Re: [PATCH v2] mm/damon/tests/core-kunit: add test for unconditionally skipping the last region

[Liew Rui Yan]

On Fri, 25 Sep 2026 02:02:38 -0700 SJ Park <sj@xxxxxxxxxx> wrote:

> On Fri, 25 Sep 2026 12:53:35 +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.
> 
> The bug is fixed by commit b3723b596b54 ("mm/damon/core: fix unconditionally
> skip last region"), which is merged into the mainline for 7.3-rc5.  Could you
> update the commit message to mention the fix, rather than the original bug?
> The fix commit already has a quite good description of the bug, so I don't
> think we need to duplicate it here.
> 
> Other than that, looks good to me.

Okay, I will change the commit message in the next revision.

    Commit b3723b596b54 ("mm/damon/core: fix unconditionally skip last
    region") fixed a minor bug.

    Add a KUnit test case to cover this behavior and prevent regressions
    in the future.

[...]

Best regards,
Rui Yan