Re: [PATCH v4 10/17] mm/huge_memory: move the racy refcount check into unmap_folio()

[Zi Yan]

On Mon Sep 7, 2026 at 2:12 PM EDT, Kairui Song via B4 Relay wrote:
> From: Kairui Song <kasong@xxxxxxxxxxx>
>
> The check only exists to avoid the expensive PMD-splitting unmap of a
> folio that cannot be split anyway.  Move it from __folio_split() into
> unmap_folio(), right before the PMD split, so both the anon and file
> split helpers get the early check without repeating it.
>
> unmap_folio() now returns -EAGAIN if the check fails and the split
> helpers propagate the error.  folio_split_unmapped() drops its own
> copy of the check: it works on already unmapped folios and the
> definitive folio_ref_freeze() in __folio_freeze_split_anon() still
> catches unexpected references.
>
> Signed-off-by: Kairui Song <kasong@xxxxxxxxxxx>
> ---
>  mm/huge_memory.c | 29 +++++++++++++----------------
>  1 file changed, 13 insertions(+), 16 deletions(-)
>
LGTM.

Reviewed-by: Zi Yan <ziy@xxxxxxxxxx>


-- 
Best Regards,
Yan, Zi