Re: [PATCH 7.2 v2 05/12] mm/khugepaged: remove READ_ONLY_THP_FOR_FS check in hugepage_pmd_enabled()

Matthew Wilcox
2026-04-13T20:34:09Z

On Mon, Apr 13, 2026 at 03:20:23PM -0400, Zi Yan wrote:
> After READ_ONLY_THP_FOR_FS Kconfig is removed, this check becomes dead
> code.
>
> This changes hugepage_pmd_enabled() semantics. Previously, with
> READ_ONLY_THP_FOR_FS enabled, hugepage_pmd_enabled() returned true whenever
> /sys/kernel/mm/transparent_hugepage/enabled was set to "always" or
> "madvise".
>
> After this change, hugepage_pmd_enabled() is governed only by the anon and
> shmem PMD THP controls. As a result, khugepaged collapse for file-backed
> folios no longer runs unconditionally under the top-level THP setting, and
> now depends on the anon/shmem PMD configuration.

This seems like it'll turn off khugepaged too easily. I would have
thought we'd want:

- if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) &&
- hugepage_global_enabled())
+ if (hugepage_global_enabled())
return true;

... or maybe this whole thing could be simplified?