[PATCH] mm: Fix compile error when CONFIG_SHMEM is not set

[Linus Torvalds]

On Tue, 3 Jun 2025 at 10:26, Steven Rostedt <rostedt at goodmis.org> wrote:
>
>  config DRM_TTM
>         tristate
> -       depends on DRM && MMU
> +       depends on DRM && MMU && SHMEM

Yeah, except I think you should just make it be

          depends on DRM && SHMEM

because SHMEM already depends on MMU.

That said, our docs already say that if you disable SHMEM, it gets
replaced by RAMFS, so maybe just having a ramfs version is the
RightThing(tm).

I don't think such a ramfs version should just return 0 - much less an
error. I think it should always redirty the page.

IOW, I think the "ramfs" version should look something like

        folio_mark_dirty(folio);
        if (wbc->for_reclaim)
                return AOP_WRITEPAGE_ACTIVATE;  /* Return with folio locked */
        folio_unlock(folio);
        return 0;

which is what shmem does for the "page is locked" case.

            Linus