linux-kernel - Re: [PATCH 6/6] NFS: return -EAGAIN when skipped commit in nfs_commit_unstable

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Message-ID: <1303183747.5417.11.camel@lade.trondhjem.org>
Date:	Mon, 18 Apr 2011 23:29:07 -0400
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>,
	Mel Gorman <mel@...ux.vnet.ibm.com>,
	Dave Chinner <david@...morbit.com>,
	Itaru Kitayama <kitayama@...bb4u.ne.jp>,
	Minchan Kim <minchan.kim@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [PATCH 6/6] NFS: return -EAGAIN when skipped commit in
 nfs_commit_unstable_pages()

On Tue, 2011-04-19 at 11:00 +0800, Wu Fengguang wrote:
> plain text document attachment (nfs-fix-write_inode-retval.patch)
> It's probably not sane to return success while redirtying the inode at
> the same time in ->write_inode().
> 
> CC: Trond Myklebust <Trond.Myklebust@...app.com>
> Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> ---
>  fs/nfs/write.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- linux-next.orig/fs/nfs/write.c	2011-04-19 10:18:16.000000000 +0800
> +++ linux-next/fs/nfs/write.c	2011-04-19 10:18:32.000000000 +0800
> @@ -1519,7 +1519,7 @@ static int nfs_commit_unstable_pages(str
>  {
>  	struct nfs_inode *nfsi = NFS_I(inode);
>  	int flags = FLUSH_SYNC;
> -	int ret = 0;
> +	int ret = -EAGAIN;
>  
>  	if (wbc->sync_mode == WB_SYNC_NONE) {
>  		/* Don't commit yet if this is a non-blocking flush and there
> 
> 

Hi Fengguang,

I don't understand the purpose of this patch...

Currently, the value of 'ret' only affects the case where the commit
exits early due to this being a non-blocking flush where we have not yet
written back enough pages to make it worth our while to send a commit.

In essence, this really only matters for the cases where someone calls
'write_inode_now' (not used by anybody calling into the NFS client) and
'sync_inode', which is only called by nfs_wb_all (with sync_mode =
WB_SYNC_ALL).

So can you please elaborate on the possible use cases for this change?

Cheers
  Trond
-- 
Trond Myklebust
Linux NFS client maintainer

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

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