+ mm-compaction-update-the-compact-events-properly.patch added to -mm tree

+ mm-compaction-update-the-compact-events-properly.patch added to -mm tree

[akpm]

The patch titled
     Subject: mm: compaction: update the COMPACT[STALL|FAIL] events properly
has been added to the -mm tree.  Its filename is
     mm-compaction-update-the-compact-events-properly.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/mm-compaction-update-the-compact-events-properly.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/mm-compaction-update-the-compact-events-properly.patch

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------------------------------------------------------
From: Charan Teja Reddy <charante@codeaurora.org>
Subject: 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>
---

 mm/compaction.c |    8 ++++++++
 mm/page_alloc.c |    2 ++
 2 files changed, 10 insertions(+)

--- a/mm/compaction.c~mm-compaction-update-the-compact-events-properly
+++ a/mm/compaction.c
@@ -2494,6 +2494,14 @@ static enum compact_result compact_zone_
 	 */
 	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;
 }
--- a/mm/page_alloc.c~mm-compaction-update-the-compact-events-properly
+++ a/mm/page_alloc.c
@@ -4181,6 +4181,8 @@ __alloc_pages_direct_compact(gfp_t gfp_m
 	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
_

Patches currently in -mm which might be from charante@codeaurora.org are

mm-compaction-update-the-compact-events-properly.patch