linux-kernel - Re: [PATCH 31/35] nfs: dont change wbc->nr_to_write in write

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Date:	Mon, 13 Dec 2010 16:01:44 -0500
From:	Trond Myklebust <Trond.Myklebust@...app.com>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
	Christoph Hellwig <hch@....de>,
	Dave Chinner <david@...morbit.com>,
	"Theodore Ts'o" <tytso@....edu>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mel Gorman <mel@....ul.ie>, Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Greg Thelen <gthelen@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	linux-mm <linux-mm@...ck.org>, linux-fsdevel@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 31/35] nfs: dont change wbc->nr_to_write in
 write_inode()

On Mon, 2010-12-13 at 22:47 +0800, Wu Fengguang wrote:
> plain text document attachment
> (writeback-nfs-commit-remove-nr_to_write.patch)
> It's introduced in commit 420e3646 ("NFS: Reduce the number of
> unnecessary COMMIT calls") and seems not necessary.
> 
> CC: Trond Myklebust <Trond.Myklebust@...app.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
>  fs/nfs/write.c |    9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> --- linux-next.orig/fs/nfs/write.c	2010-12-13 21:46:21.000000000 +0800
> +++ linux-next/fs/nfs/write.c	2010-12-13 21:46:22.000000000 +0800
> @@ -1557,15 +1557,8 @@ static int nfs_commit_unstable_pages(str
>  	}
>  
>  	ret = nfs_commit_inode(inode, flags);
> -	if (ret >= 0) {
> -		if (wbc->sync_mode == WB_SYNC_NONE) {
> -			if (ret < wbc->nr_to_write)
> -				wbc->nr_to_write -= ret;
> -			else
> -				wbc->nr_to_write = 0;
> -		}
> +	if (ret >= 0)
>  		return 0;
> -	}
>  out_mark_dirty:
>  	__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
>  	return ret;

It is there in order to tell the VM that it has succeeded in freeing up
a certain number of pages. Otherwise, we end up cycling forever in
writeback_sb_inodes() & friends with the latter not realising that they
have made progress.

Cheers
  Trond

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@...app.com
www.netapp.com

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