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@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 31 insertions, 36 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ed62c4b90598..8bcc10616fab 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3185,29 +3185,21 @@ out:
 static struct page *
 __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
                 unsigned 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
@@ -3233,6 +3225,24 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
          */
         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;
@@ -3241,8 +3251,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
 static inline struct page *
 __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
                 unsigned 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;
 }
@@ -3387,8 +3396,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
         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;
 
         /*
          * In the slowpath, we sanity check order to avoid ever trying to
@@ -3475,8 +3483,7 @@ 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;
 
@@ -3489,25 +3496,14 @@ 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;
         }
 
@@ -3555,8 +3551,7 @@ 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: