The cached pfn is always the first in a pageblock */
free_pfn = pageblock_start_pfn(free_pfn);
/*
* Only go back, not forward. The cached pfn might have been
* already reset to zone end in compact_finished()
*/
if (free_pfn > cc->zone->compact_cached_free_pfn)
cc->zone->compact_cached_free_pfn = free_pfn;
}
count_compact_events(COMPACTMIGRATE_SCANNED, cc->total_migrate_scanned);
count_compact_events(COMPACTFREE_SCANNED, cc->total_free_scanned);
trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
cc->free_pfn, end_pfn, sync, ret);
return ret;
}
static enum compact_result compact_zone_order(struct zone *zone, int order,
gfp_t gfp_mask, enum compact_priority prio,
unsigned int alloc_flags, int highest_zoneidx,
struct page **capture)
{
enum compact_result ret;
struct compact_control cc = {
.order = order,
.search_order = order,
.gfp_mask = gfp_mask,
.zone = zone,
.mode = (prio == COMPACT_PRIO_ASYNC) ?
MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
.alloc_flags = alloc_flags,
.highest_zoneidx = highest_zoneidx,
.direct_compaction = true,
.whole_zone = (prio == MIN_COMPACT_PRIORITY),
.ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
.ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
};
struct capture_control capc = {
.cc = &cc,
.page = NULL,
};
/*
* Make sure the structs are really initialized before we expose the
* capture control, in case we are interrupted and the interrupt handler
* frees a page.
*/
barrier();
WRITE_ONCE(current->capture_control, &capc);
ret = compact_zone(&cc, &capc);
VM_BUG_ON(!list_empty(&cc.freepages));
VM_BUG_ON(!list_empty(&cc.migratepages));
/*
* Make sure we hide capture control first before we read the captured
* page pointer, otherwise an interrupt could free and capture a page
* and we would leak it.
*/
WRITE_ONCE(current->capture_control, NULL);
*capture = READ_ONCE(capc.page);
return ret;
}
int sysctl_extfrag_threshold = 500;
/**
* try_to_compact_pages - Direct compact to satisfy a high-order allocation
* @gfp_mask: The GFP mask of the current allocation
* @order: The order of the current allocation
* @alloc_flags: The allocation flags of the current allocation
* @ac: The context of current allocation
* @prio: Determines how hard direct compaction should try to succeed
* @capture: Pointer to free page created by compaction will be stored here
*
* This is the main entry point for direct page compaction.
*/
enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
unsigned int alloc_flags, const struct alloc_context *ac,
enum compact_priority prio, struct page **capture)
{
int may_perform_io = gfp_mask & __GFP_IO;
struct zoneref *z;
struct zone *zone;
enum compact_result rc = COMPACT_SKIPPED;
/*
* Check if the GFP flags allow compaction - GFP_NOIO is really
* tricky context because the migration might require IO
*/
if (!may_perform_io)
return COMPACT_SKIPPED;
trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
/* Compact each zone in the list */
for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
ac->highest_zoneidx, ac->nodemask) {
enum compact_result status;
if (prio > MIN_COMPACT_PRIORITY
&& compaction_deferred(zone, order)) {
rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
continue;
}
status = compact_zone_order(zone, order, gfp_mask, prio,
alloc_flags, ac->highest_zoneidx, capture);
rc = max(status, rc);
/* The allocation should succeed, stop compacting */
if (status == COMPACT_SUCCESS) {
/*
* We think the allocation will succeed in this zone,
* but it is not certain, hence the false. The caller
* will repeat this with true if allocation indeed
* succeeds in this zone.
*/
compaction_defer_reset(zone, order, false);
break;
}
if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
status == COMPACT_PARTIAL_SKIPPED))
/*
* We think that allocation won't succeed in this zone
* so we defer compaction there. If it ends up
* succeeding after all, it will be reset.
*/
defer_compaction(zone, order);
/*
* We might have stopped compacting due to need_resched() in
* async compaction, or due to a fatal signal detected. In that
* case do not try further zones
*/
if ((prio == COMPACT_PRIO_ASYNC && need_resched())
|| fatal_signal_pending(current))
break;
}
return rc;
}
/*
* Compact all zones within a node till each zone's fragmentation score
* reaches within proactive compaction thresholds (as determined by the
* proactiveness tunable).
*
* It is possible that the function returns before reaching score targets
* due to various back-off conditions, such as, contention on per-node or
* per-zone locks.
