linux-ext4 - Re: [PATCH,RFC 4/7] ext4: remove page_skipped hackery in ext4_da

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Date:	Sat, 12 Feb 2011 20:36:58 -0500
From:	Josef Bacik <josef@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH,RFC 4/7] ext4: remove page_skipped hackery in
	ext4_da_writepages()

On Sat, Feb 12, 2011 at 07:15:54PM -0500, Theodore Ts'o wrote:
> Because the ext4 page writeback codepath had been prematurely calling
> clear_page_dirty_for_io(), if it turned out that a particular page
> couldn't be written out during a particular pass of
> write_cache_pages_da(), the page would have to get redirtied by
> calling redirty_pages_for_writeback().  Not only was this wasted work,
> but redirty_page_for_writeback() would increment wbc->pages_skipped to
> signal to writeback_sb_inodes() that buffers were locked, and that it
> should skip this inode until later.
> 
> Since this signal was incorrect in ext4's case --- which was caused by
> ext4's historically incorrect use of write_cache_pages() ---
> ext4_da_writepages() saved and restored wbc->skipped_pages to avoid
> confusing writeback_sb_inodes().
> 
> Now that we've fixed ext4 to call clear_page_dirty_for_io() right
> before initiating the page I/O, we can nuke the page_skipped
> save/restore hackery, and breathe a sigh of relief.
> 
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> ---
>  fs/ext4/inode.c |   10 ----------
>  1 files changed, 0 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 3eca465..6dfdc0e 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2900,7 +2900,6 @@ static int ext4_da_writepages(struct address_space *mapping,
>  	struct mpage_da_data mpd;
>  	struct inode *inode = mapping->host;
>  	int pages_written = 0;
> -	long pages_skipped;
>  	unsigned int max_pages;
>  	int range_cyclic, cycled = 1, io_done = 0;
>  	int needed_blocks, ret = 0;
> @@ -2986,8 +2985,6 @@ static int ext4_da_writepages(struct address_space *mapping,
>  	mpd.wbc = wbc;
>  	mpd.inode = mapping->host;
>  
> -	pages_skipped = wbc->pages_skipped;
> -
>  retry:
>  	if (wbc->sync_mode == WB_SYNC_ALL)
>  		tag_pages_for_writeback(mapping, index, end);
> @@ -3047,7 +3044,6 @@ retry:
>  			 * and try again
>  			 */
>  			jbd2_journal_force_commit_nested(sbi->s_journal);
> -			wbc->pages_skipped = pages_skipped;
>  			ret = 0;
>  		} else if (ret == MPAGE_DA_EXTENT_TAIL) {
>  			/*
> @@ -3055,7 +3051,6 @@ retry:
>  			 * rest of the pages
>  			 */
>  			pages_written += mpd.pages_written;
> -			wbc->pages_skipped = pages_skipped;
>  			ret = 0;
>  			io_done = 1;
>  		} else if (wbc->nr_to_write)
> @@ -3073,11 +3068,6 @@ retry:
>  		wbc->range_end  = mapping->writeback_index - 1;
>  		goto retry;
>  	}
> -	if (pages_skipped != wbc->pages_skipped)
> -		ext4_msg(inode->i_sb, KERN_CRIT,
> -			 "This should not happen leaving %s "
> -			 "with nr_to_write = %ld ret = %d",
> -			 __func__, wbc->nr_to_write, ret);
>  
>  	/* Update index */
>  	wbc->range_cyclic = range_cyclic;

Looks good.

Josef
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