linux-stable/mm/compaction.c
Mel Gorman 670105a256 mm: compaction: avoid 100% CPU usage during compaction when a task is killed
"howaboutsynergy" reported via kernel buzilla number 204165 that
compact_zone_order was consuming 100% CPU during a stress test for
prolonged periods of time.  Specifically the following command, which
should exit in 10 seconds, was taking an excessive time to finish while
the CPU was pegged at 100%.

  stress -m 220 --vm-bytes 1000000000 --timeout 10

Tracing indicated a pattern as follows

          stress-3923  [007]   519.106208: mm_compaction_isolate_migratepages: range=(0x70bb80 ~ 0x70bb80) nr_scanned=0 nr_taken=0
          stress-3923  [007]   519.106212: mm_compaction_isolate_migratepages: range=(0x70bb80 ~ 0x70bb80) nr_scanned=0 nr_taken=0
          stress-3923  [007]   519.106216: mm_compaction_isolate_migratepages: range=(0x70bb80 ~ 0x70bb80) nr_scanned=0 nr_taken=0
          stress-3923  [007]   519.106219: mm_compaction_isolate_migratepages: range=(0x70bb80 ~ 0x70bb80) nr_scanned=0 nr_taken=0
          stress-3923  [007]   519.106223: mm_compaction_isolate_migratepages: range=(0x70bb80 ~ 0x70bb80) nr_scanned=0 nr_taken=0
          stress-3923  [007]   519.106227: mm_compaction_isolate_migratepages: range=(0x70bb80 ~ 0x70bb80) nr_scanned=0 nr_taken=0
          stress-3923  [007]   519.106231: mm_compaction_isolate_migratepages: range=(0x70bb80 ~ 0x70bb80) nr_scanned=0 nr_taken=0
          stress-3923  [007]   519.106235: mm_compaction_isolate_migratepages: range=(0x70bb80 ~ 0x70bb80) nr_scanned=0 nr_taken=0
          stress-3923  [007]   519.106238: mm_compaction_isolate_migratepages: range=(0x70bb80 ~ 0x70bb80) nr_scanned=0 nr_taken=0
          stress-3923  [007]   519.106242: mm_compaction_isolate_migratepages: range=(0x70bb80 ~ 0x70bb80) nr_scanned=0 nr_taken=0

Note that compaction is entered in rapid succession while scanning and
isolating nothing.  The problem is that when a task that is compacting
receives a fatal signal, it retries indefinitely instead of exiting
while making no progress as a fatal signal is pending.

It's not easy to trigger this condition although enabling zswap helps on
the basis that the timing is altered.  A very small window has to be hit
for the problem to occur (signal delivered while compacting and
isolating a PFN for migration that is not aligned to SWAP_CLUSTER_MAX).

This was reproduced locally -- 16G single socket system, 8G swap, 30%
zswap configured, vm-bytes 22000000000 using Colin Kings stress-ng
implementation from github running in a loop until the problem hits).
Tracing recorded the problem occurring almost 200K times in a short
window.  With this patch, the problem hit 4 times but the task existed
normally instead of consuming CPU.

This problem has existed for some time but it was made worse by commit
cf66f0700c ("mm, compaction: do not consider a need to reschedule as
contention").  Before that commit, if the same condition was hit then
locks would be quickly contended and compaction would exit that way.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204165
Link: http://lkml.kernel.org/r/20190718085708.GE24383@techsingularity.net
Fixes: cf66f0700c ("mm, compaction: do not consider a need to reschedule as contention")
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>	[5.1+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-08-03 07:02:00 -07:00

