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

[Liew Rui Yan]

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://docs.kernel.org/process/coding-style.html#placing-braces-and-spaces
> 

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

Best regards,
Rui Yan