Re: [RFC PATCH v1.2 5/8] mm/damon/vaddr: respect folio end for DAMOS_MIGRATE_{HOT,COLD}

[sashiko-bot@kernel.org]

> For applying DAMOS_MIGRATE_{HOT,COLD} actions to a region, DAMON virtual
> address space operation set (vaddr) calls walk_page_range[_vma]() for
> the region.  The pmd walk entry function, namely
> damon_va_migrate_pmd_entry(), collects folios of addresses of the region
> in the pmd.  It starts from the walking address and advances the address
> by the size of the folio of the address until it goes out of the pmd or
> the region.
> 
> Let's suppose it is for the first pmd of the region, and the region
> start address is in the middle of a large folio.  Also, the next folios
> are small.  Then, some of the next folios could be skipped.  Fix the
> issue by advancing the address to exactly the start address of the next
> folio.
> 
> The user impact is that DAMOS action is applied to less than expected
> amount of memory.  Given the best effort nature of DAMON, it is no big
> problem, but it is clearly a bug that is better to be fixed.
> 
> The issue was discovered [1] by Sashiko.
> 
> [1] https://lore.kernel.org/20260514015053.149396-1-sj@kernel.org
> 
> Fixes: 09efc56a3b1c ("mm/damon/vaddr: consistently use only pmd_entry for damos_migrate")
> Cc: <stable@vger.kernel.org> # 6.19.x
> Signed-off-by: SJ Park <sj@kernel.org>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260831140254.72004-1-sj@kernel.org?part=5