From 6e4930e33329eec80dd245f28b52202271f5fb28 Mon Sep 17 00:00:00 2001 From: Enze Li Date: Wed, 10 Dec 2025 13:25:08 +0800 Subject: [PATCH] mm/damon/core: fix wasteful CPU calls by skipping non-existent targets Currently, DAMON does not proactively clean up invalid monitoring targets during its runtime. When some monitored processes exit, DAMON continues to make the following unnecessary function calls, --damon_for_each_target-- --damon_for_each_region-- damon_do_apply_schemes damos_apply_scheme damon_va_apply_scheme damos_madvise damon_get_mm it is only in the damon_get_mm() function that it may finally discover the target no longer exists, which wastes CPU resources. A simple idea is to check for the existence of monitoring targets within the kdamond_need_stop() function and promptly clean up non-existent targets. However, SJ pointed out that this approach is problematic because the online commit logic incorrectly uses list indices to update the monitoring state. This can lead to data loss if the target list is changed concurrently. Meanwhile, SJ suggests checking for target existence at the damon_for_each_target level, and if a target does not exist, simply skip it and proceed to the next one. Link: https://lkml.kernel.org/r/20251210052508.264433-1-lienze@kylinos.cn Signed-off-by: Enze Li Suggested-by: SeongJae Park Reviewed-by: SeongJae Park Signed-off-by: Andrew Morton --- mm/damon/core.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/damon/core.c b/mm/damon/core.c index c852cac4f82e9..2379a07c2f877 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2299,6 +2299,9 @@ static void kdamond_apply_schemes(struct damon_ctx *c) 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_safe(r, next_r, t) damon_do_apply_schemes(c, t, r); } -- 2.47.3