Commit c67fe375 authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds

mm: compaction: Abort async compaction if locks are contended or taking too long

Jim Schutt reported a problem that pointed at compaction contending
heavily on locks.  The workload is straight-forward and in his own words;

	The systems in question have 24 SAS drives spread across 3 HBAs,
	running 24 Ceph OSD instances, one per drive.  FWIW these servers
	are dual-socket Intel 5675 Xeons w/48 GB memory.  I've got ~160
	Ceph Linux clients doing dd simultaneously to a Ceph file system
	backed by 12 of these servers.

Early in the test everything looks fine

  procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu-------
   r  b       swpd       free       buff      cache   si   so    bi    bo   in   cs  us sy  id wa st
  31 15          0     287216        576   38606628    0    0     2  1158    2   14   1  3  95  0  0
  27 15          0     225288        576   38583384    0    0    18 2222016 203357 134876  11 56  17 15  0
  28 17          0     219256        576   38544736    0    0    11 2305932 203141 146296  11 49  23 17  0
   6 18          0     215596        576   38552872    0    0     7 2363207 215264 166502  12 45  22 20  0
  22 18          0     226984        576   38596404    0    0     3 2445741 223114 179527  12 43  23 22  0

and then it goes to pot

  procs -------------------memory------------------ ---swap-- -----io---- --system-- -----cpu-------
   r  b       swpd       free       buff      cache   si   so    bi    bo   in   cs  us sy  id wa st
  163  8          0     464308        576   36791368    0    0    11 22210  866  536   3 13  79  4  0
  207 14          0     917752        576   36181928    0    0   712 1345376 134598 47367   7 90   1  2  0
  123 12          0     685516        576   36296148    0    0   429 1386615 158494 60077   8 84   5  3  0
  123 12          0     598572        576   36333728    0    0  1107 1233281 147542 62351   7 84   5  4  0
  622  7          0     660768        576   36118264    0    0   557 1345548 151394 59353   7 85   4  3  0
  223 11          0     283960        576   36463868    0    0    46 1107160 121846 33006   6 93   1  1  0

Note that system CPU usage is very high blocks being written out has
dropped by 42%. He analysed this with perf and found

  perf record -g -a sleep 10
  perf report --sort symbol --call-graph fractal,5
    34.63%  [k] _raw_spin_lock_irqsave
            |
            |--97.30%-- isolate_freepages
            |          compaction_alloc
            |          unmap_and_move
            |          migrate_pages
            |          compact_zone
            |          compact_zone_order
            |          try_to_compact_pages
            |          __alloc_pages_direct_compact
            |          __alloc_pages_slowpath
            |          __alloc_pages_nodemask
            |          alloc_pages_vma
            |          do_huge_pmd_anonymous_page
            |          handle_mm_fault
            |          do_page_fault
            |          page_fault
            |          |
            |          |--87.39%-- skb_copy_datagram_iovec
            |          |          tcp_recvmsg
            |          |          inet_recvmsg
            |          |          sock_recvmsg
            |          |          sys_recvfrom
            |          |          system_call
            |          |          __recv
            |          |          |
            |          |           --100.00%-- (nil)
            |          |
            |           --12.61%-- memcpy
             --2.70%-- [...]

There was other data but primarily it is all showing that compaction is
contended heavily on the zone->lock and zone->lru_lock.

commit [b2eef8c0: mm: compaction: minimise the time IRQs are disabled
while isolating pages for migration] noted that it was possible for
migration to hold the lru_lock for an excessive amount of time. Very
broadly speaking this patch expands the concept.

