[PATCH] mm/damon/core: reduce kernel stack usage

[PATCH] mm/damon/core: reduce kernel stack usage

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

The main thread function has recently grown to the point of
exceeding stack frame size warning limits in some configurations.
This is what I hit on s390 with clang and CONFIG_KASAN:

mm/damon/core.c:3440:31: error: stack frame size (1352) exceeds limit (1280) in 'kdamond_fn' [-Werror,-Wframe-larger-than]
 3440 | static int kdamond_fn(struct damon_ctx *ctx)

The largest stack usage here is inside of the kdamond_tune_intervals(),
so by marking that one as noinline_for_stack, the functions individually
stay below the warning limit, though kdamond_fn() itself still uses
hundreds of kilobytes for some reason.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 mm/damon/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/damon/core.c b/mm/damon/core.c
index 265d51ade25b..69f38c48ac08 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2002,7 +2002,7 @@ static unsigned long damon_get_intervals_adaptation_bp(struct damon_ctx *c)
 	return adaptation_bp;
 }
 
-static void kdamond_tune_intervals(struct damon_ctx *c)
+static noinline_for_stack void kdamond_tune_intervals(struct damon_ctx *c)
 {
 	unsigned long adaptation_bp;
 	struct damon_attrs new_attrs;
-- 
2.39.5

Re: [PATCH] mm/damon/core: reduce kernel stack usage

[SeongJae Park]

On Thu, 11 Jun 2026 14:56:57 +0200 Arnd Bergmann <arnd@kernel.org> wrote:

> From: Arnd Bergmann <arnd@arndb.de>
> 
> The main thread function has recently grown to the point of
> exceeding stack frame size warning limits in some configurations.
> This is what I hit on s390 with clang and CONFIG_KASAN:
> 
> mm/damon/core.c:3440:31: error: stack frame size (1352) exceeds limit (1280) in 'kdamond_fn' [-Werror,-Wframe-larger-than]
>  3440 | static int kdamond_fn(struct damon_ctx *ctx)
> 
> The largest stack usage here is inside of the kdamond_tune_intervals(),
> so by marking that one as noinline_for_stack, the functions individually
> stay below the warning limit, though kdamond_fn() itself still uses
> hundreds of kilobytes for some reason.

Thank you for this fix, Arnd!  I will also take a look in kdamond_fn() to see
if there are more things to reduce.

> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Reviewed-by: SeongJae Park <sj@kernel.org>

Should we add Fixes: and Cc: stable@ too?  This function was introduced by
commit f04b0fedbe71 ("mm/damon/core: implement intervals auto-tuning") which
was merged into 6.15.


Thanks,
SJ

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