Re: [PATCH v1] mm/huge_memory: improve split_huge_page_to_list_to_order() return value documentation

[John Hubbard]

On 4/22/24 12:31 PM, David Hildenbrand wrote:
> On 19.04.24 02:15, John Hubbard wrote:
> > On 4/18/24 8:18 AM, David Hildenbrand wrote:
..
> > >     *
> > >     * Returns 0 if the huge page was split successfully.
> > >     *
> > > - * Returns -EBUSY if @page's folio is pinned, or if the anon_vma disappeared
> > > - * from under us.
> > > + * Returns -EAGAIN if the folio has unexpected reference (e.g., GUP).
> >
> > ...or if the folio was removed from the page cache before this routine
> > got a chance to lock it, right? (See the "fail:" path.)
>
> Right, that is sneaky. Let me extend to cover that case as well.
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 824eff9211db8..a7406267323ed 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2975,7 +2975,8 @@ bool can_split_folio(struct folio *folio, int *pextra_pins)
>    *
>    * Returns 0 if the huge page was split successfully.
>    *
> - * Returns -EAGAIN if the folio has unexpected reference (e.g., GUP).
> + * Returns -EAGAIN if the folio has unexpected reference (e.g., GUP) or if
> + * the folio was concurrently removed from the page cache.

Looks good,

Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>

thanks,
--
John Hubbard
NVIDIA