Re: [PATCH 8/9] mm: Rearrange page flags

[Peter Xu <peterx@redhat.com>]

On Tue, Aug 15, 2023 at 04:26:44AM +0100, Matthew Wilcox (Oracle) wrote:
> Move PG_writeback into bottom byte so that it can use PG_waiters in a
> later patch.  Move PG_head into bottom byte as well to match with where
> 'order' is moving next.  PG_active and PG_workingset move into the second
> byte to make room for them.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
>  include/linux/page-flags.h | 24 +++++++++++-------------
>  1 file changed, 11 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> index aabf50dc71a3..6a0dd94b2460 100644
> --- a/include/linux/page-flags.h
> +++ b/include/linux/page-flags.h
> @@ -99,13 +99,15 @@
>   */
>  enum pageflags {
>  	PG_locked,		/* Page is locked. Don't touch. */
> +	PG_writeback,		/* Page is under writeback */
>  	PG_referenced,
>  	PG_uptodate,
>  	PG_dirty,
>  	PG_lru,
> +	PG_head,		/* Must be in bit 6 */

Could there be some explanation on "must be in bit 6" here?

Thanks,

-- 
Peter Xu