This patch introduces compact_checklock_irqsave() to check if a lock
is contended or the process needs to be scheduled. If either condition
is true then async compaction is aborted and the caller is informed.
The page allocator will fail a THP allocation if compaction failed due
to contention. This patch also introduces compact_trylock_irqsave()
which will acquire the lock only if it is not contended and the process
does not need to schedule.
Reported-by: default avatarJim Schutt <jaschut@sandia.gov>
Tested-by: default avatarJim Schutt <jaschut@sandia.gov>
Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent de74f1cc
......@@ -22,7 +22,7 @@ extern int sysctl_extfrag_handler(struct ctl_table *table, int write,
extern int fragmentation_index(struct zone *zone, unsigned int order);
extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
int order, gfp_t gfp_mask, nodemask_t *mask,
bool sync);
bool sync, bool *contended);
extern int compact_pgdat(pg_data_t *pgdat, int order);
extern unsigned long compaction_suitable(struct zone *zone, int order);
......@@ -64,7 +64,7 @@ static inline bool compaction_deferred(struct zone *zone, int order)
#else
static inline unsigned long try_to_compact_pages(struct zonelist *zonelist,
int order, gfp_t gfp_mask, nodemask_t *nodemask,
bool sync)
bool sync, bool *contended)
{
return COMPACT_CONTINUE;
}
......
......@@ -50,6 +50,47 @@ static inline bool migrate_async_suitable(int migratetype)
return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
}
/*
* 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 (need_resched() || spin_is_contended(lock)) {
if (locked) {
spin_unlock_irqrestore(lock, *flags);
locked = false;
}
/* async aborts if taking too long or contended */
if (!cc->sync) {
if (cc->contended)
*cc->contended = true;
return false;
}
cond_resched();
if (fatal_signal_pending(current))
return false;
}
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);
}
/*
* 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
......@@ -173,7 +214,7 @@ isolate_freepages_range(unsigned long start_pfn, unsigned long end_pfn)
}
/* Update the number of anon and file isolated pages in the zone */
static void acct_isolated(struct zone *zone, struct compact_control *cc)
static void acct_isolated(struct zone *zone, bool locked, struct compact_control *cc)
{
struct page *page;
unsigned int count[2] = { 0, };
......@@ -181,8 +222,14 @@ static void acct_isolated(struct zone *zone, struct compact_control *cc)
list_for_each_entry(page, &cc->migratepages, lru)
count[!!page_is_file_cache(page)]++;
__mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
__mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
/* 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 */
......@@ -228,6 +275,8 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
struct list_head *migratelist = &cc->migratepages;
isolate_mode_t mode = 0;
struct lruvec *lruvec;
unsigned long flags;
bool locked;
/*
* Ensure that there are not too many pages isolated from the LRU
......@@ -247,25 +296,22 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
/* Time to isolate some pages for migration */
cond_resched();
spin_lock_irq(&zone->lru_lock);
spin_lock_irqsave(&zone->lru_lock, flags);
locked = true;
for (; low_pfn < end_pfn; low_pfn++) {
struct page *page;
bool locked = true;
/* give a chance to irqs before checking need_resched() */
if (!((low_pfn+1) % SWAP_CLUSTER_MAX)) {
spin_unlock_irq(&zone->lru_lock);
spin_unlock_irqrestore(&zone->lru_lock, flags);
locked = false;
}
if (need_resched() || spin_is_contended(&zone->lru_lock)) {
if (locked)
spin_unlock_irq(&zone->lru_lock);
cond_resched();
spin_lock_irq(&zone->lru_lock);
if (fatal_signal_pending(current))
break;
} else if (!locked)
spin_lock_irq(&zone->lru_lock);
/* Check if it is ok to still hold the lock */
locked = compact_checklock_irqsave(&zone->lru_lock, &flags,
locked, cc);
if (!locked)
break;
/*
* migrate_pfn does not necessarily start aligned to a
......@@ -349,9 +395,10 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
}
}
acct_isolated(zone, cc);
acct_isolated(zone, locked, cc);
spin_unlock_irq(&zone->lru_lock);
if (locked)
spin_unlock_irqrestore(&zone->lru_lock, flags);
trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
......@@ -461,7 +508,16 @@ static void isolate_freepages(struct zone *zone,
* are disabled
*/
isolated = 0;
spin_lock_irqsave(&zone->lock, flags);
/*
* The zone lock must be held to isolate freepages. This
* 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
*/
if (!compact_trylock_irqsave(&zone->lock, &flags, cc))
break;
if (suitable_migration_target(page)) {
end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn);
isolated = isolate_freepages_block(pfn, end_pfn,
......@@ -773,7 +829,7 @@ out:
static unsigned long compact_zone_order(struct zone *zone,
int order, gfp_t gfp_mask,
bool sync)
bool sync, bool *contended)
{
struct compact_control cc = {
.nr_freepages = 0,
......@@ -782,6 +838,7 @@ static unsigned long compact_zone_order(struct zone *zone,
.migratetype = allocflags_to_migratetype(gfp_mask),
.zone = zone,
.sync = sync,
.contended = contended,
};
INIT_LIST_HEAD(&cc.freepages);
INIT_LIST_HEAD(&cc.migratepages);
......@@ -803,7 +860,7 @@ int sysctl_extfrag_threshold = 500;
*/
unsigned long try_to_compact_pages(struct zonelist *zonelist,
int order, gfp_t gfp_mask, nodemask_t *nodemask,
bool sync)
bool sync, bool *contended)
{
enum zone_type high_zoneidx = gfp_zone(gfp_mask);
int may_enter_fs = gfp_mask & __GFP_FS;
......@@ -827,7 +884,8 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
nodemask) {
int status;
status = compact_zone_order(zone, order, gfp_mask, sync);
status = compact_zone_order(zone, order, gfp_mask, sync,
contended);
rc = max(status, rc);
/* If a normal allocation would succeed, stop compacting */
......
......@@ -130,6 +130,7 @@ struct compact_control {
int order; /* order a direct compactor needs */
int migratetype; /* MOVABLE, RECLAIMABLE etc */
struct zone *zone;
bool *contended; /* True if a lock was contended */
};
unsigned long
......
......@@ -2102,7 +2102,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist, enum zone_type high_zoneidx,
nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
int migratetype, bool sync_migration,
bool *deferred_compaction,
bool *contended_compaction, bool *deferred_compaction,
unsigned long *did_some_progress)
{
struct page *page;
......@@ -2117,7 +2117,8 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
current->flags |= PF_MEMALLOC;
*did_some_progress = try_to_compact_pages(zonelist, order, gfp_mask,
nodemask, sync_migration);
nodemask, sync_migration,
contended_compaction);
current->flags &= ~PF_MEMALLOC;
if (*did_some_progress != COMPACT_SKIPPED) {
......@@ -2163,7 +2164,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist, enum zone_type high_zoneidx,
nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
int migratetype, bool sync_migration,
bool *deferred_compaction,
bool *contended_compaction, bool *deferred_compaction,
unsigned long *did_some_progress)
{
return NULL;
......@@ -2336,6 +2337,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
unsigned long did_some_progress;
bool sync_migration = false;
bool deferred_compaction = false;
bool contended_compaction = false;
/*
* In the slowpath, we sanity check order to avoid ever trying to
......@@ -2425,6 +2427,7 @@ rebalance:
nodemask,
alloc_flags, preferred_zone,
migratetype, sync_migration,
&contended_compaction,
&deferred_compaction,
&did_some_progress);
if (page)
......@@ -2434,10 +2437,11 @@ rebalance:
/*
* If compaction is deferred for high-order allocations, it is because
* sync compaction recently failed. In this is the case and the caller
* has requested the system not be heavily disrupted, fail the
* allocation now instead of entering direct reclaim
* requested a movable allocation that does not heavily disrupt the
* system then fail the allocation instead of entering direct reclaim.
*/
if (deferred_compaction && (gfp_mask & __GFP_NO_KSWAPD))
if ((deferred_compaction || contended_compaction) &&
(gfp_mask & __GFP_NO_KSWAPD))
goto nopage;
/* Try direct reclaim and then allocating */
......@@ -2508,6 +2512,7 @@ rebalance:
nodemask,
alloc_flags, preferred_zone,
migratetype, sync_migration,
&contended_compaction,
&deferred_compaction,
&did_some_progress);
if (page)
......
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