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 <jaeyeon.lee.dev@gmail.com>
Signed-off-by: SJ Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: SJ Park <sj@kernel.org>
Assisted-by: LLM

0 files changed, 0 insertions, 0 deletions