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

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

On Wed, Mar 05, 2025 at 07:05:28AM -0700, 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>

Seems fine to me, so
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  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(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index f28ca5cb5bd8..c7f4cafda705 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -206,9 +206,7 @@ xfs_buf_free(
>  	if (!xfs_buftarg_is_mem(bp->b_target) && size >= PAGE_SIZE)
>  		mm_account_reclaimed_pages(howmany(size, PAGE_SHIFT));
>  
> -	if (xfs_buftarg_is_mem(bp->b_target))
> -		xmbuf_unmap_page(bp);
> -	else if (is_vmalloc_addr(bp->b_addr))
> +	if (is_vmalloc_addr(bp->b_addr))
>  		vfree(bp->b_addr);
>  	else if (bp->b_flags & _XBF_KMEM)
>  		kfree(bp->b_addr);
> @@ -275,7 +273,7 @@ xfs_buf_alloc_backing_mem(
>  	struct folio	*folio;
>  
>  	if (xfs_buftarg_is_mem(bp->b_target))
> -		return xmbuf_map_page(bp);
> +		return xmbuf_map_backing_mem(bp);
>  
>  	/* Assure zeroed buffer for non-read cases. */
>  	if (!(flags & XBF_READ))
> diff --git a/fs/xfs/xfs_buf_mem.c b/fs/xfs/xfs_buf_mem.c
> index b207754d2ee0..b4ffd80b7cb6 100644
> --- a/fs/xfs/xfs_buf_mem.c
> +++ b/fs/xfs/xfs_buf_mem.c
> @@ -74,7 +74,7 @@ xmbuf_alloc(
>  
>  	/*
>  	 * We don't want to bother with kmapping data during repair, so don't
> -	 * allow highmem pages to back this mapping.
> +	 * allow highmem folios to back this mapping.
>  	 */
>  	mapping_set_gfp_mask(inode->i_mapping, GFP_KERNEL);
>  
> @@ -127,14 +127,13 @@ xmbuf_free(
>  	kfree(btp);
>  }
>  
> -/* Directly map a shmem page into the buffer cache. */
> +/* Directly map a shmem folio into the buffer cache. */
>  int
> -xmbuf_map_page(
> +xmbuf_map_backing_mem(
>  	struct xfs_buf		*bp)
>  {
>  	struct inode		*inode = file_inode(bp->b_target->bt_file);
>  	struct folio		*folio = NULL;
> -	struct page		*page;
>  	loff_t                  pos = BBTOB(xfs_buf_daddr(bp));
>  	int			error;
>  
> @@ -159,30 +158,17 @@ xmbuf_map_page(
>  		return -EIO;
>  	}
>  
> -	page = folio_file_page(folio, pos >> PAGE_SHIFT);
> -
>  	/*
> -	 * Mark the page dirty so that it won't be reclaimed once we drop the
> -	 * (potentially last) reference in xmbuf_unmap_page.
> +	 * Mark the folio dirty so that it won't be reclaimed once we drop the
> +	 * (potentially last) reference in xfs_buf_free.
>  	 */
> -	set_page_dirty(page);
> -	unlock_page(page);
> +	folio_set_dirty(folio);
> +	folio_unlock(folio);
>  
> -	bp->b_addr = page_address(page);
> +	bp->b_addr = folio_address(folio);

If tmpfs gives us a large folio, don't we need to add offset_in_folio to
b_addr?  Or does this just work and xfs/801 (aka force the use of
hugepages on tmpfs) passes with no complaints?

--D

>  	return 0;
>  }
>  
> -/* Unmap a shmem page that was mapped into the buffer cache. */
> -void
> -xmbuf_unmap_page(
> -	struct xfs_buf		*bp)
> -{
> -	ASSERT(xfs_buftarg_is_mem(bp->b_target));
> -
> -	put_page(virt_to_page(bp->b_addr));
> -	bp->b_addr = NULL;
> -}
> -
>  /* Is this a valid daddr within the buftarg? */
>  bool
>  xmbuf_verify_daddr(
> @@ -196,7 +182,7 @@ xmbuf_verify_daddr(
>  	return daddr < (inode->i_sb->s_maxbytes >> BBSHIFT);
>  }
>  
> -/* Discard the page backing this buffer. */
> +/* Discard the folio backing this buffer. */
>  static void
>  xmbuf_stale(
>  	struct xfs_buf		*bp)
> @@ -211,7 +197,7 @@ xmbuf_stale(
>  }
>  
>  /*
> - * Finalize a buffer -- discard the backing page if it's stale, or run the
> + * Finalize a buffer -- discard the backing folio if it's stale, or run the
>   * write verifier to detect problems.
>   */
>  int
> 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);
> +
>  #endif /* __XFS_BUF_MEM_H__ */
> -- 
> 2.45.2
> 
>