*/
static void proactive_compact_node(pg_data_t *pgdat)
{
int zoneid;
struct zone *zone;
struct compact_control cc = {
.order = -1,
.mode = MIGRATE_SYNC_LIGHT,
.ignore_skip_hint = true,
.whole_zone = true,
.gfp_mask = GFP_KERNEL,
.proactive_compaction = true,
};
for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
zone = &pgdat->node_zones[zoneid];
if (!populated_zone(zone))
continue;
cc.zone = zone;
compact_zone(&cc, NULL);
VM_BUG_ON(!list_empty(&cc.freepages));
VM_BUG_ON(!list_empty(&cc.migratepages));
}
}
/* Compact all zones within a node */
static void compact_node(int nid)
{
pg_data_t *pgdat = NODE_DATA(nid);
int zoneid;
struct zone *zone;
struct compact_control cc = {
.order = -1,
.mode = MIGRATE_SYNC,
.ignore_skip_hint = true,
.whole_zone = true,
.gfp_mask = GFP_KERNEL,
};
for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
zone = &pgdat->node_zones[zoneid];
if (!populated_zone(zone))
continue;
cc.zone = zone;
compact_zone(&cc, NULL);
VM_BUG_ON(!list_empty(&cc.freepages));
VM_BUG_ON(!list_empty(&cc.migratepages));
}
}
/* Compact all nodes in the system */
static void compact_nodes(void)
{
int nid;
/* Flush pending updates to the LRU lists */
lru_add_drain_all();
for_each_online_node(nid)
compact_node(nid);
}
/* The written value is actually unused, all memory is compacted */
int sysctl_compact_memory;
/*
* Tunable for proactive compaction. It determines how
* aggressively the kernel should compact memory in the
* background. It takes values in the range [0, 100].
*/
unsigned int __read_mostly sysctl_compaction_proactiveness = 20;
/*
* This is the entry point for compacting all nodes via
* /proc/sys/vm/compact_memory
*/
int sysctl_compaction_handler(struct ctl_table *table, int write,
void *buffer, size_t *length, loff_t *ppos)
{
if (write)
compact_nodes();
return 0;
}
#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
static ssize_t sysfs_compact_node(struct device *dev,
struct device_attribute *attr,
const char *buf, size_t count)
{
int nid = dev->id;
if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
/* Flush pending updates to the LRU lists */
lru_add_drain_all();
compact_node(nid);
}
return count;
}
static DEVICE_ATTR(compact, 0200, NULL, sysfs_compact_node);
int compaction_register_node(struct node *node)
{
return device_create_file(&node->dev, &dev_attr_compact);
}
void compaction_unregister_node(struct node *node)
{
return device_remove_file(&node->dev, &dev_attr_compact);
}
#endif /* CONFIG_SYSFS && CONFIG_NUMA */
static inline bool kcompactd_work_requested(pg_data_t *pgdat)
{
return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
}
static bool kcompactd_node_suitable(pg_data_t *pgdat)
{
int zoneid;
struct zone *zone;
enum zone_type highest_zoneidx = pgdat->kcompactd_highest_zoneidx;
for (zoneid = 0; zoneid <= highest_zoneidx; zoneid++) {
zone = &pgdat->node_zones[zoneid];
if (!populated_zone(zone))
continue;
if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
highest_zoneidx) == COMPACT_CONTINUE)
return true;
}
return false;
}
static void kcompactd_do_work(pg_data_t *pgdat)
{
/*
* With no special task, compact all zones so that a page of requested
* order is allocatable.
*/
int zoneid;
struct zone *zone;
struct compact_control cc = {
.order = pgdat->kcompactd_max_order,
.search_order = pgdat->kcompactd_max_order,
.highest_zoneidx = pgdat->kcompactd_highest_zoneidx,
.mode = MIGRATE_SYNC_LIGHT,
.ignore_skip_hint = false,
.gfp_mask = GFP_KERNEL,
};
trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
cc.highest_zoneidx);
count_compact_event(KCOMPACTD_WAKE);
for (zoneid = 0; zoneid <= cc.highest_zoneidx; zoneid++) {
int status;
zone = &pgdat->node_zones[zoneid];
if (!populated_zone(zone))
continue;
if (compaction_deferred(zone, cc.order))
continue;
if (compaction_suitable(zone, cc.order, 0, zoneid) !=
COMPACT_CONTINUE)
continue;
if (kthread_should_stop())
return;
cc.zone = zone;
status = compact_zone(&cc, NULL);
if (status == COMPACT_SUCCESS) {
compaction_defer_reset(zone, cc.order, false);
} else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
/*
* Buddy pages may become stranded on pcps that could
* otherwise coalesce on the zone's free area for
* order >= cc.order. This is ratelimited by the
* upcoming deferral.
