Thread (6 messages) flat view 6 messages, 3 authors, 2021-02-09

Re: [PATCH] mm: page_alloc: update the COMPACT[STALL|FAIL] events properly

From: David Rientjes <rientjes@google.com>
Date: 2021-02-01 21:25:35
Also in: lkml

On Mon, 1 Feb 2021, Charan Teja Reddy wrote:
By defination, COMPACT[STALL|FAIL] events needs to be counted when there
s/defination/definition/
quoted hunk ↗ jump to hunk
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.

Signed-off-by: Charan Teja Reddy <redacted>
---
 mm/page_alloc.c | 2 ++
 1 file changed, 2 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 519a60d..531f244 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4152,6 +4152,8 @@ __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
This makes sense, I wonder if it would also be useful to check that 
page == NULL, either in try_to_compact_pages() or here for 
COMPACT_SKIPPED?
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