Re: [PATCH 3/5] mm/damon/core: receive addr_unit on damon_set_region_biggest_system_ram_default()

[SeongJae Park <sj@kernel.org>]

On Tue, 10 Mar 2026 22:29:24 -0700 SeongJae Park <sj@kernel.org> wrote:

> damon_find_biggest_system_ram() was not supporting addr_unit in the
> past.  Hence, its caller, damon_set_region_biggest_system_ram_default(),
> was also not supporting addr_unit.  The previous commit has updated the
> inner function to support addr_unit.  There is no more reason to not
> support addr_unit on damon_set_region_biggest_system_ram_default().
> Rather, it makes unnecessary inconsistency on support of addr_unit.
> Update it to receive addr_unit and handle it inside.
> 
> Signed-off-by: SeongJae Park <sj@kernel.org>
> ---
>  include/linux/damon.h | 1 +
>  mm/damon/core.c       | 7 ++++---
>  mm/damon/lru_sort.c   | 1 +
>  mm/damon/reclaim.c    | 1 +
>  mm/damon/stat.c       | 2 +-
>  5 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/damon.h b/include/linux/damon.h
> index 1130c2f9a92f4..3a441fbca170d 100644
> --- a/include/linux/damon.h
> +++ b/include/linux/damon.h
> @@ -988,6 +988,7 @@ int damos_walk(struct damon_ctx *ctx, struct damos_walk_control *control);
>  
>  int damon_set_region_biggest_system_ram_default(struct damon_target *t,
>  				unsigned long *start, unsigned long *end,
> +				unsigned long addr_unit,
>  				unsigned long min_region_sz);
>  
>  #endif	/* CONFIG_DAMON */
> diff --git a/mm/damon/core.c b/mm/damon/core.c
> index aee61bf991baa..d4f86c20b4f48 100644
[...]
> --- a/mm/damon/core.c
> +++ b/mm/damon/core.c
[...]
> @@ -3123,12 +3124,12 @@ int damon_set_region_biggest_system_ram_default(struct damon_target *t,
>  		return -EINVAL;
>  
>  	if (!*start && !*end &&
> -		!damon_find_biggest_system_ram(start, end, 1))
> +			!damon_find_biggest_system_ram(start, end, addr_unit))
>  		return -EINVAL;
>  
>  	addr_range.start = *start;
>  	addr_range.end = *end;
> -	return damon_set_regions(t, &addr_range, 1, min_region_sz);
> +	return damon_set_regions(t, &addr_range, addr_unit, min_region_sz);

The above line is unnecessarily and wrongly changing the third argument.  It is
the number of ranges that passed by the second argument, never meant to be the
addr_unit.

A similar bug [1] was found by an AI review, and I found this patch also has a
similar bug.

Andrew, could you please add below attaching fixup?

[1] https://lore.kernel.org/20260313234026.48872-1-sj@kernel.org


Thanks,
SJ

[...]
=== >8 ===
From 0d00bb5ca76502aef4a6a97b0855e33435147269 Mon Sep 17 00:00:00 2001
From: SeongJae Park <sj@kernel.org>
Date: Fri, 13 Mar 2026 16:49:08 -0700
Subject: [PATCH] mm/damon/core: fix wrong damon_set_regions() argument

The third argument is the length of the second parameter.  But addr_unit
is wrongly being passed.  Fix it.

Signed-off-by: SeongJae Park <sj@kernel.org>
---
 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 d4f86c20b4f48..f9854aedc42d1 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -3129,7 +3129,7 @@ int damon_set_region_biggest_system_ram_default(struct damon_target *t,
 
 	addr_range.start = *start;
 	addr_range.end = *end;
-	return damon_set_regions(t, &addr_range, addr_unit, min_region_sz);
+	return damon_set_regions(t, &addr_range, 1, min_region_sz);
 }
 
 /*
-- 
2.47.3