Re: [RESEND PATCH] mm/damon/tests/core-kunit: add test for unconditionally skipping the last region

[Liew Rui Yan]

Hi SJ,

Just a reminder, I think you might have missed the question I asked.

On Sun, 20 Sep 2026 03:09:10 +0800 Liew Rui Yan <aethernet65535@xxxxxxxxx> wrote:

> On Sat, 19 Sep 2026 09:07:25 -0700 SJ Park <sj@xxxxxxxxxx> wrote:
> 
> > On Sat, 19 Sep 2026 16:01:58 +0800 Liew Rui Yan <aethernet65535@xxxxxxxxx> wrote:
> > 
> > > Commit 50585192bc2e ("mm/damon/schemes: skip already charged targets and
> > > regions") introduced a minor issue that causes the last region to be
> > > skipped before it is processed.
> > > 
> > > Example:
> > > 
> > >     1. Target has 2 regions: R1 (0-100 bytes) and R2 (100-200 bytes).
> > >     2. Quota is configured to process only 100 bytes per window.
> > >     3. Window 1: Processes R1 (0-100).  Quota is full.  charge_{target,
> > >        addr}_from is saved at (Target, 100).
> > >     4. Window 2: The loop reaches R2.  Because R2 is
> > >        damon_last_region(t), the old code unconditionally returns true,
> > >        skipping R2 entirely and resetting the charge_{target,addr}_from.
> > > 
> > >     Result: R2 is permanently skipped even though it has never been
> > >     processed.
> > > 
> > > Add a test to prevent this regression in the future.
> > > 
> > > Signed-off-by: Liew Rui Yan <aethernet65535@xxxxxxxxx>
> > 
> > Other than a trivial style that I commented below,
> > 
> > Reviewed-by: SJ Park <sj@xxxxxxxxxx>
> > 
> > [...]
> > > +static void damon_test_last_region_quota_reset(struct kunit *test)
> > > +{
> > [...]
> > > +	t = damon_new_target();
> > > +	if (!t) {
> > > +		kunit_skip(test, "target alloc fail");
> > > +	}
> > 
> > Let's drop braces for single line, as suggested [1] in coding-style.
> 
> I will change this in next revision.
> 
> By the way, Sashiko reported an issue [1]: min_region_sz is not
> power-of-2.  While this do not cause any real issue in this test,
> non-power-of-2's min_region_sz is not legal.  Should min_region_sz
> initial value set to power-of-2 value (e.g., PAGE_SIZE) in the next
> revision?
> 

[...]

> [1] https://lore.kernel.org/damon/20260919081239.8A3D91F000FF@xxxxxxxxxxxxxxx

[...]

Best regards,
Rui Yan