The patch titled Subject: mm/damon/core: set quota->charged_from to jiffies at first charge window has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-damon-core-set-quota-charged_from-to-jiffies-at-first-charge-window.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: Sang-Heon Jeon ekffu200098@gmail.com Subject: mm/damon/core: set quota->charged_from to jiffies at first charge window Date: Wed, 20 Aug 2025 00:01:23 +0900

Kernel initializes "jiffies" timer as 5 minutes below zero, as shown in include/linux/jiffies.h

/* * Have the 32 bit jiffies value wrap 5 minutes after boot * so jiffies wrap bugs show up earlier. */ #define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))

And they cast unsigned value to signed to cover wraparound

#define time_after_eq(a,b) \ (typecheck(unsigned long, a) && \ typecheck(unsigned long, b) && \ ((long)((a) - (b)) >= 0))

In 64bit systems, these might not be a problem because wrapround occurs 300 million years after the boot, assuming HZ value is 1000.

With same assuming, In 32bit system, wraparound occurs 5 minutues after the initial boot and every 49 days after the first wraparound. And about 25 days after first wraparound, it continues quota charging window up to next 25 days.

Example 1: initial boot jiffies=0xFFFB6C20, charged_from+interval=0x000003E8 time_after_eq(jiffies, charged_from+interval)=(long)0xFFFB6838; In signed values, it is considered negative so it is false.

Example 2: after about 25 days first wraparound jiffies=0x800004E8, charged_from+interval=0x000003E8 time_after_eq(jiffies, charged_from+interval)=(long)0x80000100; In signed values, it is considered negative so it is false

So, change quota->charged_from to jiffies at damos_adjust_quota() when it is consider first charge window.

In theory; but almost impossible; quota->total_charged_sz and qutoa->charged_from should be both zero even if it is not in first charge window. But It will only delay one reset_interval, So it is not big problem.

Link: https://lkml.kernel.org/r/20250819150123.1532458-1-ekffu200098@gmail.com Fixes: 2b8a248d5873 ("mm/damon/schemes: implement size quota for schemes application speed control") [5.16] Signed-off-by: Sang-Heon Jeon ekffu200098@gmail.com Reviewed-by: SeongJae Park sj@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/damon/core.c | 4 ++++ 1 file changed, 4 insertions(+)

--- a/mm/damon/core.c~mm-damon-core-set-quota-charged_from-to-jiffies-at-first-charge-window +++ a/mm/damon/core.c @@ -2111,6 +2111,10 @@ static void damos_adjust_quota(struct da if (!quota->ms && !quota->sz && list_empty(&quota->goals)) return;

+ /* First charge window */ + if (!quota->total_charged_sz && !quota->charged_from) + quota->charged_from = jiffies; + /* New charge window starts */ if (time_after_eq(jiffies, quota->charged_from + msecs_to_jiffies(quota->reset_interval))) { _

Patches currently in -mm which might be from ekffu200098@gmail.com are

mm-damon-core-fix-commit_ops_filters-by-using-correct-nth-function.patch selftests-damon-fix-selftests-by-installing-drgn-related-script.patch mm-damon-core-fix-damos_commit_filter-not-changing-allow.patch mm-damon-core-set-quota-charged_from-to-jiffies-at-first-charge-window.patch mm-damon-update-expired-description-of-damos_action.patch docs-mm-damon-design-fix-typo-s-sz_trtied-sz_tried.patch selftests-damon-test-no-op-commit-broke-damon-status.patch selftests-damon-test-no-op-commit-broke-damon-status-fix.patch mm-damon-tests-core-kunit-add-damos_commit_filter-test.patch