From: SeongJae Park Date: Tue, 16 Dec 2025 08:01:20 +0000 (-0800) Subject: mm/damon/core: implement max_nr_snapshots X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=84e425c68e6061751adecd2d328789e4f67eac1e;p=thirdparty%2Flinux.git mm/damon/core: implement max_nr_snapshots There are DAMOS use cases that require user-space centric control of its activation and deactivation. Having the control plane on the user-space, or using DAMOS as a way for monitoring results collection are such examples. DAMON parameters online commit, DAMOS quotas and watermarks can be useful for this purpose. However, those features work only at the sub-DAMON-snapshot level. In some use cases, the DAMON-snapshot level control is required. For example, in DAMOS-based monitoring results collection use case, the user online-installs a DAMOS scheme with DAMOS_STAT action, wait it be applied to whole regions of a single DAMON-snapshot, retrieves the stats and tried regions information, and online-uninstall the scheme. It is efficient to ensure the lifetime of the scheme as no more no less one snapshot consumption. To support such use cases, introduce a new DAMOS core API per-scheme parameter, namely max_nr_snapshots. As the name implies, it is the upper limit of nr_snapshots, which is a DAMOS stat that represents the number of DAMON-snapshots that the scheme has fully applied. If the limit is set with a non-zero value and nr_snapshots reaches or exceeds the limit, the scheme is deactivated. Link: https://lkml.kernel.org/r/20251216080128.42991-8-sj@kernel.org Signed-off-by: SeongJae Park Cc: Jonathan Corbet Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: "Masami Hiramatsu (Google)" Cc: Mathieu Desnoyers Cc: Michal Hocko Cc: Mike Rapoport Cc: Steven Rostedt Cc: Suren Baghdasaryan Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- diff --git a/include/linux/damon.h b/include/linux/damon.h index 43dfbfe2292f8..a67292a2f09dc 100644 --- a/include/linux/damon.h +++ b/include/linux/damon.h @@ -499,6 +499,7 @@ struct damos_migrate_dests { * @ops_filters: ops layer handling &struct damos_filter objects list. * @last_applied: Last @action applied ops-managing entity. * @stat: Statistics of this scheme. + * @max_nr_snapshots: Upper limit of nr_snapshots stat. * @list: List head for siblings. * * For each @apply_interval_us, DAMON finds regions which fit in the @@ -533,6 +534,9 @@ struct damos_migrate_dests { * finished. * * After applying the &action to each region, &stat is updated. + * + * If &max_nr_snapshots is set as non-zero and &stat.nr_snapshots be same to or + * greater than it, the scheme is deactivated. */ struct damos { struct damos_access_pattern pattern; @@ -567,6 +571,7 @@ struct damos { struct list_head ops_filters; void *last_applied; struct damos_stat stat; + unsigned long max_nr_snapshots; struct list_head list; }; diff --git a/mm/damon/core.c b/mm/damon/core.c index 9d5be7e9b8e01..344773f53f648 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -401,6 +401,7 @@ struct damos *damon_new_scheme(struct damos_access_pattern *pattern, INIT_LIST_HEAD(&scheme->core_filters); INIT_LIST_HEAD(&scheme->ops_filters); scheme->stat = (struct damos_stat){}; + scheme->max_nr_snapshots = 0; INIT_LIST_HEAD(&scheme->list); scheme->quota = *(damos_quota_init(quota)); @@ -1078,7 +1079,11 @@ static int damos_commit(struct damos *dst, struct damos *src) return err; err = damos_commit_filters(dst, src); - return err; + if (err) + return err; + + dst->max_nr_snapshots = src->max_nr_snapshots; + return 0; } static int damon_commit_schemes(struct damon_ctx *dst, struct damon_ctx *src) @@ -1984,6 +1989,10 @@ static void damon_do_apply_schemes(struct damon_ctx *c, if (damos_skip_charged_region(t, &r, s, c->min_sz_region)) continue; + if (s->max_nr_snapshots && + s->max_nr_snapshots <= s->stat.nr_snapshots) + continue; + if (damos_valid_target(c, t, r, s)) damos_apply_scheme(c, t, r, s);