mm: compaction: update the COMPACT[STALL|FAIL] events properly

By definition, COMPACT[STALL|FAIL] events needs to be counted when there
is 'At least in one zone compaction wasn't deferred or skipped from the
direct compaction'.  And when compaction is skipped or deferred,
COMPACT_SKIPPED will be returned but it will still go and update these
compaction events which is wrong in the sense that COMPACT[STALL|FAIL]
is counted without even trying the compaction.

Correct this by skipping the counting of these events when
COMPACT_SKIPPED is returned for compaction.  This indirectly also avoid
the unnecessary try into the get_page_from_freelist() when compaction is
not even tried.

There is a corner case where compaction is skipped but still count
COMPACTSTALL event, which is that IRQ came and freed the page and the
same is captured in capture_control.

Link: https://lkml.kernel.org/r/1613151184-21213-1-git-send-email-charante@codeaurora.org
Signed-off-by: Charan Teja Reddy <charante@codeaurora.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/compaction.c b/mm/compaction.c
index 027eb79..1be7928 100644 (file)
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2529,6 +2529,14 @@ static enum compact_result compact_zone_order(struct zone *zone, int order,
         */
        WRITE_ONCE(current->capture_control, NULL);
        *capture = READ_ONCE(capc.page);
+       /*
+        * Technically, it is also possible that compaction is skipped but
+        * the page is still captured out of luck(IRQ came and freed the page).
+        * Returning COMPACT_SUCCESS in such cases helps in properly accounting
+        * the COMPACT[STALL|FAIL] when compaction is skipped.
+        */
+       if (*capture)
+               ret = COMPACT_SUCCESS;
 
        return ret;
 }

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 19cdd8a..64d4aae 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4204,6 +4204,8 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
        memalloc_noreclaim_restore(noreclaim_flag);
        psi_memstall_leave(&pflags);
 
+       if (*compact_result == COMPACT_SKIPPED)
+               return NULL;
        /*
         * At least in one zone compaction wasn't deferred or skipped, so let's
         * count a compaction stall