linux/mm/compaction.c
Mel Gorman 62997027ca mm: compaction: clear PG_migrate_skip based on compaction and reclaim activity
Compaction caches if a pageblock was scanned and no pages were isolated so
that the pageblocks can be skipped in the future to reduce scanning.  This
information is not cleared by the page allocator based on activity due to
the impact it would have to the page allocator fast paths.  Hence there is
a requirement that something clear the cache or pageblocks will be skipped
forever.  Currently the cache is cleared if there were a number of recent
allocation failures and it has not been cleared within the last 5 seconds.
Time-based decisions like this are terrible as they have no relationship
to VM activity and is basically a big hammer.

Unfortunately, accurate heuristics would add cost to some hot paths so
this patch implements a rough heuristic.  There are two cases where the
cache is cleared.

1. If a !kswapd process completes a compaction cycle (migrate and free
   scanner meet), the zone is marked compact_blockskip_flush. When kswapd
   goes to sleep, it will clear the cache. This is expected to be the
   common case where the cache is cleared. It does not really matter if
   kswapd happens to be asleep or going to sleep when the flag is set as
   it will be woken on the next allocation request.

2. If there have been multiple failures recently and compaction just
   finished being deferred then a process will clear the cache and start a
   full scan.  This situation happens if there are multiple high-order
   allocation requests under heavy memory pressure.

The clearing of the PG_migrate_skip bits and other scans is inherently
racy but the race is harmless.  For allocations that can fail such as THP,
they will simply fail.  For requests that cannot fail, they will retry the
allocation.  Tests indicated that scanning rates were roughly similar to
when the time-based heuristic was used and the allocation success rates
were similar.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: Richard Davies <richard@arachsys.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2012-10-09 16:22:51 +09:00

1229 lines
33 KiB
C

/*
* 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/swap.h>
#include <linux/migrate.h>
#include <linux/compaction.h>
#include <linux/mm_inline.h>
#include <linux/backing-dev.h>
#include <linux/sysctl.h>
#include <linux/sysfs.h>
#include "internal.h"
#if defined CONFIG_COMPACTION || defined CONFIG_CMA
#define CREATE_TRACE_POINTS
#include <trace/events/compaction.h>
static unsigned long release_freepages(struct list_head *freelist)
{
struct page *page, *next;
unsigned long count = 0;
list_for_each_entry_safe(page, next, freelist, lru) {
list_del(&page->lru);
__free_page(page);
count++;
}
return count;
}
static void map_pages(struct list_head *list)
{
struct page *page;
list_for_each_entry(page, list, lru) {
arch_alloc_page(page, 0);
kernel_map_pages(page, 1, 1);
}
}
static inline bool migrate_async_suitable(int migratetype)
{
return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
}
#ifdef CONFIG_COMPACTION
/* 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);
}
/*
* 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 start_pfn = zone->zone_start_pfn;
unsigned long end_pfn = zone->zone_start_pfn + zone->spanned_pages;
unsigned long pfn;
zone->compact_cached_migrate_pfn = start_pfn;
zone->compact_cached_free_pfn = end_pfn;
zone->compact_blockskip_flush = false;
/* Walk the zone and mark every pageblock as suitable for isolation */
for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
struct page *page;
cond_resched();
if (!pfn_valid(pfn))
continue;
page = pfn_to_page(pfn);
if (zone != page_zone(page))
continue;
clear_pageblock_skip(page);
}
}
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);
}
}
/*
* 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 nr_isolated,
bool migrate_scanner)
{
struct zone *zone = cc->zone;
if (!page)
return;
if (!nr_isolated) {
unsigned long pfn = page_to_pfn(page);
set_pageblock_skip(page);
/* Update where compaction should restart */
if (migrate_scanner) {
if (!cc->finished_update_migrate &&
pfn > zone->compact_cached_migrate_pfn)
zone->compact_cached_migrate_pfn = pfn;
} else {
if (!cc->finished_update_free &&
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 void update_pageblock_skip(struct compact_control *cc,
struct page *page, unsigned long nr_isolated,
bool migrate_scanner)
{
}
#endif /* CONFIG_COMPACTION */
static inline bool should_release_lock(spinlock_t *lock)
{
return need_resched() || spin_is_contended(lock);
}
/*
* Compaction requires the taking of some coarse locks that are potentially
* very heavily contended. Check if the process needs to be scheduled or
* if the lock is contended. For async compaction, back out in the event
* if contention is severe. For sync compaction, schedule.
*
* Returns true if the lock is held.
* Returns false if the lock is released and compaction should abort
*/
static bool compact_checklock_irqsave(spinlock_t *lock, unsigned long *flags,
bool locked, struct compact_control *cc)
{
if (should_release_lock(lock)) {
if (locked) {
spin_unlock_irqrestore(lock, *flags);
locked = false;
}
/* async aborts if taking too long or contended */
if (!cc->sync) {
cc->contended = true;
return false;
}
cond_resched();
}
if (!locked)
spin_lock_irqsave(lock, *flags);
return true;
}
static inline bool compact_trylock_irqsave(spinlock_t *lock,
unsigned long *flags, struct compact_control *cc)
{
return compact_checklock_irqsave(lock, flags, false, cc);
}
/* Returns true if the page is within a block suitable for migration to */
static bool suitable_migration_target(struct page *page)
{
int migratetype = get_pageblock_migratetype(page);
/* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
return false;
/* If the page is a large free page, then allow migration */
if (PageBuddy(page) && page_order(page) >= pageblock_order)
return true;
/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
if (migrate_async_suitable(migratetype))
return true;
/* Otherwise skip the block */
return false;
}
static void compact_capture_page(struct compact_control *cc)
{
unsigned long flags;
int mtype, mtype_low, mtype_high;
if (!cc->page || *cc->page)
return;
/*
* For MIGRATE_MOVABLE allocations we capture a suitable page ASAP
* regardless of the migratetype of the freelist is is captured from.
* This is fine because the order for a high-order MIGRATE_MOVABLE
* allocation is typically at least a pageblock size and overall
* fragmentation is not impaired. Other allocation types must
* capture pages from their own migratelist because otherwise they
* could pollute other pageblocks like MIGRATE_MOVABLE with
* difficult to move pages and making fragmentation worse overall.
*/
if (cc->migratetype == MIGRATE_MOVABLE) {
mtype_low = 0;
mtype_high = MIGRATE_PCPTYPES;
} else {
mtype_low = cc->migratetype;
mtype_high = cc->migratetype + 1;
}
/* Speculatively examine the free lists without zone lock */
for (mtype = mtype_low; mtype < mtype_high; mtype++) {
int order;
for (order = cc->order; order < MAX_ORDER; order++) {
struct page *page;
struct free_area *area;
area = &(cc->zone->free_area[order]);
if (list_empty(&area->free_list[mtype]))
continue;
/* Take the lock and attempt capture of the page */
if (!compact_trylock_irqsave(&cc->zone->lock, &flags, cc))
return;
if (!list_empty(&area->free_list[mtype])) {
page = list_entry(area->free_list[mtype].next,
struct page, lru);
if (capture_free_page(page, cc->order, mtype)) {
spin_unlock_irqrestore(&cc->zone->lock,
flags);
*cc->page = page;
return;
}
}
spin_unlock_irqrestore(&cc->zone->lock, flags);
}
}
}
/*
* Isolate free pages onto a private freelist. Caller must hold zone->lock.
* 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 blockpfn,
unsigned long end_pfn,
struct list_head *freelist,
bool strict)
{
int nr_scanned = 0, total_isolated = 0;
struct page *cursor, *valid_page = NULL;
unsigned long nr_strict_required = end_pfn - blockpfn;
unsigned long flags;
bool locked = false;
cursor = pfn_to_page(blockpfn);
/* Isolate free pages. */
for (; blockpfn < end_pfn; blockpfn++, cursor++) {
int isolated, i;
struct page *page = cursor;
nr_scanned++;
if (!pfn_valid_within(blockpfn))
continue;
if (!valid_page)
valid_page = page;
if (!PageBuddy(page))
continue;
/*
* The zone lock must be held to isolate freepages.
* Unfortunately this is a very coarse lock and can be
* heavily contended if there are parallel allocations
* or parallel compactions. For async compaction do not
* spin on the lock and we acquire the lock as late as
* possible.
