linux-kernel - Re: [PATCH 03/11] writeback: Factor should_writeback_folio() out of write_cache

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Message-ID: <20231215141631.aooan5rby6fwfdof@quack3>
Date: Fri, 15 Dec 2023 15:16:31 +0100
From: Jan Kara <jack@...e.cz>
To: Christoph Hellwig <hch@....de>
Cc: linux-mm@...ck.org, "Matthew Wilcox (Oracle)" <willy@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jan Kara <jack@...e.com>, David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 03/11] writeback: Factor should_writeback_folio() out of
 write_cache_pages()

On Thu 14-12-23 14:25:36, Christoph Hellwig wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> 
> Reduce write_cache_pages() by about 30 lines; much of it is commentary,
> but it all bundles nicely into an obvious function.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Signed-off-by: Christoph Hellwig <hch@....de>

I like this! Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  mm/page-writeback.c | 59 ++++++++++++++++++++++++---------------------
>  1 file changed, 32 insertions(+), 27 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 5d33e7b468e2cc..5a3df8665ff4f9 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2394,6 +2394,36 @@ static void writeback_get_batch(struct address_space *mapping,
>  			&wbc->fbatch);
>  }
>  
> +static bool should_writeback_folio(struct address_space *mapping,
> +		struct writeback_control *wbc, struct folio *folio)
> +{
> +	/*
> +	 * Folio truncated or invalidated. We can freely skip it then,
> +	 * even for data integrity operations: the folio has disappeared
> +	 * concurrently, so there could be no real expectation of this
> +	 * data integrity operation even if there is now a new, dirty
> +	 * folio at the same pagecache index.
> +	 */
> +	if (unlikely(folio->mapping != mapping))
> +		return false;
> +
> +	/* Did somebody write it for us? */
> +	if (!folio_test_dirty(folio))
> +		return false;
> +
> +	if (folio_test_writeback(folio)) {
> +		if (wbc->sync_mode == WB_SYNC_NONE)
> +			return false;
> +		folio_wait_writeback(folio);
> +	}
> +
> +	BUG_ON(folio_test_writeback(folio));
> +	if (!folio_clear_dirty_for_io(folio))
> +		return false;
> +
> +	return true;
> +}
> +
>  /**
>   * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
>   * @mapping: address space structure to write
> @@ -2462,38 +2492,13 @@ int write_cache_pages(struct address_space *mapping,
>  			wbc->done_index = folio->index;
>  
>  			folio_lock(folio);
> -
> -			/*
> -			 * Page truncated or invalidated. We can freely skip it
> -			 * then, even for data integrity operations: the page
> -			 * has disappeared concurrently, so there could be no
> -			 * real expectation of this data integrity operation
> -			 * even if there is now a new, dirty page at the same
> -			 * pagecache address.
> -			 */
> -			if (unlikely(folio->mapping != mapping)) {
> -continue_unlock:
> +			if (!should_writeback_folio(mapping, wbc, folio)) {
>  				folio_unlock(folio);
>  				continue;
>  			}
>  
> -			if (!folio_test_dirty(folio)) {
> -				/* someone wrote it for us */
> -				goto continue_unlock;
> -			}
> -
> -			if (folio_test_writeback(folio)) {
> -				if (wbc->sync_mode != WB_SYNC_NONE)
> -					folio_wait_writeback(folio);
> -				else
> -					goto continue_unlock;
> -			}
> -
> -			BUG_ON(folio_test_writeback(folio));
> -			if (!folio_clear_dirty_for_io(folio))
> -				goto continue_unlock;
> -
>  			trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
> +
>  			error = writepage(folio, wbc, data);
>  			nr = folio_nr_pages(folio);
>  			if (unlikely(error)) {
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR