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From:   SeongJae Park <sj@kernel.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     SeongJae Park <sj@kernel.org>, damon@lists.linux.dev,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: [PATCH 1/2] mm/damon/core: copy nr_accesses when splitting region
Date:   Sun, 19 Nov 2023 17:15:28 +0000
Message-Id: <20231119171529.66863-1-sj@kernel.org>
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Regions split function ('damon_split_region_at()') is called at the
beginning of an aggregation interval, and when DAMOS applying the
actions and charging quota.  Because 'nr_accesses' fields of all regions
are reset at the beginning of each aggregation interval, and DAMOS was
applying the action at the end of each aggregation interval, there was
no need to copy the 'nr_accesses' field to the split-out region.

However, commit 42f994b71404 ("mm/damon/core: implement scheme-specific
apply interval") made DAMOS applies action on its own timing interval.
Hence, 'nr_accesses' should also copied to split-out regions, but the
commit didn't.  Fix it by copying it.

Fixes: 42f994b71404 ("mm/damon/core: implement scheme-specific apply interval")
Signed-off-by: SeongJae Park <sj@kernel.org>
---
Cc-ing stable@ is not needed, since the commit that introduced the issue has
merged in v6.7 merge window.

 mm/damon/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 6262d55904e7..ce1562783e7e 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1225,6 +1225,7 @@ static void damon_split_region_at(struct damon_target *t,
 	new->age = r->age;
 	new->last_nr_accesses = r->last_nr_accesses;
 	new->nr_accesses_bp = r->nr_accesses_bp;
+	new->nr_accesses = r->nr_accesses;
 
 	damon_insert_region(new, r, damon_next_region(r), t);
 }
-- 
2.34.1