2744 lines
75 KiB
C

// 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)
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(!PageLocked(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_limit compactions are skipped up
* to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
*/
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 */
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;
if (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 */
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 consistenly 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_page = pfn_to_online_page(max(block_pfn, zone->zone_start_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_nr_pages;
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)
{
/* 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 = page_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;
bool locked = false;
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))) {
/* 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)
&& compact_unlock_should_abort(&pgdat->lru_lock,
flags, &locked, cc)) {
low_pfn = 0;
goto fatal_pending;
}
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;
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 = page_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. 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)) {
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) {
spin_unlock_irqrestore(&pgdat->lru_lock,
flags);
locked = false;
}
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;
/* If we already hold the lock, we can skip some rechecking */
if (!locked) {
locked = compact_lock_irqsave(&pgdat->lru_lock,
&flags, cc);
/* Try get exclusive access under lock */
if (!skip_updated) {
skip_updated = true;
if (test_and_set_skip(cc, page, low_pfn))
goto isolate_abort;
}
/* Recheck PageLRU and PageCompound under lock */
if (!PageLRU(page))
goto isolate_fail;
/*
* 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))) {
low_pfn += (1UL << compound_order(page)) - 1;
goto isolate_fail;
}
}
lruvec = mem_cgroup_page_lruvec(page, pgdat);
/* Try isolate the page */
if (__isolate_lru_page(page, isolate_mode) != 0)
goto isolate_fail;
VM_BUG_ON_PAGE(PageCompound(page), page);
/* Successfully isolated */
del_page_from_lru_list(page, lruvec, page_lru(page));
inc_node_page_state(page,
NR_ISOLATED_ANON + page_is_file_cache(page));
isolate_success:
list_add(&page->lru, &cc->migratepages);
cc->nr_migratepages++;
nr_isolated++;
/*
* 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:
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) {
spin_unlock_irqrestore(&pgdat->lru_lock, flags);
locked = false;
}
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;
isolate_abort:
if (locked)
spin_unlock_irqrestore(&pgdat->lru_lock, flags);
/*
* 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 (page_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 = pfn_to_page(pfn);
/* 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 = pageblock_start_pfn(pfn);
end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone)) - 1;
/* 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, high_pfn = 0, 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;
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 = pageblock_start_pfn(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 pessemistic 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 = pfn_to_page(min_pfn);
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
* 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.
*/
int sysctl_compact_unevictable_allowed __read_mostly = 1;
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;
/* 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 && pfn == cc->migrate_pfn && 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;
nr_scanned++;
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)) {
if (list_is_last(freelist, &freepage->lru))
break;
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;
set_pageblock_skip(freepage);
break;
}
if (nr_scanned >= limit) {
cc->fast_search_fail++;
move_freelist_tail(freelist, 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 (pfn == cc->migrate_pfn)
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 zone *zone,
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 < zone->zone_start_pfn)
block_start_pfn = 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,
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 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 (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;
}
}
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;
}
/*
* 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
*/
static enum compact_result __compaction_suitable(struct zone *zone, int order,
unsigned int alloc_flags,
int classzone_idx,
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, classzone_idx,
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 classzone_idx 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, classzone_idx,
ALLOC_CMA, wmark_target))
return COMPACT_SKIPPED;
return COMPACT_CONTINUE;
}
enum compact_result compaction_suitable(struct zone *zone, int order,
unsigned int alloc_flags,
int classzone_idx)
{
enum compact_result ret;
int fragindex;
