+ mm-compaction-simplify-__alloc_pages_direct_compact-feedback-interface.patch added to -mm tree

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The patch titled
     Subject: mm, compaction: Simplify __alloc_pages_direct_compact feedback interface
has been added to the -mm tree.  Its filename is
     mm-compaction-simplify-__alloc_pages_direct_compact-feedback-interface.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-simplify-__alloc_pages_direct_compact-feedback-interface.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-simplify-__alloc_pages_direct_compact-feedback-interface.patch

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------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxxx>
Subject: mm, compaction: Simplify __alloc_pages_direct_compact feedback interface

__alloc_pages_direct_compact communicates potential back off by two
variables:

	- deferred_compaction tells that the compaction returned
	  COMPACT_DEFERRED
	- contended_compaction is set when there is a contention on
	  zone->lock resp. zone->lru_lock locks

__alloc_pages_slowpath then backs of for THP allocation requests to
prevent from long stalls.  This is rather messy and it would be much
cleaner to return a single compact result value and hide all the nasty
details into __alloc_pages_direct_compact.

This patch shouldn't introduce any functional changes.

Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Cc: Joonsoo Kim <js1304@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/page_alloc.c |   67 +++++++++++++++++++++-------------------------
 1 file changed, 31 insertions(+), 36 deletions(-)

diff -puN mm/page_alloc.c~mm-compaction-simplify-__alloc_pages_direct_compact-feedback-interface mm/page_alloc.c
--- a/mm/page_alloc.c~mm-compaction-simplify-__alloc_pages_direct_compact-feedback-interface
+++ a/mm/page_alloc.c
@@ -2948,29 +2948,21 @@ out:
 static struct page *
 __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 		int alloc_flags, const struct alloc_context *ac,
-		enum migrate_mode mode, int *contended_compaction,
-		bool *deferred_compaction)
+		enum migrate_mode mode, enum compact_result *compact_result)
 {
-	enum compact_result compact_result;
 	struct page *page;
+	int contended_compaction;
 
 	if (!order)
 		return NULL;
 
 	current->flags |= PF_MEMALLOC;
-	compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
-						mode, contended_compaction);
+	*compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac,
+						mode, &contended_compaction);
 	current->flags &= ~PF_MEMALLOC;
 
-	switch (compact_result) {
-	case COMPACT_DEFERRED:
-		*deferred_compaction = true;
-		/* fall-through */
-	case COMPACT_SKIPPED:
+	if (*compact_result <= COMPACT_INACTIVE)
 		return NULL;
-	default:
-		break;
-	}
 
 	/*
 	 * At least in one zone compaction wasn't deferred or skipped, so let's
@@ -2996,6 +2988,24 @@ __alloc_pages_direct_compact(gfp_t gfp_m
 	 */
 	count_vm_event(COMPACTFAIL);
 
+	/*
+	 * In all zones where compaction was attempted (and not
+	 * deferred or skipped), lock contention has been detected.
+	 * For THP allocation we do not want to disrupt the others
+	 * so we fallback to base pages instead.
+	 */
+	if (contended_compaction == COMPACT_CONTENDED_LOCK)
+		*compact_result = COMPACT_CONTENDED;
+
+	/*
+	 * If compaction was aborted due to need_resched(), we do not
+	 * want to further increase allocation latency, unless it is
+	 * khugepaged trying to collapse.
+	 */
+	if (contended_compaction == COMPACT_CONTENDED_SCHED
+		&& !(current->flags & PF_KTHREAD))
+		*compact_result = COMPACT_CONTENDED;
+
 	cond_resched();
 
 	return NULL;
@@ -3004,8 +3014,7 @@ __alloc_pages_direct_compact(gfp_t gfp_m
 static inline struct page *
 __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 		int alloc_flags, const struct alloc_context *ac,
-		enum migrate_mode mode, int *contended_compaction,
-		bool *deferred_compaction)
+		enum migrate_mode mode, enum compact_result *compact_result)
 {
 	return NULL;
 }
@@ -3254,8 +3263,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, u
 	unsigned long pages_reclaimed = 0;
 	unsigned long did_some_progress;
 	enum migrate_mode migration_mode = MIGRATE_ASYNC;
-	bool deferred_compaction = false;
-	int contended_compaction = COMPACT_CONTENDED_NONE;
+	enum compact_result compact_result;
 	int no_progress_loops = 0;
 
 	/*
@@ -3354,8 +3362,7 @@ retry:
 	 */
 	page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags, ac,
 					migration_mode,
-					&contended_compaction,
-					&deferred_compaction);
+					&compact_result);
 	if (page)
 		goto got_pg;
 
@@ -3368,25 +3375,14 @@ retry:
 		 * to heavily disrupt the system, so we fail the allocation
 		 * instead of entering direct reclaim.
 		 */
-		if (deferred_compaction)
-			goto nopage;
-
-		/*
-		 * In all zones where compaction was attempted (and not
-		 * deferred or skipped), lock contention has been detected.
-		 * For THP allocation we do not want to disrupt the others
-		 * so we fallback to base pages instead.
-		 */
-		if (contended_compaction == COMPACT_CONTENDED_LOCK)
+		if (compact_result == COMPACT_DEFERRED)
 			goto nopage;
 
 		/*
-		 * If compaction was aborted due to need_resched(), we do not
-		 * want to further increase allocation latency, unless it is
-		 * khugepaged trying to collapse.
+		 * Compaction is contended so rather back off than cause
+		 * excessive stalls.
 		 */
-		if (contended_compaction == COMPACT_CONTENDED_SCHED
-			&& !(current->flags & PF_KTHREAD))
+		if(compact_result == COMPACT_CONTENDED)
 			goto nopage;
 	}
 
@@ -3446,8 +3442,7 @@ noretry:
 	 */
 	page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags,
 					    ac, migration_mode,
-					    &contended_compaction,
-					    &deferred_compaction);
+					    &compact_result);
 	if (page)
 		goto got_pg;
 nopage:
_

Patches currently in -mm which might be from mhocko@xxxxxxxx are

include-linux-nodemaskh-create-next_node_in-helper-fix.patch
mm-oom-rework-oom-detection.patch
mm-throttle-on-io-only-when-there-are-too-many-dirty-and-writeback-pages.patch
mm-compaction-change-compact_-constants-into-enum.patch
mm-compaction-cover-all-compaction-mode-in-compact_zone.patch
mm-compaction-distinguish-compact_deferred-from-compact_skipped.patch
mm-compaction-distinguish-between-full-and-partial-compact_complete.patch
mm-compaction-update-compaction_result-ordering.patch
mm-compaction-simplify-__alloc_pages_direct_compact-feedback-interface.patch
mm-compaction-abstract-compaction-feedback-to-helpers.patch
mm-oom-protect-costly-allocations-some-more.patch
mm-consider-compaction-feedback-also-for-costly-allocation.patch

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