+ mm-damon-core-handle-zero-schemes-apply-interval.patch added to mm-hotfixes-unstable branch

+ mm-damon-core-handle-zero-schemes-apply-interval.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/damon/core: handle zero schemes apply interval
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-damon-core-handle-zero-schemes-apply-interval.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-handle-zero-schemes-apply-interval.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: handle zero schemes apply interval
Date: Thu, 31 Oct 2024 11:37:57 -0700

DAMON's logics to determine if this is the time to apply damos schemes
assumes next_apply_sis is always set larger than current
passed_sample_intervals.  And therefore assume continuously incrementing
passed_sample_intervals will make it reaches to the next_apply_sis in
future.  The logic hence does apply the scheme and update next_apply_sis
only if passed_sample_intervals is same to next_apply_sis.

If Schemes apply interval is set as zero, however, next_apply_sis is set
same to current passed_sample_intervals, respectively.  And
passed_sample_intervals is incremented before doing the next_apply_sis
check.  Hence, next_apply_sis becomes larger than next_apply_sis, and the
logic says it is not the time to apply schemes and update next_apply_sis. 
In other words, DAMON stops applying schemes until passed_sample_intervals
overflows.

Based on the documents and the common sense, a reasonable behavior for
such inputs would be applying the schemes for every sampling interval. 
Handle the case by removing the assumption.

Link: https://lkml.kernel.org/r/20241031183757.49610-3-sj@kernel.org
Fixes: 42f994b71404 ("mm/damon/core: implement scheme-specific apply interval")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org>	[6.7.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/damon/core.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/mm/damon/core.c~mm-damon-core-handle-zero-schemes-apply-interval
+++ a/mm/damon/core.c
@@ -1412,7 +1412,7 @@ static void damon_do_apply_schemes(struc
 	damon_for_each_scheme(s, c) {
 		struct damos_quota *quota = &s->quota;
 
-		if (c->passed_sample_intervals != s->next_apply_sis)
+		if (c->passed_sample_intervals < s->next_apply_sis)
 			continue;
 
 		if (!s->wmarks.activated)
@@ -1622,7 +1622,7 @@ static void kdamond_apply_schemes(struct
 	bool has_schemes_to_apply = false;
 
 	damon_for_each_scheme(s, c) {
-		if (c->passed_sample_intervals != s->next_apply_sis)
+		if (c->passed_sample_intervals < s->next_apply_sis)
 			continue;
 
 		if (!s->wmarks.activated)
@@ -1642,9 +1642,9 @@ static void kdamond_apply_schemes(struct
 	}
 
 	damon_for_each_scheme(s, c) {
-		if (c->passed_sample_intervals != s->next_apply_sis)
+		if (c->passed_sample_intervals < s->next_apply_sis)
 			continue;
-		s->next_apply_sis +=
+		s->next_apply_sis = c->passed_sample_intervals +
 			(s->apply_interval_us ? s->apply_interval_us :
 			 c->attrs.aggr_interval) / sample_interval;
 	}
_

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

mm-damon-core-handle-zero-aggregationops_update-intervals.patch
mm-damon-core-handle-zero-schemes-apply-interval.patch
selftests-damon-huge_count_read_write-remove-unnecessary-debugging-message.patch
selftests-damon-_debugfs_common-hide-expected-error-message-from-test_write_result.patch
selftests-damon-debugfs_duplicate_context_creation-hide-errors-from-expected-file-write-failures.patch
mm-damon-kconfig-update-dbgfs_kunit-prompt-copy-for-sysfs_kunit.patch
mm-damon-tests-dbgfs-kunit-fix-the-header-double-inclusion-guarding-ifdef-comment.patch