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Sun, 22 Mar 2026 22:36:32 +0100 (CET) From: Josh Law To: sj@kernel.org, akpm@linux-foundation.org Cc: damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Josh Law Subject: [PATCH v2 1/2] mm/damon/core: optimize kdamond_apply_schemes() by inverting scheme and region loops Date: Sun, 22 Mar 2026 21:36:30 +0000 Message-Id: <20260322213631.259212-2-objecting@objecting.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260322213631.259212-1-objecting@objecting.org> References: <20260322213631.259212-1-objecting@objecting.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-ZohoMailClient: External X-Rspamd-Queue-Id: 5668510000A X-Rspamd-Server: rspam07 X-Stat-Signature: obsticcg9szzdj48ju5kctgr47a6gits X-Rspam-User: X-HE-Tag: 1774215405-31739 X-HE-Meta: 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 0jHh9CEV CgfbRoUXgbnh6EMJOmX4h/hHv46bQq8Aezg9hjDyGtoeUZa2AN0s1CGamKlB9uSCD8m0j8GijVgUE7fk2If0mI+OsuhVOB5tM9nTaFdHPtsGRICANqijGxMjbs6zO7MqJs1seRGMEgG1398+KZhK8D7z/yoKUtUBz9c3ex2IUaTHLboVmNVUoRUy6tk8feQqw02hnxqJzFVqbo1KIivTWlayYOCSsbxoctpimdd6yR7cffkwLpHXqiLJp/IzU7Jf+r/lwGXQiRHT67EuPW86mNZB1tfOyVOvKWCo2Qbd73EyVFEVGl9eFqgjeyZ+KtLDGBk1wL0FZvM6hx3Vl7HKz79iH2zgiE2yt7pkri9wwO1bhHkFCl1Qf2St28CymyC7DO38Rh3whdY/Xolg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Currently, kdamond_apply_schemes() iterates over all targets, then over all regions, and finally calls damon_do_apply_schemes() which iterates over all schemes. This nested structure causes scheme-level invariants (such as time intervals, activation status, and quota limits) to be evaluated inside the innermost loop for every single region. If a scheme is inactive, has not reached its apply interval, or has already fulfilled its quota (quota->charged_sz >= quota->esz), the kernel still needlessly iterates through thousands of regions only to repeatedly evaluate these same scheme-level conditions and continue. This patch inlines damon_do_apply_schemes() into kdamond_apply_schemes() and inverts the loop ordering. It now iterates over schemes on the outside, and targets/regions on the inside. This allows the code to evaluate scheme-level limits once per scheme. If a scheme's quota is met or it is inactive, we completely bypass the O(Targets * Regions) inner loop for that scheme. This drastically reduces unnecessary branching, cache thrashing, and CPU overhead in the kdamond hot path. Signed-off-by: Josh Law --- mm/damon/core.c | 72 +++++++++++++++++++++---------------------------- 1 file changed, 30 insertions(+), 42 deletions(-) diff --git a/mm/damon/core.c b/mm/damon/core.c index c884bb31c9b8..dece0da079c8 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2112,40 +2112,6 @@ static void damos_apply_scheme(struct damon_ctx *c, struct damon_target *t, damos_update_stat(s, sz, sz_applied, sz_ops_filter_passed); } -static void damon_do_apply_schemes(struct damon_ctx *c, - struct damon_target *t, - struct damon_region *r) -{ - struct damos *s; - - damon_for_each_scheme(s, c) { - struct damos_quota *quota = &s->quota; - - if (time_before(c->passed_sample_intervals, s->next_apply_sis)) - continue; - - if (!s->wmarks.activated) - continue; - - /* Check the quota */ - if (quota->esz && quota->charged_sz >= quota->esz) - continue; - - if (damos_skip_charged_region(t, r, s, c->min_region_sz)) - continue; - - if (s->max_nr_snapshots && - s->max_nr_snapshots <= s->stat.nr_snapshots) - continue; - - if (damos_valid_target(c, r, s)) - damos_apply_scheme(c, t, r, s); - - if (damon_is_last_region(r, t)) - s->stat.nr_snapshots++; - } -} - /* * damon_feed_loop_next_input() - get next input to achieve a target score. * @last_input The last input. @@ -2494,17 +2460,39 @@ static void kdamond_apply_schemes(struct damon_ctx *c) return; mutex_lock(&c->walk_control_lock); - damon_for_each_target(t, c) { - if (c->ops.target_valid && c->ops.target_valid(t) == false) - continue; - - damon_for_each_region(r, t) - damon_do_apply_schemes(c, t, r); - } - damon_for_each_scheme(s, c) { + struct damos_quota *quota = &s->quota; + if (time_before(c->passed_sample_intervals, s->next_apply_sis)) continue; + + if (!s->wmarks.activated) + continue; + + damon_for_each_target(t, c) { + if (c->ops.target_valid && c->ops.target_valid(t) == false) + continue; + + damon_for_each_region(r, t) { + /* Check the quota */ + if (quota->esz && quota->charged_sz >= quota->esz) + goto next_scheme; + + if (s->max_nr_snapshots && + s->max_nr_snapshots <= s->stat.nr_snapshots) + goto next_scheme; + + if (damos_skip_charged_region(t, r, s, c->min_region_sz)) + continue; + + if (damos_valid_target(c, r, s)) + damos_apply_scheme(c, t, r, s); + + if (damon_is_last_region(r, t)) + s->stat.nr_snapshots++; + } + } +next_scheme: damos_walk_complete(c, s); damos_set_next_apply_sis(s, c); s->last_applied = NULL; -- 2.34.1