linux-kernel - Re: [PATCH v2 19/28] iomap: Convert __iomap_zero

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Date:   Tue, 16 Nov 2021 18:24:24 -0800
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH v2 19/28] iomap: Convert __iomap_zero_iter to use a folio

On Mon, Nov 08, 2021 at 04:05:42AM +0000, Matthew Wilcox (Oracle) wrote:
> The zero iterator can work in folio-sized chunks instead of page-sized
> chunks.  This will save a lot of page cache lookups if the file is cached
> in multi-page folios.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>

hch's dax decoupling series notwithstanding,

Though TBH I am kinda wondering how the two of you plan to resolve those
kinds of differences -- I haven't looked at that series, though I think
this one's been waiting in the wings for longer?

Heck, I wonder how Matthew plans to merge all this given that it touches
mm, fs, block, and iomap...?

Reviewed-by: Darrick J. Wong <djwong@...nel.org>

--D

> ---
>  fs/iomap/buffered-io.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 64e54981b651..9c61d12028ca 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -881,17 +881,20 @@ EXPORT_SYMBOL_GPL(iomap_file_unshare);
>  
>  static s64 __iomap_zero_iter(struct iomap_iter *iter, loff_t pos, u64 length)
>  {
> +	struct folio *folio;
>  	struct page *page;
>  	int status;
> -	unsigned offset = offset_in_page(pos);
> -	unsigned bytes = min_t(u64, PAGE_SIZE - offset, length);
> +	size_t offset, bytes;
>  
> -	status = iomap_write_begin(iter, pos, bytes, &page);
> +	status = iomap_write_begin(iter, pos, length, &page);
>  	if (status)
>  		return status;
> +	folio = page_folio(page);
>  
> -	zero_user(page, offset, bytes);
> -	mark_page_accessed(page);
> +	offset = offset_in_folio(folio, pos);
> +	bytes = min_t(u64, folio_size(folio) - offset, length);
> +	folio_zero_range(folio, offset, bytes);
> +	folio_mark_accessed(folio);
>  
>  	return iomap_write_end(iter, pos, bytes, bytes, page);
>  }
> -- 
> 2.33.0
>