From: Josef Bacik <josef@redhat.com>
Subject: Re: [PATCH,RFC 5/7] ext4: don't lock the next page in
	write_cache_pages if not needed
Date: Sat, 12 Feb 2011 20:38:07 -0500
Message-ID: <20110213013806.GH19533@dhcp231-156.rdu.redhat.com>
References: <1297556157-21559-1-git-send-email-tytso@mit.edu> <1297556157-21559-6-git-send-email-tytso@mit.edu>
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Cc: Ext4 Developers List <linux-ext4@vger.kernel.org>
To: "Theodore Ts'o" <tytso@mit.edu>
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In-Reply-To: <1297556157-21559-6-git-send-email-tytso@mit.edu>
Sender: linux-ext4-owner@vger.kernel.org

On Sat, Feb 12, 2011 at 07:15:55PM -0500, Theodore Ts'o wrote:
> If we have accumulated a contiguous region of memory to be written
> out, and the next page can added to this region, don't bother locking
> (and then unlocking the page) before writing out the memory.  In the
> unlikely event that the next page was being written back by some other
> CPU, we can also skip waiting that page to finish writeback.
> 
> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> ---
>  fs/ext4/inode.c |   27 ++++++++++-----------------
>  1 files changed, 10 insertions(+), 17 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 6dfdc0e..2ac64e3 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2761,6 +2761,16 @@ static int write_cache_pages_da(struct address_space *mapping,
>  
>  			*done_index = page->index + 1;
>  
> +			/*
> +			 * If we can't merge this page, and we have
> +			 * accumulated an contiguous region, write it
> +			 */
> +			if ((mpd->next_page != page->index) &&
> +			    (mpd->next_page != mpd->first_page)) {
> +				mpage_da_map_and_submit(mpd);
> +				goto ret_extent_tail;
> +			}
> +
>  			lock_page(page);
>  
>  			/*
> @@ -2784,25 +2794,8 @@ static int write_cache_pages_da(struct address_space *mapping,
>  
>  			BUG_ON(PageWriteback(page));
>  
> -			/*
> -			 * Can we merge this page to current extent?
> -			 */
>  			if (mpd->next_page != page->index) {
>  				/*
> -				 * Nope, we can't. So, we map
> -				 * non-allocated blocks and start IO
> -				 * on them
> -				 */
> -				if (mpd->next_page != mpd->first_page) {
> -					mpage_da_map_and_submit(mpd);
> -					/*
> -					 * skip rest of the page in the page_vec
> -					 */
> -					unlock_page(page);
> -					goto ret_extent_tail;
> -				}
> -
> -				/*
>  				 * Start next extent of pages and blocks
>  				 */
>  				mpd->first_page = page->index;

Looks good.

Josef