*/
locked = compact_checklock_irqsave(&cc->zone->lock, &flags,
locked, cc);
if (!locked)
break;
/* Recheck this is a suitable migration target under lock */
if (!strict && !suitable_migration_target(page))
break;
/* Recheck this is a buddy page under lock */
if (!PageBuddy(page))
continue;
/* Found a free page, break it into order-0 pages */
isolated = split_free_page(page);
if (!isolated && strict)
break;
total_isolated += isolated;
for (i = 0; i < isolated; i++) {
list_add(&page->lru, freelist);
page++;
}
/* If a page was split, advance to the end of it */
if (isolated) {
blockpfn += isolated - 1;
cursor += isolated - 1;
}
}
trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
/*
* 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 && nr_strict_required != total_isolated)
total_isolated = 0;
if (locked)
spin_unlock_irqrestore(&cc->zone->lock, flags);
/* Update the pageblock-skip if the whole pageblock was scanned */
if (blockpfn == end_pfn)
update_pageblock_skip(cc, valid_page, total_isolated, false);
return total_isolated;
}
/**
* isolate_freepages_range() - isolate free pages.
* @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_end_pfn;
LIST_HEAD(freelist);
for (pfn = start_pfn; pfn < end_pfn; pfn += isolated) {
if (!pfn_valid(pfn) || cc->zone != page_zone(pfn_to_page(pfn)))
break;
/*
* On subsequent iterations ALIGN() is actually not needed,
* but we keep it that we not to complicate the code.
*/
block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
block_end_pfn = min(block_end_pfn, end_pfn);
isolated = isolate_freepages_block(cc, pfn, block_end_pfn,
&freelist, 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).
*/
}
/* split_free_page does not map the pages */
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;
}
/* Update the number of anon and file isolated pages in the zone */
static void acct_isolated(struct zone *zone, bool locked, struct compact_control *cc)
{
struct page *page;
unsigned int count[2] = { 0, };
list_for_each_entry(page, &cc->migratepages, lru)
count[!!page_is_file_cache(page)]++;
/* If locked we can use the interrupt unsafe versions */
if (locked) {
__mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
__mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
} else {
mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
}
}
/* Similar to reclaim, but different enough that they don't share logic */
static bool too_many_isolated(struct zone *zone)
{
unsigned long active, inactive, isolated;
inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
zone_page_state(zone, NR_INACTIVE_ANON);
active = zone_page_state(zone, NR_ACTIVE_FILE) +
zone_page_state(zone, NR_ACTIVE_ANON);
isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
zone_page_state(zone, NR_ISOLATED_ANON);
return isolated > (inactive + active) / 2;
}
/**
* isolate_migratepages_range() - isolate all migrate-able pages in range.
* @zone: Zone pages are in.
* @cc: Compaction control structure.
* @low_pfn: The first PFN of the range.
* @end_pfn: The one-past-the-last PFN of the range.
*
* Isolate all pages that can be migrated from the range specified by
* [low_pfn, end_pfn). 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 then end_pfn).
*
* Assumes that cc->migratepages is empty and cc->nr_migratepages is
* zero.
*
* Apart from cc->migratepages and cc->nr_migratetypes this function
* does not modify any cc's fields, in particular it does not modify
* (or read for that matter) cc->migrate_pfn.
*/
unsigned long
isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
unsigned long low_pfn, unsigned long end_pfn)
{
unsigned long last_pageblock_nr = 0, pageblock_nr;
unsigned long nr_scanned = 0, nr_isolated = 0;
struct list_head *migratelist = &cc->migratepages;
isolate_mode_t mode = 0;
struct lruvec *lruvec;
unsigned long flags;
bool locked = false;
struct page *page = NULL, *valid_page = NULL;
/*
* 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(zone))) {
/* async migration should just abort */
if (!cc->sync)
return 0;
congestion_wait(BLK_RW_ASYNC, HZ/10);
if (fatal_signal_pending(current))
return 0;
}
/* Time to isolate some pages for migration */
cond_resched();
for (; low_pfn < end_pfn; low_pfn++) {
/* give a chance to irqs before checking need_resched() */
if (locked && !((low_pfn+1) % SWAP_CLUSTER_MAX)) {
if (should_release_lock(&zone->lru_lock)) {
spin_unlock_irqrestore(&zone->lru_lock, flags);
locked = false;
}
}
/*
* migrate_pfn does not necessarily start aligned to a
* pageblock. Ensure that pfn_valid is called when moving
* into a new MAX_ORDER_NR_PAGES range in case of large
* memory holes within the zone
*/
if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
if (!pfn_valid(low_pfn)) {
low_pfn += MAX_ORDER_NR_PAGES - 1;
continue;
}
}
if (!pfn_valid_within(low_pfn))
continue;
nr_scanned++;
/*
* Get the page and ensure the page is within the same zone.
