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...
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: 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@kernel.org Fixes: b9a6ac4e4ede ("mm/damon: adaptively adjust regions") Signed-off-by: SeongJae Park sj@kernel.org Cc: stable@vger.kernel.org [5.15+] Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
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@kernel.org 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