[PATCH 5/5] mm: compaction: Abort async compaction if locks are contended or taking too long

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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-and-tested-by: Jim Schutt <jaschut@xxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
 include/linux/compaction.h |    4 +-
 mm/compaction.c            |  105 ++++++++++++++++++++++++++++++++++----------
 mm/internal.h              |    1 +
 mm/page_alloc.c            |   17 ++++---
 4 files changed, 96 insertions(+), 31 deletions(-)

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index fd20c15..0e38a1d 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -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, struct page **page);
+			bool sync, bool *contended, struct page **page);
 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, struct page **page)
+			bool sync, bool *contended, struct page **page)
 {
 	return COMPACT_CONTINUE;
 }
diff --git a/mm/compaction.c b/mm/compaction.c
index c2d0958..b95e263 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -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);
+}
+
 static void compact_capture_page(struct compact_control *cc)
 {
 	unsigned long flags;
@@ -87,7 +128,8 @@ static void compact_capture_page(struct compact_control *cc)
 				continue;
 
 			/* Take the lock and attempt capture of the page */
-			spin_lock_irqsave(&cc->zone->lock, flags);
+			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);
@@ -226,7 +268,7 @@ 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, };
@@ -234,8 +276,14 @@ 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 */
@@ -281,6 +329,8 @@ 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
@@ -300,25 +350,22 @@ 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
@@ -402,9 +449,10 @@ 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);
 
@@ -514,7 +562,16 @@ 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);
 			trace_mm_compaction_freepage_scanpfn(pfn);
@@ -837,8 +894,8 @@ out:
 }
 
 static unsigned long compact_zone_order(struct zone *zone,
-				 int order, gfp_t gfp_mask,
-				 bool sync, struct page **page)
+				 int order, gfp_t gfp_mask, bool sync,
+				 bool *contended, struct page **page)
 {
 	struct compact_control cc = {
 		.nr_freepages = 0,
@@ -848,6 +905,7 @@ static unsigned long compact_zone_order(struct zone *zone,
 		.zone = zone,
 		.sync = sync,
 		.page = page,
+		.contended = contended,
 	};
 	INIT_LIST_HEAD(&cc.freepages);
 	INIT_LIST_HEAD(&cc.migratepages);
@@ -869,7 +927,7 @@ 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, struct page **page)
+			bool sync, bool *contended, struct page **page)
 {
 	enum zone_type high_zoneidx = gfp_zone(gfp_mask);
 	int may_enter_fs = gfp_mask & __GFP_FS;
@@ -889,7 +947,8 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
 								nodemask) {
 		int status;
 
-		status = compact_zone_order(zone, order, gfp_mask, sync, page);
+		status = compact_zone_order(zone, order, gfp_mask, sync,
+						contended, page);
 		rc = max(status, rc);
 
 		/* If a normal allocation would succeed, stop compacting */
diff --git a/mm/internal.h b/mm/internal.h
index b03f05e..e549a7f 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -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 */
 	struct page **page;		/* Page captured of requested size */
 };
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d1759f5..373d05f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2114,7 +2114,7 @@ __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 = NULL;
@@ -2129,7 +2129,8 @@ __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, &page);
+					nodemask, sync_migration,
+					contended_compaction, &page);
 	current->flags &= ~PF_MEMALLOC;
 
 	/* If compaction captured a page, prep and use it */
@@ -2182,7 +2183,7 @@ __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;
@@ -2355,6 +2356,7 @@ __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
@@ -2451,6 +2453,7 @@ rebalance:
 					nodemask,
 					alloc_flags, preferred_zone,
 					migratetype, sync_migration,
+					&contended_compaction,
 					&deferred_compaction,
 					&did_some_progress);
 	if (page)
@@ -2460,10 +2463,11 @@ 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)
+	if (contended_compaction &&
+	    (gfp_mask & (__GFP_MOVABLE|__GFP_REPEAT)) == __GFP_MOVABLE)
 		goto nopage;
 
 	/* Try direct reclaim and then allocating */
@@ -2534,6 +2538,7 @@ rebalance:
 					nodemask,
 					alloc_flags, preferred_zone,
 					migratetype, sync_migration,
+					&contended_compaction,
 					&deferred_compaction,
 					&did_some_progress);
 		if (page)
-- 
1.7.9.2

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>


[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux]     [Linux OMAP]     [Linux MIPS]     [ECOS]     [Asterisk Internet PBX]     [Linux API]