*/
drain_all_pages(zone);
/*
* We use sync migration mode here, so we defer like
* sync direct compaction does.
*/
defer_compaction(zone, cc.order);
}
count_compact_events(KCOMPACTD_MIGRATE_SCANNED,
cc.total_migrate_scanned);
count_compact_events(KCOMPACTD_FREE_SCANNED,
cc.total_free_scanned);
VM_BUG_ON(!list_empty(&cc.freepages));
VM_BUG_ON(!list_empty(&cc.migratepages));
}
/*
* Regardless of success, we are done until woken up next. But remember
* the requested order/highest_zoneidx in case it was higher/tighter
* than our current ones
*/
if (pgdat->kcompactd_max_order <= cc.order)
pgdat->kcompactd_max_order = 0;
if (pgdat->kcompactd_highest_zoneidx >= cc.highest_zoneidx)
pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
}
void wakeup_kcompactd(pg_data_t *pgdat, int order, int highest_zoneidx)
{
if (!order)
return;
if (pgdat->kcompactd_max_order < order)
pgdat->kcompactd_max_order = order;
if (pgdat->kcompactd_highest_zoneidx > highest_zoneidx)
pgdat->kcompactd_highest_zoneidx = highest_zoneidx;
/*
* Pairs with implicit barrier in wait_event_freezable()
* such that wakeups are not missed.
*/
if (!wq_has_sleeper(&pgdat->kcompactd_wait))
return;
if (!kcompactd_node_suitable(pgdat))
return;
trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
highest_zoneidx);
wake_up_interruptible(&pgdat->kcompactd_wait);
}
/*
* The background compaction daemon, started as a kernel thread
* from the init process.
*/
static int kcompactd(void *p)
{
pg_data_t *pgdat = (pg_data_t*)p;
struct task_struct *tsk = current;
unsigned int proactive_defer = 0;
const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
if (!cpumask_empty(cpumask))
set_cpus_allowed_ptr(tsk, cpumask);
set_freezable();
pgdat->kcompactd_max_order = 0;
pgdat->kcompactd_highest_zoneidx = pgdat->nr_zones - 1;
while (!kthread_should_stop()) {
unsigned long pflags;
trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
if (wait_event_freezable_timeout(pgdat->kcompactd_wait,
kcompactd_work_requested(pgdat),
msecs_to_jiffies(HPAGE_FRAG_CHECK_INTERVAL_MSEC))) {
psi_memstall_enter(&pflags);
kcompactd_do_work(pgdat);
psi_memstall_leave(&pflags);
continue;
}
/* kcompactd wait timeout */
if (should_proactive_compact_node(pgdat)) {
unsigned int prev_score, score;
if (proactive_defer) {
proactive_defer--;
continue;
}
prev_score = fragmentation_score_node(pgdat);
proactive_compact_node(pgdat);
score = fragmentation_score_node(pgdat);
/*
* Defer proactive compaction if the fragmentation
* score did not go down i.e. no progress made.
*/
proactive_defer = score < prev_score ?
0 : 1 << COMPACT_MAX_DEFER_SHIFT;
}
}
return 0;
}
/*
* This kcompactd start function will be called by init and node-hot-add.
* On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
*/
int kcompactd_run(int nid)
{
pg_data_t *pgdat = NODE_DATA(nid);
int ret = 0;
if (pgdat->kcompactd)
return 0;
pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
if (IS_ERR(pgdat->kcompactd)) {
pr_err("Failed to start kcompactd on node %d\n", nid);
ret = PTR_ERR(pgdat->kcompactd);
pgdat->kcompactd = NULL;
}
return ret;
}
/*
* Called by memory hotplug when all memory in a node is offlined. Caller must
* hold mem_hotplug_begin/end().
*/
void kcompactd_stop(int nid)
{
struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
if (kcompactd) {
kthread_stop(kcompactd);
NODE_DATA(nid)->kcompactd = NULL;
}
}
/*
* It's optimal to keep kcompactd on the same CPUs as their memory, but
* not required for correctness. So if the last cpu in a node goes
* away, we get changed to run anywhere: as the first one comes back,