* See the comment in isolate_freepages about overlapping
* nodes. It is deliberate that the new zone lock is not taken
* as memory compaction should not move pages between nodes.
*/
page = pfn_to_page(low_pfn);
if (page_zone(page) != zone)
continue;
if (!valid_page)
valid_page = page;
/* If isolation recently failed, do not retry */
pageblock_nr = low_pfn >> pageblock_order;
if (!isolation_suitable(cc, page))
goto next_pageblock;
/* Skip if free */
if (PageBuddy(page))
continue;
/*
* For async migration, also only scan in MOVABLE blocks. Async
* migration is optimistic to see if the minimum amount of work
* satisfies the allocation
*/
if (!cc->sync && last_pageblock_nr != pageblock_nr &&
!migrate_async_suitable(get_pageblock_migratetype(page))) {
cc->finished_update_migrate = true;
goto next_pageblock;
}
/* Check may be lockless but that's ok as we recheck later */
if (!PageLRU(page))
continue;
/*
* PageLRU is set. lru_lock normally excludes isolation
* splitting and collapsing (collapsing has already happened
* if PageLRU is set) but the lock is not necessarily taken
* here and it is wasteful to take it just to check transhuge.
* Check TransHuge without lock and skip the whole pageblock if
* it's either a transhuge or hugetlbfs page, as calling
* compound_order() without preventing THP from splitting the
* page underneath us may return surprising results.
*/
if (PageTransHuge(page)) {
if (!locked)
goto next_pageblock;
low_pfn += (1 << compound_order(page)) - 1;
continue;
}
/* Check if it is ok to still hold the lock */
locked = compact_checklock_irqsave(&zone->lru_lock, &flags,
locked, cc);
if (!locked || fatal_signal_pending(current))
break;
/* Recheck PageLRU and PageTransHuge under lock */
if (!PageLRU(page))
continue;
if (PageTransHuge(page)) {
low_pfn += (1 << compound_order(page)) - 1;
continue;
}
if (!cc->sync)
mode |= ISOLATE_ASYNC_MIGRATE;
lruvec = mem_cgroup_page_lruvec(page, zone);
/* Try isolate the page */
if (__isolate_lru_page(page, mode) != 0)
continue;
VM_BUG_ON(PageTransCompound(page));
/* Successfully isolated */
cc->finished_update_migrate = true;
del_page_from_lru_list(page, lruvec, page_lru(page));
list_add(&page->lru, migratelist);
cc->nr_migratepages++;
nr_isolated++;
/* Avoid isolating too much */
if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
++low_pfn;
break;
}
continue;
next_pageblock:
low_pfn += pageblock_nr_pages;
low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
last_pageblock_nr = pageblock_nr;
}
acct_isolated(zone, locked, cc);
if (locked)
spin_unlock_irqrestore(&zone->lru_lock, flags);
/* Update the pageblock-skip if the whole pageblock was scanned */
if (low_pfn == end_pfn)
update_pageblock_skip(cc, valid_page, nr_isolated, true);
trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
return low_pfn;
}
#endif /* CONFIG_COMPACTION || CONFIG_CMA */
#ifdef CONFIG_COMPACTION
/*
* 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 zone *zone,
struct compact_control *cc)
{
struct page *page;
unsigned long high_pfn, low_pfn, pfn, zone_end_pfn, end_pfn;
int nr_freepages = cc->nr_freepages;
struct list_head *freelist = &cc->freepages;
/*
* Initialise the free scanner. The starting point is where we last
* scanned from (or the end of the zone if starting). The low point
* is the end of the pageblock the migration scanner is using.
