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0250dbe08c
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: 310d6c15e9 ("mm/damon/core: merge regions aggressively when max_nr_regions is unmet")
Signed-off-by: SJ Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.10
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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