From: SJ Park <sj@kernel.org>
To: Sasha Levin <sashal@kernel.org>
Cc: SJ Park <sj@kernel.org>,
	stable@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 6.18.y 3/5] mm/damon: rename DAMON_MIN_REGION to DAMON_MIN_REGION_SZ
Date: Wed, 30 Sep 2026 02:12:44 -0700
Message-ID: <20260930091245.43609-1-sj@kernel.org>
In-Reply-To: <20260930000354.2861391-3-sashal@kernel.org>
References: 
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Hello Sasha,

On Tue, 29 Sep 2026 20:03:52 -0400 Sasha Levin <sashal@kernel.org> wrote:

> From: SeongJae Park <sj@kernel.org>
> 
> [ Upstream commit dfb1b0c9dc0d61e422905640e1e7334b3cf6f384 ]
> 
> The macro is for the default minimum size of each DAMON region.  There was
> a case that a reader was confused if it is the minimum number of total
> DAMON regions, which is set on damon_attrs->min_nr_regions.  Make the name
> more explicit.
> 
> Link: https://lkml.kernel.org/r/20260117175256.82826-8-sj@kernel.org
> Signed-off-by: SeongJae Park <sj@kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> 
> Stable adaptation for b3723b596b548c837a766aae3553c14a7b15af2b:

Thank you for this work for making DAMON fixes in stable kernels!  However,
this looks wrong backport to me.  Please read below for details.

[...]
> @@ -1763,15 +1765,14 @@ static bool damos_skip_charged_region(struct damon_target *t,
>  		if (quota->charge_addr_from && r->ar.start <
>  				quota->charge_addr_from) {
>  			sz_to_skip = ALIGN_DOWN(quota->charge_addr_from -
> -					r->ar.start, min_sz_region);
> +					r->ar.start, min_region_sz);
>  			if (!sz_to_skip) {
> -				if (damon_sz_region(r) <= min_sz_region)
> +				if (damon_sz_region(r) <= min_region_sz)
>  					return true;
> -				sz_to_skip = min_sz_region;
> +				sz_to_skip = min_region_sz;
>  			}
>  			damon_split_region_at(t, r, sz_to_skip);
> -			r = damon_next_region(r);
> -			*rp = r;
> +			return true;

In mainline, the above change was introduced with commit 1745ccbd2907d
("mm/damon/core: do non-safe region walk on kdamond_apply_schemes()").  This
patch is trying to backport dfb1b0c9dc0d ("mm/damon: rename DAMON_MIN_REGION to
DAMON_MIN_REGION_SZ"), so the above change shouldn't be in this patch.  Also,
seems not all changes in commit 1745ccbd2907d ("mm/damon/core: do non-safe
region walk on kdamond_apply_schemes()") are added in this patch.
Particualrly, seems this patch is not doing damon_for_each_region_safe() ->
damon_for_each_region() change, which can introduce another subtle bug.

Could we use my manual backport [1] instead of this series?

[1] https://lore.kernel.org/20260929174456.9251-2-sj@kernel.org


Thanks,
SJ

[...]