From 0284dff76e87fc47a1055080d4e8540b41d096b2 Mon Sep 17 00:00:00 2001 From: Jaeyeon Lee Date: Mon, 5 Oct 2026 23:52:05 -0700 Subject: [PATCH] mm/damon/ops-common: fix age_in_sec overflow on 32-bit Patch series "mm/damon: fix a minor bug, clean code, and add a test". Patch 1 from Jaeyeon Lee fixes a minor overflow issue in DAMOS. Patch 2 from Gregory Price (Meta) cleans up the code for handling of hugetlb pages. Patch 3 from Liew Rui Yan adds a kunit test for a recently fixed bug. This patch (of 3): damon_hot_score() calculates the age of a region by multiplying r->age and the aggregation interval. On 32-bit architectures, unsigned long is 32 bits, so the multiplication overflows once the age exceeds about 4295 seconds. Then old regions are scored as if they were young. Fix it by doing the calculation in 64-bit arithmetic using div_u64(). Also make age_in_sec u64, so the result is not truncated back to 32 bits. The issue was discovered [1] by Sashiko. Link: https://lore.kernel.org/20261006065209.41507-1-sj@kernel.org Link: https://lore.kernel.org/20261006065209.41507-2-sj@kernel.org Link: https://lore.kernel.org/20260623011652.1354-1-sj@kernel.org [1] Fixes: 198f0f4c58b9 ("mm/damon/vaddr,paddr: support pageout prioritization") Signed-off-by: Jaeyeon Lee Signed-off-by: SJ Park Signed-off-by: Andrew Morton Reviewed-by: SJ Park Assisted-by: LLM --- mm/damon/ops-common.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/damon/ops-common.c b/mm/damon/ops-common.c index 77366f42b3e5..7a7429359dc8 100644 --- a/mm/damon/ops-common.c +++ b/mm/damon/ops-common.c @@ -164,7 +164,7 @@ int damon_hot_score(struct damon_ctx *c, struct damon_region *r, struct damos *s) { int freq_subscore; - unsigned int age_in_sec; + u64 age_in_sec; int age_in_log, age_subscore; unsigned int freq_weight = s->quota.weight_nr_accesses; unsigned int age_weight = s->quota.weight_age; @@ -174,7 +174,8 @@ int damon_hot_score(struct damon_ctx *c, struct damon_region *r, DAMON_MAX_SUBSCORE, damon_nr_samples_per_aggr(&c->attrs)); - age_in_sec = (unsigned long)r->age * c->attrs.aggr_interval / 1000000; + age_in_sec = div_u64((u64)r->age * c->attrs.aggr_interval, + USEC_PER_SEC); if (age_in_sec) age_in_log = min_t(int, ilog2(age_in_sec) + 1, DAMON_MAX_AGE_IN_LOG);