The patch titled
Subject: mm/damon/core: merge regions aggressively when max_nr_regions is unmet
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-damon-core-merge-regions-aggressively-when-max_nr_regions-is-unmet.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-merge-regions-aggressively-when-max_nr_regions-is-unmet.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@xxxxxxxxxx>
Subject: mm/damon/core: merge regions aggressively when max_nr_regions is unmet
Date: Mon, 24 Jun 2024 10:58:14 -0700
DAMON keeps the number of regions under max_nr_regions by skipping regions
split operations when doing so can make the number higher than the limit.
It works well for preventing violation of the limit. But, if somehow the
violation happens, it cannot recovery well depending on the situation. In
detail, if the real number of regions having different access pattern is
higher than the limit, the mechanism cannot reduce the number below the
limit. In such a case, the system could suffer from high monitoring
overhead of DAMON.
The violation can actually happen. For an example, the user could reduce
max_nr_regions while DAMON is running, to be lower than the current number
of regions. Fix the problem by repeating the merge operations with
increasing aggressiveness in kdamond_merge_regions() for the case, until
the limit is met.
Link: https://lkml.kernel.org/r/20240624175814.89611-1-sj@xxxxxxxxxx
Fixes: b9a6ac4e4ede ("mm/damon: adaptively adjust regions")
Signed-off-by: SeongJae Park <sj@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> [5.15+]
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/damon/core.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
--- a/mm/damon/core.c~mm-damon-core-merge-regions-aggressively-when-max_nr_regions-is-unmet
+++ a/mm/damon/core.c
@@ -1358,14 +1358,30 @@ static void damon_merge_regions_of(struc
* access frequencies are similar. This is for minimizing the monitoring
* overhead under the dynamically changeable access pattern. If a merge was
* unnecessarily made, later 'kdamond_split_regions()' will revert it.
+ *
+ * The total number of regions could be temporarily higher than the
+ * user-defined limit, max_nr_regions for some cases. For an example, the user
+ * updates max_nr_regions to a number that lower than the current number of
+ * regions while DAMON is running. Depending on the access pattern, it could
+ * take indefinitve time to reduce the number below the limit. For such a
+ * case, repeat merging until the limit is met while increasing @threshold and
+ * @sz_limit.
*/
static void kdamond_merge_regions(struct damon_ctx *c, unsigned int threshold,
unsigned long sz_limit)
{
struct damon_target *t;
+ unsigned int nr_regions;
- damon_for_each_target(t, c)
- damon_merge_regions_of(t, threshold, sz_limit);
+ do {
+ nr_regions = 0;
+ damon_for_each_target(t, c) {
+ damon_merge_regions_of(t, threshold, sz_limit);
+ nr_regions += damon_nr_regions(t);
+ }
+ threshold = max(1, threshold * 2);
+ sz_limit = max(1, sz_limit * 2);
+ } while (nr_regions > c->attrs.max_nr_regions);
}
/*
_
Patches currently in -mm which might be from sj@xxxxxxxxxx are
mm-damon-core-merge-regions-aggressively-when-max_nr_regions-is-unmet.patch
mm-damon-sysfs-schemes-add-target_nid-on-sysfs-schemes-fix.patch
docs-damon-document-damos_migrate_hotcold-fix.patch
mm-damon-core-implement-damos-quota-goals-online-commit-function.patch
mm-damon-core-implement-damon-context-commit-function.patch
mm-damon-sysfs-use-damon_commit_ctx.patch
mm-damon-sysfs-schemes-use-damos_commit_quota_goals.patch
mm-damon-sysfs-remove-unnecessary-online-tuning-handling-code.patch
mm-damon-sysfs-rename-damon_sysfs_set_targets-to-add_targets.patch
mm-damon-sysfs-schemes-remove-unnecessary-online-tuning-handling-code.patch
mm-damon-sysfs-schemes-rename-_set_schemesscheme_filtersquota_scoreschemes.patch
mm-damon-reclaim-use-damon_commit_ctx.patch
mm-damon-reclaim-remove-unnecessary-code-for-online-tuning.patch
mm-damon-lru_sort-use-damon_commit_ctx.patch
mm-damon-lru_sort-remove-unnecessary-online-tuning-handling-code.patch
docs-mm-damon-maintainer-profile-introduce-hackermail.patch
docs-mm-damon-maintainer-profile-document-damon-community-meetups.patch
