Re: [PATCH 11/12] xfs: cleanup mapping tmpfs folios into the buffer cache

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Feb 26, 2025 at 07:51:39AM -0800, Christoph Hellwig wrote:
> Directly assign b_addr based on the tmpfs folios without a detour
> through pages, reuse the folio_put path used for non-tmpfs buffers
> and replace all references to pages in comments with folios.
> 
> Partially based on a patch from Dave Chinner <dchinner@redhat.com>.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  fs/xfs/xfs_buf.c     |  6 ++----
>  fs/xfs/xfs_buf_mem.c | 34 ++++++++++------------------------
>  fs/xfs/xfs_buf_mem.h |  6 ++----
>  3 files changed, 14 insertions(+), 32 deletions(-)
> 

<snip>

> diff --git a/fs/xfs/xfs_buf_mem.h b/fs/xfs/xfs_buf_mem.h
> index eed4a7b63232..67d525cc1513 100644
> --- a/fs/xfs/xfs_buf_mem.h
> +++ b/fs/xfs/xfs_buf_mem.h
> @@ -19,16 +19,14 @@ int xmbuf_alloc(struct xfs_mount *mp, const char *descr,
>  		struct xfs_buftarg **btpp);
>  void xmbuf_free(struct xfs_buftarg *btp);
>  
> -int xmbuf_map_page(struct xfs_buf *bp);
> -void xmbuf_unmap_page(struct xfs_buf *bp);
>  bool xmbuf_verify_daddr(struct xfs_buftarg *btp, xfs_daddr_t daddr);
>  void xmbuf_trans_bdetach(struct xfs_trans *tp, struct xfs_buf *bp);
>  int xmbuf_finalize(struct xfs_buf *bp);
>  #else
>  # define xfs_buftarg_is_mem(...)	(false)
> -# define xmbuf_map_page(...)		(-ENOMEM)
> -# define xmbuf_unmap_page(...)		((void)0)
>  # define xmbuf_verify_daddr(...)	(false)
>  #endif /* CONFIG_XFS_MEMORY_BUFS */
>  
> +int xmbuf_map_backing_mem(struct xfs_buf *bp);

Does this actually work if CONFIG_XFS_MEMORY_BUFS=n ?  I guess the
compiler will see:

	if (false)
		return xmbuf_map_backing_mem(bp);

and optimize it out, right?  But these subtleties make my eyes twitch.

--D

> +
>  #endif /* __XFS_BUF_MEM_H__ */
> -- 
> 2.45.2
> 
>