*/
pfn = cc->free_pfn;
low_pfn = cc->migrate_pfn + pageblock_nr_pages;
/*
* Take care that if the migration scanner is at the end of the zone
* that the free scanner does not accidentally move to the next zone
* in the next isolation cycle.
*/
high_pfn = min(low_pfn, pfn);
zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
/*
* 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 (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
pfn -= pageblock_nr_pages) {
unsigned long isolated;
if (!pfn_valid(pfn))
continue;
/*
* Check for overlapping nodes/zones. It's possible on some
* configurations to have a setup like
* node0 node1 node0
* i.e. it's possible that all pages within a zones range of
* pages do not belong to a single zone.
*/
page = pfn_to_page(pfn);
if (page_zone(page) != zone)
continue;
/* Check the block is suitable for migration */
if (!suitable_migration_target(page))
continue;
/* If isolation recently failed, do not retry */
if (!isolation_suitable(cc, page))
continue;
/* Found a block suitable for isolating free pages from */
isolated = 0;
end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn);
isolated = isolate_freepages_block(cc, pfn, end_pfn,
freelist, false);
nr_freepages += isolated;
/*
* Record the highest PFN we isolated pages from. When next
* looking for free pages, the search will restart here as
* page migration may have returned some pages to the allocator
*/
if (isolated) {
cc->finished_update_free = true;
high_pfn = max(high_pfn, pfn);
}
}
/* split_free_page does not map the pages */
map_pages(freelist);
cc->free_pfn = high_pfn;
cc->nr_freepages = nr_freepages;
}
/*
* 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,
int **result)
{
struct compact_control *cc = (struct compact_control *)data;
struct page *freepage;
/* Isolate free pages if necessary */
if (list_empty(&cc->freepages)) {
isolate_freepages(cc->zone, 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;
}
/*
* We cannot control nr_migratepages and nr_freepages fully when migration is
* running as migrate_pages() has no knowledge of compact_control. When
* migration is complete, we count the number of pages on the lists by hand.
*/
static void update_nr_listpages(struct compact_control *cc)
{
int nr_migratepages = 0;
int nr_freepages = 0;
struct page *page;
list_for_each_entry(page, &cc->migratepages, lru)
nr_migratepages++;
list_for_each_entry(page, &cc->freepages, lru)
nr_freepages++;
cc->nr_migratepages = nr_migratepages;
cc->nr_freepages = 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;
/*
* Isolate all pages that can be migrated from the block pointed to by
* the migrate scanner within compact_control.
*/
static isolate_migrate_t isolate_migratepages(struct zone *zone,
struct compact_control *cc)
{
unsigned long low_pfn, end_pfn;
/* Do not scan outside zone boundaries */
low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
/* Only scan within a pageblock boundary */
end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
/* Do not cross the free scanner or scan within a memory hole */
if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
cc->migrate_pfn = end_pfn;
return ISOLATE_NONE;
}
/* Perform the isolation */
low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
if (!low_pfn || cc->contended)
return ISOLATE_ABORT;
cc->migrate_pfn = low_pfn;
return ISOLATE_SUCCESS;
}
static int compact_finished(struct zone *zone,
struct compact_control *cc)
{
unsigned long watermark;
if (fatal_signal_pending(current))
return COMPACT_PARTIAL;
/* Compaction run completes if the migrate and free scanner meet */
if (cc->free_pfn <= cc->migrate_pfn) {
/*
* Mark that the PG_migrate_skip information should be cleared
* by kswapd when it goes to sleep. kswapd does not set the
* flag itself as the decision to be clear should be directly
* based on an allocation request.
