Re: [PATCH 02/12] xfs: add a fast path to xfs_buf_zero when b_addr is set

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

On Wed, Feb 26, 2025 at 07:51:30AM -0800, Christoph Hellwig wrote:
> No need to walk the page list if bp->b_addr is valid.  That also means
> b_offset doesn't need to be taken into account in the unmapped loop as
> b_offset is only set for kmem backed buffers which are always mapped.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

That's much clearer!
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

--D

> ---
>  fs/xfs/xfs_buf.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> index 15bb790359f8..9e0c64511936 100644
> --- a/fs/xfs/xfs_buf.c
> +++ b/fs/xfs/xfs_buf.c
> @@ -1688,13 +1688,18 @@ xfs_buf_zero(
>  {
>  	size_t			bend;
>  
> +	if (bp->b_addr) {
> +		memset(bp->b_addr + boff, 0, bsize);
> +		return;
> +	}
> +
>  	bend = boff + bsize;
>  	while (boff < bend) {
>  		struct page	*page;
>  		int		page_index, page_offset, csize;
>  
> -		page_index = (boff + bp->b_offset) >> PAGE_SHIFT;
> -		page_offset = (boff + bp->b_offset) & ~PAGE_MASK;
> +		page_index = boff >> PAGE_SHIFT;
> +		page_offset = boff & ~PAGE_MASK;
>  		page = bp->b_pages[page_index];
>  		csize = min_t(size_t, PAGE_SIZE - page_offset,
>  				      BBTOB(bp->b_length) - boff);
> -- 
> 2.45.2
> 
>