Date: Fri, 20 Aug 2010 08:33:08 +0800
From: Wu Fengguang <fengguang.wu@gmail.com>
To: Jeff Layton <jlayton@redhat.com>
Cc: Trond Myklebust <trond.myklebust@fys.uio.no>,
        Christoph Hellwig <hch@infradead.org>, linux-nfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: why are WB_SYNC_NONE COMMITs being done with FLUSH_SYNC set ?
Message-ID: <20100820003308.GA30548@localhost>
References: <20100819101525.076831ad@barsoom.rdu.redhat.com>
 <20100819143710.GA4752@infradead.org>
 <1282229905.6199.19.camel@heimdal.trondhjem.org>
 <20100819151618.5f769dc9@tlielax.poochiereds.net>
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In-Reply-To: <20100819151618.5f769dc9@tlielax.poochiereds.net>
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> Here's a lightly tested patch that turns the check for the two flags
> into a check for WB_SYNC_NONE. It seems to do the right thing, but I
> don't have a clear testcase for it. Does this look reasonable?
 
Yes, I don't see any problems.

> ------------------[snip]------------------------
> 
> NFS: don't use FLUSH_SYNC on WB_SYNC_NONE COMMIT calls
> 
> WB_SYNC_NONE is supposed to mean "don't wait on anything". That should
> also include not waiting for COMMIT calls to complete.
> 
> WB_SYNC_NONE is also implied when wbc->nonblocking or
> wbc->for_background are set, so we can replace those checks in
> nfs_commit_unstable_pages with a check for WB_SYNC_NONE.
>
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  fs/nfs/write.c |   10 +++++-----
>  1 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/nfs/write.c b/fs/nfs/write.c
> index 874972d..35bd7d0 100644
> --- a/fs/nfs/write.c
> +++ b/fs/nfs/write.c
> @@ -1436,12 +1436,12 @@ static int nfs_commit_unstable_pages(struct inode *inode, struct writeback_contr
>  	/* Don't commit yet if this is a non-blocking flush and there are
>  	 * lots of outstanding writes for this mapping.
>  	 */
> -	if (wbc->sync_mode == WB_SYNC_NONE &&
> -	    nfsi->ncommit <= (nfsi->npages >> 1))
> -		goto out_mark_dirty;
> -
> -	if (wbc->nonblocking || wbc->for_background)
> +	if (wbc->sync_mode == WB_SYNC_NONE) {
> +		if (nfsi->ncommit <= (nfsi->npages >> 1))
> +			goto out_mark_dirty;
>  		flags = 0;
> +	}
> +

nitpick: I'd slightly prefer an one-line change

-       if (wbc->nonblocking || wbc->for_background)
+       if (wbc->sync_mode == WB_SYNC_NONE)
                flags = 0;

That way the patch will look more obvious and "git blame" friendly,
and the original "Don't commit.." comment will best match its code.

Reviewed-by: Wu Fengguang <fengguang.wu@intel.com>

Thanks,
Fengguang