*/
if (!current_is_kswapd())
zone->compact_blockskip_flush = true;
return COMPACT_COMPLETE;
}
/*
* order == -1 is expected when compacting via
* /proc/sys/vm/compact_memory
*/
if (cc->order == -1)
return COMPACT_CONTINUE;
/* Compaction run is not finished if the watermark is not met */
watermark = low_wmark_pages(zone);
watermark += (1 << cc->order);
if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
return COMPACT_CONTINUE;
/* Direct compactor: Is a suitable page free? */
if (cc->page) {
/* Was a suitable page captured? */
if (*cc->page)
return COMPACT_PARTIAL;
} else {
unsigned int order;
for (order = cc->order; order < MAX_ORDER; order++) {
struct free_area *area = &zone->free_area[cc->order];
/* Job done if page is free of the right migratetype */
if (!list_empty(&area->free_list[cc->migratetype]))
return COMPACT_PARTIAL;
/* Job done if allocation would set block type */
if (cc->order >= pageblock_order && area->nr_free)
return COMPACT_PARTIAL;
}
}
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_PARTIAL - If the allocation would succeed without compaction
* COMPACT_CONTINUE - If compaction should run now
*/
unsigned long compaction_suitable(struct zone *zone, int order)
{
int fragindex;
unsigned long watermark;
/*
* order == -1 is expected when compacting via
* /proc/sys/vm/compact_memory
*/
if (order == -1)
return COMPACT_CONTINUE;
/*
* Watermarks for order-0 must be met for compaction. Note the 2UL.
* This is because during migration, copies of pages need to be
* allocated and for a short time, the footprint is higher
*/
watermark = low_wmark_pages(zone) + (2UL << order);
if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
return COMPACT_SKIPPED;
/*
* fragmentation index determines if allocation failures are due to
* low memory or external fragmentation
*
* index of -1000 implies allocations might succeed depending on
* watermarks
* 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.
*/
fragindex = fragmentation_index(zone, order);
if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
return COMPACT_SKIPPED;
if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
0, 0))
return COMPACT_PARTIAL;
return COMPACT_CONTINUE;
}
static int compact_zone(struct zone *zone, struct compact_control *cc)
{
int ret;
unsigned long start_pfn = zone->zone_start_pfn;
unsigned long end_pfn = zone->zone_start_pfn + zone->spanned_pages;
ret = compaction_suitable(zone, cc->order);
switch (ret) {
case COMPACT_PARTIAL:
case COMPACT_SKIPPED:
/* Compaction is likely to fail */
return ret;
case COMPACT_CONTINUE:
/* Fall through to compaction */
;
}
/*
* Setup to move all movable pages to the end of the zone. Used cached
* information on where the scanners should start but check that it
* is initialised by ensuring the values are within zone boundaries.
*/
cc->migrate_pfn = zone->compact_cached_migrate_pfn;
cc->free_pfn = zone->compact_cached_free_pfn;
if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) {
cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1);
zone->compact_cached_free_pfn = cc->free_pfn;
}
if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) {
cc->migrate_pfn = start_pfn;
zone->compact_cached_migrate_pfn = cc->migrate_pfn;
}
/*
* Clear pageblock skip if there were failures recently and compaction
* is about to be retried after being deferred. kswapd does not do
* this reset as it'll reset the cached information when going to sleep.
*/
if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
__reset_isolation_suitable(zone);
migrate_prep_local();
while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
unsigned long nr_migrate, nr_remaining;
int err;
switch (isolate_migratepages(zone, cc)) {
case ISOLATE_ABORT:
ret = COMPACT_PARTIAL;
putback_lru_pages(&cc->migratepages);
cc->nr_migratepages = 0;
goto out;
case ISOLATE_NONE:
continue;
case ISOLATE_SUCCESS:
;
}
nr_migrate = cc->nr_migratepages;
err = migrate_pages(&cc->migratepages, compaction_alloc,
(unsigned long)cc, false,
cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC);
update_nr_listpages(cc);
nr_remaining = cc->nr_migratepages;
count_vm_event(COMPACTBLOCKS);
count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
if (nr_remaining)
count_vm_events(COMPACTPAGEFAILED, nr_remaining);
trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
nr_remaining);
/* Release LRU pages not migrated */
