+ mm-damon-core-use-time_in_range_open-for-damos-quota-window-start.patch added to mm-hotfixes-unstable branch

Andrew Morton
2026-04-01T03:33:02Z

The patch titled
Subject: mm/damon/core: use time_in_range_open() for damos quota window start
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-damon-core-use-time_in_range_open-for-damos-quota-window-start.patch

This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-damon-core-use-time_in_range_open-for-damos-quota-window-start.patch

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: SeongJae Park <sj@kernel.org>
Subject: mm/damon/core: use time_in_range_open() for damos quota window start
Date: Sun, 29 Mar 2026 08:23:05 -0700

damos_adjust_quota() uses time_after_eq() to show if it is time to start a
new quota charge window, comparing the current jiffies and the scheduled
next charge window start time. If it is, the next charge window start
time is updated and the new charge window starts.

The time check and next window start time update is skipped while the
scheme is deactivated by the watermarks. Let's suppose the deactivation
is kept more than LONG_MAX jiffies (assuming CONFIG_HZ of 250, more than
99 days in 32 bit systems and more than one billion years in 64 bit
systems), resulting in having the jiffies larger than the next charge
window start time + LONG_MAX. Then, the time_after_eq() call can return
false until another LONG_MAX jiffies are passed.

This means the scheme can continue working after being reactivated by the
watermarks. But, soon, the quota will be exceeded and the scheme will
again effectively stop working until the next charge window starts.
Because the current charge window is extended to up to LONG_MAX jiffies,
however, it will look like it stopped unexpectedly and indefinitely, from
the user's perspective.

Fix this by using !time_in_range_open() instead.

The issue was discovered [1] by sashiko.

Link: https://lkml.kernel.org/r/20260329152306.45796-1-sj@kernel.org
Link: https://lore.kernel.org/20260324040722.57944-1-sj@kernel.org [1]
Fixes: ee801b7dd782 ("mm/damon/schemes: activate schemes based on a watermarks mechanism")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 5.16.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

mm/damon/core.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/damon/core.c~mm-damon-core-use-time_in_range_open-for-damos-quota-window-start
+++ a/mm/damon/core.c
@@ -2291,7 +2291,8 @@ static void damos_adjust_quota(struct da
}

/* New charge window starts */
- if (time_after_eq(jiffies, quota->charged_from +
+ if (!time_in_range_open(jiffies, quota->charged_from,
+ quota->charged_from +
msecs_to_jiffies(quota->reset_interval))) {
if (quota->esz && quota->charged_sz >= quota->esz)
s->stat.qt_exceeds++;
_

Patches currently in -mm which might be from sj@kernel.org are

mm-damon-sysfs-dealloc-repeat_call_control-if-damon_call-fails.patch
mm-damon-core-fix-damon_call-vs-kdamond_fn-exit-race.patch
mm-damon-core-fix-damos_walk-vs-kdamond_fn-exit-race.patch
mm-damon-core-validate-damos_quota_goal-nid-for-node_mem_usedfree_bp.patch
mm-damon-core-validate-damos_quota_goal-nid-for-node_memcg_usedfree_bp.patch
mm-damon-core-use-time_in_range_open-for-damos-quota-window-start.patch