Re: [PATCH 6.18.y v2] mm/damon/core: move static variable last_nr_regions to damon_ctx

[sashiko-bot@kernel.org]

> kdamond_split_regions() uses a static variable last_nr_regions, to infer
> if the region boundaries are too stable.  If it looks too stable, it
> does a more aggressive region split because it might be a fake stability
> coming from non-aggressive split.  Because the variable is static, the
> inference can be racy and wrong when multiple kdamonds are running in
> parallel.
> 
> The user impact is not critical.  No crash, no leak.  DAMON's
> best-effort monitoring accuracy can be degraded when multiple kdamonds
> are used in parallel and the workload has certain access patterns. Still
> it is a bug that is better to fix.
> 
> Move the variable into the damon_ctx struct to fix the problem.
> 
> Link: https://lore.kernel.org/20261025164808.152048-3-sj@kernel.org
> Fixes: 75c1c2b53c78 ("mm/damon/dbgfs: support multiple contexts")
> Signed-off-by: SJ Park <sj@kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Closes: https://sashiko.dev/#/bug/linux-eebfcdde-2881-48ef-8df1-e2019d2a47f2
> Cc: Fernand Sieber <sieberf@amazon.com>
> Cc: SeongJae Park <sjpark@amazon.de>
> Cc: <stable@vger.kernel.org> # 5.15.x
> (cherry picked from commit 26ae50a0901a44f7d50053f87dc38abd9f9a269c)
> Signed-off-by: SJ Park <sj@kernel.org>

Sashiko has reviewed this patch and found no issues.

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