linux-kernel - Re: [PATCH v3 15/25] iomap: Allow iomap_write_begin() to be called with the full length

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Date:   Thu, 16 Dec 2021 13:43:16 -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
Subject: Re: [PATCH v3 15/25] iomap: Allow iomap_write_begin() to be called
 with the full length

On Thu, Dec 16, 2021 at 09:07:05PM +0000, Matthew Wilcox (Oracle) wrote:
> In the future, we want write_begin to know the entire length of the
> write so that it can choose to allocate large folios.  Pass the full
> length in from __iomap_zero_iter() and limit it where necessary.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>

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

--D

> ---
>  fs/iomap/buffered-io.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 8d7a67655b60..b1ded5204d1c 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -619,6 +619,9 @@ static int iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
>  	if (fatal_signal_pending(current))
>  		return -EINTR;
>  
> +	if (!mapping_large_folio_support(iter->inode->i_mapping))
> +		len = min_t(size_t, len, PAGE_SIZE - offset_in_page(pos));
> +
>  	if (page_ops && page_ops->page_prepare) {
>  		status = page_ops->page_prepare(iter->inode, pos, len);
>  		if (status)
> @@ -632,6 +635,8 @@ static int iomap_write_begin(const struct iomap_iter *iter, loff_t pos,
>  		goto out_no_page;
>  	}
>  	folio = page_folio(page);
> +	if (pos + len > folio_pos(folio) + folio_size(folio))
> +		len = folio_pos(folio) + folio_size(folio) - pos;
>  
>  	if (srcmap->type == IOMAP_INLINE)
>  		status = iomap_write_begin_inline(iter, page);
> @@ -891,11 +896,13 @@ static s64 __iomap_zero_iter(struct iomap_iter *iter, loff_t pos, u64 length)
>  	struct page *page;
>  	int status;
>  	unsigned offset = offset_in_page(pos);
> -	unsigned bytes = min_t(u64, PAGE_SIZE - offset, length);
> +	unsigned bytes = min_t(u64, UINT_MAX, length);
>  
>  	status = iomap_write_begin(iter, pos, bytes, &page);
>  	if (status)
>  		return status;
> +	if (bytes > PAGE_SIZE - offset)
> +		bytes = PAGE_SIZE - offset;
>  
>  	zero_user(page, offset, bytes);
>  	mark_page_accessed(page);
> -- 
> 2.33.0
>