linux-kernel - [PATCH 3/3] mm/damon/core: do damos walking in entire regions granularity

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Message-Id: <20250210182737.134994-4-sj@kernel.org>
Date: Mon, 10 Feb 2025 10:27:36 -0800
From: SeongJae Park <sj@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: SeongJae Park <sj@...nel.org>,
	damon@...ts.linux.dev,
	kernel-team@...a.com,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH 3/3] mm/damon/core: do damos walking in entire regions granularity

damos_walk_control can be installed while DAMOS is walking the regions.
This means the walk callback function invocations can be started from a
region at the middle of the regions list.  This makes it hard to be used
reliably.  Particularly, DAMOS tried regions update for collecting
monitoring results gets problematic results.  Increase the
walk_control_lock critical section to do walking in entire regions
granularity.

Fixes: bf0eaba0ff9c ("mm/damon/core: implement damos_walk()")
Signed-off-by: SeongJae Park <sj@...nel.org>
---
 mm/damon/core.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 4b865b2558d9..c3d9b96b786a 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -1456,11 +1456,10 @@ static void damos_walk_call_walk(struct damon_ctx *ctx, struct damon_target *t,
 	if (s->walk_completed)
 		return;
 
-	mutex_lock(&ctx->walk_control_lock);
 	control = ctx->walk_control;
-	mutex_unlock(&ctx->walk_control_lock);
 	if (!control)
 		return;
+
 	control->walk_fn(control->data, ctx, t, r, s, sz_filter_passed);
 }
 
@@ -1480,9 +1479,7 @@ static void damos_walk_complete(struct damon_ctx *ctx, struct damos *s)
 	struct damos *siter;
 	struct damos_walk_control *control;
 
-	mutex_lock(&ctx->walk_control_lock);
 	control = ctx->walk_control;
-	mutex_unlock(&ctx->walk_control_lock);
 	if (!control)
 		return;
 
@@ -1496,9 +1493,7 @@ static void damos_walk_complete(struct damon_ctx *ctx, struct damos *s)
 		siter->walk_completed = false;
 
 	complete(&control->completion);
-	mutex_lock(&ctx->walk_control_lock);
 	ctx->walk_control = NULL;
-	mutex_unlock(&ctx->walk_control_lock);
 }
 
 /*
@@ -1845,6 +1840,7 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
 	if (!has_schemes_to_apply)
 		return;
 
+	mutex_lock(&c->walk_control_lock);
 	damon_for_each_target(t, c) {
 		damon_for_each_region_safe(r, next_r, t)
 			damon_do_apply_schemes(c, t, r);
@@ -1859,6 +1855,7 @@ static void kdamond_apply_schemes(struct damon_ctx *c)
 			 c->attrs.aggr_interval) / sample_interval;
 		s->last_applied = NULL;
 	}
+	mutex_unlock(&c->walk_control_lock);
 }
 
 /*
-- 
2.39.5