Re: FAILED: patch "[PATCH] mm/damon/core: skip aging from repeated aggressive merging" failed to apply to 5.15-stable tree

[SJ Park <sj@kernel.org>]

On Tue, 08 Sep 2026 14:52:42 +0200 <gregkh@linuxfoundation.org> wrote:

> 
> The patch below does not apply to the 5.15-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
[...]
> ------------------ original commit in Linus's tree ------------------
> 
> From 0250dbe08c730d003ef9f484da56ae09a1ea0c4c Mon Sep 17 00:00:00 2001
> From: SJ Park <sj@kernel.org>
> Date: Sun, 12 Jul 2026 09:54:30 -0700
> Subject: [PATCH] mm/damon/core: skip aging from repeated aggressive merging
> 
> The number of DAMON regions could temporarily exceed the user-defined
> maximum number of regions limit for corner cases.  For example, users
> could lower the limit via runtime parameters update.  For such a case,
> kdamond_merge_regions() repeats merging regions in the case doubling the
> merge threshold.  The repeated merge operation could update the age of
> regions multiple times.  This corrupts the monitoring results.  Fix the
> issue by asking the merge operation to skip aging for the corner case.
> 
> The user impact is degradation of the monitoring quality.  The impact
> should be mild, since the degradation is only temporal, and it is not
> common to happen in realistic setups.
> 
> The issue was discovered [1,2] by Sashiko.
> 
> Link: https://lore.kernel.org/20260712165432.87609-1-sj@kernel.org
> Link: https://lore.kernel.org/20260621203548.10718-1-sj@kernel.org [1]
> Link: https://lore.kernel.org/20260709145425.96247-1-sj@kernel.org [2]
> Fixes: 310d6c15e910 ("mm/damon/core: merge regions aggressively when max_nr_regions is unmet")

The broken commit is backported to 5.15.y.  Seems this patch was tried to be
applied on 5.15.y for the reason.  However, this fix also depends on commit
fda504fade7f ("mm/damon/core: account age of target regions"), which is not in
5.15.y.  So, this patch doesn't need to be ported on 5.15.y.


Thanks,
SJ

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