linux-kernel - Re: [PATCH 05/13] writeback: rework the loop termination condition in write_cache

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Date: Mon, 5 Feb 2024 10:32:10 -0500
From: Brian Foster <bfoster@...hat.com>
To: Christoph Hellwig <hch@....de>
Cc: linux-mm@...ck.org, Matthew Wilcox <willy@...radead.org>,
	Jan Kara <jack@...e.com>, David Howells <dhowells@...hat.com>,
	Christian Brauner <brauner@...nel.org>,
	"Darrick J. Wong" <djwong@...nel.org>, linux-xfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/13] writeback: rework the loop termination condition
 in write_cache_pages

On Sat, Feb 03, 2024 at 08:11:39AM +0100, Christoph Hellwig wrote:
> Rework the way we deal with the cleanup after the writepage call.
> 
> First handle the magic AOP_WRITEPAGE_ACTIVATE separately from real error
> returns to get it out of the way of the actual error handling path.
> 
> The split the handling on intgrity vs non-integrity branches first,
> and return early using a goto for the non-ingegrity early loop condition
> to remove the need for the done and done_index local variables, and for
> assigning the error to ret when we can just return error directly.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  mm/page-writeback.c | 84 ++++++++++++++++++---------------------------
>  1 file changed, 33 insertions(+), 51 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index c7c494526bc650..88b2c4c111c01b 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
..
> @@ -2524,14 +2505,15 @@ int write_cache_pages(struct address_space *mapping,
>  	 * of the file if we are called again, which can only happen due to
>  	 * -ENOMEM from the file system.
>  	 */
> -	if (wbc->range_cyclic) {
> -		if (done)
> -			mapping->writeback_index = done_index;
> -		else
> -			mapping->writeback_index = 0;
> -	}
> -
> +	if (wbc->range_cyclic)
> +		mapping->writeback_index = 0;
>  	return ret;
> +
> +done:
> +	folio_batch_release(&fbatch);
> +	if (wbc->range_cyclic)
> +		mapping->writeback_index = folio->index + folio_nr_pages(folio);

Shouldn't this release the batch after we're done accessing folio? With
that addressed:

Reviewed-by: Brian Foster <bfoster@...hat.com>

> +	return error;
>  }
>  EXPORT_SYMBOL(write_cache_pages);
>  
> -- 
> 2.39.2
> 
>