if (err) {
putback_lru_pages(&cc->migratepages);
cc->nr_migratepages = 0;
if (err == -ENOMEM) {
ret = COMPACT_PARTIAL;
goto out;
}
}
/* Capture a page now if it is a suitable size */
compact_capture_page(cc);
}
out:
/* Release free pages and check accounting */
cc->nr_freepages -= release_freepages(&cc->freepages);
VM_BUG_ON(cc->nr_freepages != 0);
return ret;
}
static unsigned long compact_zone_order(struct zone *zone,
int order, gfp_t gfp_mask,
bool sync, bool *contended,
struct page **page)
{
unsigned long ret;
struct compact_control cc = {
.nr_freepages = 0,
.nr_migratepages = 0,
.order = order,
.migratetype = allocflags_to_migratetype(gfp_mask),
.zone = zone,
.sync = sync,
.page = page,
};
INIT_LIST_HEAD(&cc.freepages);
INIT_LIST_HEAD(&cc.migratepages);
ret = compact_zone(zone, &cc);
VM_BUG_ON(!list_empty(&cc.freepages));
VM_BUG_ON(!list_empty(&cc.migratepages));
*contended = cc.contended;
return ret;
}
int sysctl_extfrag_threshold = 500;
/**
* try_to_compact_pages - Direct compact to satisfy a high-order allocation
* @zonelist: The zonelist used for the current allocation
* @order: The order of the current allocation
* @gfp_mask: The GFP mask of the current allocation
* @nodemask: The allowed nodes to allocate from
* @sync: Whether migration is synchronous or not
* @contended: Return value that is true if compaction was aborted due to lock contention
* @page: Optionally capture a free page of the requested order during compaction
*
* This is the main entry point for direct page compaction.
*/
unsigned long try_to_compact_pages(struct zonelist *zonelist,
int order, gfp_t gfp_mask, nodemask_t *nodemask,
bool sync, bool *contended, struct page **page)
{
enum zone_type high_zoneidx = gfp_zone(gfp_mask);
int may_enter_fs = gfp_mask & __GFP_FS;
int may_perform_io = gfp_mask & __GFP_IO;
struct zoneref *z;
struct zone *zone;
int rc = COMPACT_SKIPPED;
int alloc_flags = 0;
/* Check if the GFP flags allow compaction */
if (!order || !may_enter_fs || !may_perform_io)
return rc;
count_vm_event(COMPACTSTALL);
#ifdef CONFIG_CMA
if (allocflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
alloc_flags |= ALLOC_CMA;
#endif
/* Compact each zone in the list */
for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
nodemask) {
int status;
status = compact_zone_order(zone, order, gfp_mask, sync,
contended, page);
rc = max(status, rc);
/* If a normal allocation would succeed, stop compacting */
if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0,
alloc_flags))
break;
}
return rc;
}
/* Compact all zones within a node */
static int __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
{
int zoneid;
struct zone *zone;
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);
if (cc->order == -1 || !compaction_deferred(zone, cc->order))
compact_zone(zone, cc);
if (cc->order > 0) {
int ok = zone_watermark_ok(zone, cc->order,
low_wmark_pages(zone), 0, 0);
if (ok && cc->order >= zone->compact_order_failed)
zone->compact_order_failed = cc->order + 1;
/* Currently async compaction is never deferred. */
else if (!ok && cc->sync)
defer_compaction(zone, cc->order);
}
VM_BUG_ON(!list_empty(&cc->freepages));
VM_BUG_ON(!list_empty(&cc->migratepages));
}
return 0;
}
int compact_pgdat(pg_data_t *pgdat, int order)
{
struct compact_control cc = {
.order = order,
.sync = false,
.page = NULL,
};
return __compact_pgdat(pgdat, &cc);
}
static int compact_node(int nid)
{
struct compact_control cc = {
.order = -1,
.sync = true,
.page = NULL,
};
return __compact_pgdat(NODE_DATA(nid), &cc);
}
/* Compact all nodes in the system */
static int compact_nodes(void)
{
int nid;
/* Flush pending updates to the LRU lists */
lru_add_drain_all();
for_each_online_node(nid)
compact_node(nid);
return COMPACT_COMPLETE;
}
/* 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 */
int sysctl_compaction_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *length, loff_t *ppos)
{
if (write)
return compact_nodes();
return 0;
}
int sysctl_extfrag_handler(struct ctl_table *table, int write,
void __user *buffer, size_t *length, loff_t *ppos)
{
proc_dointvec_minmax(table, write, buffer, length, ppos);
return 0;
}
#if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
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, S_IWUSR, 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 */
#endif /* CONFIG_COMPACTION */