Re: [PATCH] mm/rmap: don't discard lazyfree THPs at PMD level

[Lance Yang <lance.yang@linux.dev>]

On 2026/10/10 10:08, Zi Yan wrote:
> __discard_anon_folio_pmd_locked() clears a lazyfree THP PMD before it knows
> whether the folio can be discarded, and restores it if the folio was
> redirtied or has extra references. A concurrent munmap() or
> MREMAP_DONTUNMAP skips the temporary none PMD and unlinks the VMA from its
> anon_vma, so the folio stays mapped after the anon_vma is freed and a later
> rmap walk uses the freed anon_vma.
> 
> Using an invalidated PMD instead of a cleared one requires additional arch
> code fixes. Instead, disable the PMD level discard of lazyfree THPs, as
> before commit 735ecdfaf4e8 ("mm/vmscan: avoid split lazyfree THP during
> shrink_folio_list()").
> 
> Fixes: 735ecdfaf4e8 ("mm/vmscan: avoid split lazyfree THP during shrink_folio_list()")
> Reported-by: Kyle Zeng <kylebot@openai.com>
> Closes: https://lore.kernel.org/r/20261009165214.40212-2-kylebot@openai.com
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Zi Yan <ziy@nvidia.com>
> ---

LGTM!

Reviewed-by: Lance Yang <lance.yang@linux.dev>