diff options
| author |   Quanmin Yan <yanquanmin1@huawei.com> | 2025-08-21 20:55:55 +0800 |
|---|---|---|
| committer |   Andrew Morton <akpm@linux-foundation.org> | 2025-08-27 22:45:43 -0700 |
| commit | 9f68eabab9d9aaa764a8d234c4170119e6518102 (patch) | |
| tree | a0391b80733fdeb6741dff9bbf7791d7448fc481 | |
| parent | kexec: add KEXEC_FILE_NO_CMA as a legal flag (diff) | |
| download | wireguard-linux-9f68eabab9d9aaa764a8d234c4170119e6518102.tar.xz wireguard-linux-9f68eabab9d9aaa764a8d234c4170119e6518102.zip | |
mm/damon/core: prevent unnecessary overflow in damos_set_effective_quota()
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>
| -rw-r--r-- | mm/damon/core.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/mm/damon/core.c b/mm/damon/core.c index 70eff5cbe6ee..106ee8b0f2d5 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2073,8 +2073,8 @@ static void damos_set_effective_quota(struct damos_quota *quota) 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); |