From: David Carlier <devnexen@gmail.com>
To: SJ Park <sj@kernel.org>
Cc: Aveline Noir <jm5905938@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
damon@lists.linux.dev, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/9] mm/damon/stat: avoid 32-bit overflow in idle percentiles
Date: Sat, 14 Nov 2026 18:10:34 +0000 [thread overview]
Message-ID: <20261114181034.2665113-1-devnexen@gmail.com> (raw)
In-Reply-To: <20261102150757.93058-5-sj@kernel.org>
Hi SJ, Aveline,
The value stored a few lines below has the same problem on 32-bit:
damon_stat_idletime(region) *
(long)c->attrs.aggr_interval / USEC_PER_MSEC;
The product is the region's idle time in microseconds, held in a 32-bit
long, so it wraps once a region has been idle for more than about 36
minutes, whatever the intervals are. The cold-end percentiles then come
out negative or wrong. Doing the multiply in s64 with div_s64() would
keep the sign and avoid it.
Hope it helps !
next prev parent reply other threads:[~2026-11-14 18:10 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-02 15:07 [PATCH 0/9] mm/damon: various fixes and cleanup of code, test, and docs SJ Park
2026-11-02 15:07 ` [PATCH 1/9] mm/damon/core: remove unnecessary zero-initialization in damon_new_ctx() SJ Park
2026-11-02 15:07 ` [PATCH 2/9] mm/damon/ops-common: align MMU notifier range when clearing PTE young bit SJ Park
2026-11-02 15:07 ` [PATCH 3/9] mm/damon/ops-common: align MMU notifier range when clearing PMD " SJ Park
2026-11-02 15:07 ` [PATCH 4/9] mm/damon/stat: avoid 32-bit overflow in idle percentiles SJ Park
2026-11-14 18:10 ` David Carlier [this message]
2026-11-02 15:07 ` [PATCH 5/9] mm/damon/{p,v}addr: skip folios already on the migration target node SJ Park
2026-11-03 14:09 ` SJ Park
2026-11-02 15:07 ` [PATCH 6/9] selftests/damon/sysfs.py: stop obsolete_target shells hanging the test SJ Park
2026-11-02 15:07 ` [PATCH 7/9] mm/damon/reclaim: fix typo and grammar SJ Park
2026-11-02 15:07 ` [PATCH 8/9] Docs/admin-guide/mm/damon/lru_sort: fix grammar and stlye SJ Park
2026-11-03 2:37 ` Daniel Pereira
2026-11-02 15:07 ` [PATCH 9/9] Docs/admin-guide/mm/damon/reclaim: document how to disable watermarks SJ Park
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