ret = __compaction_suitable(zone, order, alloc_flags, classzone_idx,
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->high_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_classzone_idx(ac), 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;
cc->migratetype = gfpflags_to_migratetype(cc->gfp_mask);
ret = compaction_suitable(cc->zone, cc->order, cc->alloc_flags,
cc->classzone_idx);
/* 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 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(start_pfn)) {
cc->rescan = true;
}
switch (isolate_migratepages(cc->zone, cc)) {
case ISOLATE_ABORT:
ret = COMPACT_CONTENDED;
putback_movable_pages(&cc->migratepages);
cc->nr_migratepages = 0;
last_migrated_pfn = 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 = 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) {
int cpu;
unsigned long current_block_start =
block_start_pfn(cc->migrate_pfn, cc->order);
if (last_migrated_pfn < current_block_start) {
cpu = get_cpu();
lru_add_drain_cpu(cpu);
drain_local_pages(cc->zone);
put_cpu();
/* 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 classzone_idx,
struct page **capture)
{
enum compact_result ret;
struct compact_control cc = {
.nr_freepages = 0,
.nr_migratepages = 0,
.total_migrate_scanned = 0,
.total_free_scanned = 0,
.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,
.classzone_idx = classzone_idx,
.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,
};
if (capture)
current->capture_control = &capc;
INIT_LIST_HEAD(&cc.freepages);
INIT_LIST_HEAD(&cc.migratepages);
ret = compact_zone(&cc, &capc);
VM_BUG_ON(!list_empty(&cc.freepages));
VM_BUG_ON(!list_empty(&cc.migratepages));
*capture = capc.page;
current->capture_control = NULL;
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
*
* 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->high_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_classzone_idx(ac), 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 */
static void compact_node(int nid)
{
pg_data_t *pgdat = NODE_DATA(nid);
int zoneid;
struct zone *zone;
struct compact_control cc = {
.order = -1,
.total_migrate_scanned = 0,
.total_free_scanned = 0,
.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.nr_freepages = 0;
cc.nr_migratepages = 0;
cc.zone = zone;
INIT_LIST_HEAD(&cc.freepages);
INIT_LIST_HEAD(&cc.migratepages);
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;
/*
* 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 __user *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 classzone_idx = pgdat->kcompactd_classzone_idx;
for (zoneid = 0; zoneid <= classzone_idx; zoneid++) {
zone = &pgdat->node_zones[zoneid];
if (!populated_zone(zone))
continue;
if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
classzone_idx) == 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,
.total_migrate_scanned = 0,
.total_free_scanned = 0,
.classzone_idx = pgdat->kcompactd_classzone_idx,
.mode = MIGRATE_SYNC_LIGHT,
.ignore_skip_hint = false,
.gfp_mask = GFP_KERNEL,
};
trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
cc.classzone_idx);
count_compact_event(KCOMPACTD_WAKE);
for (zoneid = 0; zoneid <= cc.classzone_idx; 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;
cc.nr_freepages = 0;
cc.nr_migratepages = 0;
cc.total_migrate_scanned = 0;
cc.total_free_scanned = 0;
cc.zone = zone;
INIT_LIST_HEAD(&cc.freepages);
INIT_LIST_HEAD(&cc.migratepages);
if (kthread_should_stop())
return;
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/classzone_idx 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_classzone_idx >= cc.classzone_idx)
pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
}
void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx)
{
if (!order)
return;
if (pgdat->kcompactd_max_order < order)
pgdat->kcompactd_max_order = order;
if (pgdat->kcompactd_classzone_idx > classzone_idx)
pgdat->kcompactd_classzone_idx = classzone_idx;
/*
* 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,
classzone_idx);
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;
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_classzone_idx = pgdat->nr_zones - 1;
while (!kthread_should_stop()) {
unsigned long pflags;
trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
wait_event_freezable(pgdat->kcompactd_wait,
kcompactd_work_requested(pgdat));
psi_memstall_enter(&pflags);
kcompactd_do_work(pgdat);
psi_memstall_leave(&pflags);
}
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,
* restore their cpu bindings.
*/
static int kcompactd_cpu_online(unsigned int cpu)
{
int nid;
for_each_node_state(nid, N_MEMORY) {
pg_data_t *pgdat = NODE_DATA(nid);
const struct cpumask *mask;
mask = cpumask_of_node(pgdat->node_id);
if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
/* One of our CPUs online: restore mask */
set_cpus_allowed_ptr(pgdat->kcompactd, mask);
}
return 0;
}
static int __init kcompactd_init(void)
{
int nid;
int ret;
ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
"mm/compaction:online",
kcompactd_cpu_online, NULL);
if (ret < 0) {
pr_err("kcompactd: failed to register hotplug callbacks.\n");
return ret;
}
for_each_node_state(nid, N_MEMORY)
kcompactd_run(nid);
return 0;
}
subsys_initcall(kcompactd_init)
#endif /* CONFIG_COMPACTION */