The patch titled Subject: mm/damon/core: prevent unnecessary overflow in damos_set_effective_quota() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-damon-core-prevent-unnecessary-overflow-in-damos_set_effective_quota.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Quanmin Yan yanquanmin1@huawei.com Subject: mm/damon/core: prevent unnecessary overflow in damos_set_effective_quota() Date: Thu, 21 Aug 2025 20:55:55 +0800
On 32-bit systems, the throughput calculation in damos_set_effective_quota() is prone to unnecessary multiplication overflow. Using mult_frac() to fix it.
Andrew Paniakin also recently found and privately reported this issue, on 64 bit systems. This can also happen on 64-bit systems, once the charged size exceeds ~17 TiB. On systems running for long time in production, this issue can actually happen.
More specifically, when a DAMOS scheme having the time quota run for longtime, throughput calculation can overflow and set esz too small. As a result, speed of the scheme get unexpectedly slow.
Link: https://lkml.kernel.org/r/20250821125555.3020951-1-yanquanmin1@huawei.com Fixes: 1cd243030059 ("mm/damon/schemes: implement time quota") Signed-off-by: Quanmin Yan yanquanmin1@huawei.com Reported-by: Andrew Paniakin apanyaki@amazon.com Reviewed-by: SeongJae Park sj@kernel.org Cc: Kefeng Wang wangkefeng.wang@huawei.com Cc: ze zuo zuoze1@huawei.com Cc: stable@vger.kernel.org [5.16+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
mm/damon/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/damon/core.c~mm-damon-core-prevent-unnecessary-overflow-in-damos_set_effective_quota +++ a/mm/damon/core.c @@ -2073,8 +2073,8 @@ static void damos_set_effective_quota(st
if (quota->ms) { if (quota->total_charged_ns) - throughput = quota->total_charged_sz * 1000000 / - quota->total_charged_ns; + throughput = mult_frac(quota->total_charged_sz, 1000000, + quota->total_charged_ns); else throughput = PAGE_SIZE * 1024; esz = min(throughput * quota->ms, esz); _
Patches currently in -mm which might be from yanquanmin1@huawei.com are
mm-damon-core-prevent-unnecessary-overflow-in-damos_set_effective_quota.patch