From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754950AbYLADTp (ORCPT ); Sun, 30 Nov 2008 22:19:45 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752963AbYLADTf (ORCPT ); Sun, 30 Nov 2008 22:19:35 -0500 Received: from mga14.intel.com ([143.182.124.37]:26352 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752922AbYLADTe (ORCPT ); Sun, 30 Nov 2008 22:19:34 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.33,692,1220252400"; d="scan'208";a="84691709" Date: Mon, 1 Dec 2008 11:19:22 +0800 From: Wu Fengguang To: Andrew Morton Cc: linux-nfs@vger.kernel.org, Trond Myklebust , LKML , "stable@kernel.org" Subject: [PATCH] nfs: remove redundant tests on reading new pages Message-ID: <20081201031922.GA31077@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org aops->readpages() and its NFS helper readpage_async_filler() will only be called to do readahead I/O for newly allocated pages. So it's not necessary to test for the always 0 dirty/uptodate page flags. The removal of nfs_wb_page() call also fixes a readahead bug: the NFS readahead has been synchronous since 2.6.23, because that call will clear PG_readahead, which is the reminder for asynchronous readahead. More background: the PG_readahead page flag is shared with PG_reclaim, one for read path and the other for write path. clear_page_dirty_for_io() unconditionally clears PG_readahead to prevent possible readahead residuals, assuming itself to be always called in the write path. However, NFS is one and the only exception in that it _always_ calls clear_page_dirty_for_io() in the read path, i.e. for readpages()/readpage(). Cc: Trond Myklebust Signed-off-by: Wu Fengguang --- fs/nfs/read.c | 6 ------ 1 file changed, 6 deletions(-) This bug was found when playing with my readahead tracing module posted at http://lkml.org/lkml/2008/11/27/373 and confirmed to work. The NFS readahead traces are now [ 59.972526] readahead-initial0(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=0+25, ra=0+60-30, async=0) = 60 [ 59.992734] readahead-subsequent(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=30+20, ra=60+30-30, async=1) = 30 [ 60.030900] readahead-subsequent(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=60+15, ra=90+30-30, async=1) = 30 [ 60.031687] readahead-subsequent(pid=3646(dd), dev=00:0f(0:f), ino=293189(1G), req=90+10, ra=120+30-30, async=1) = 30 The async field was always 0 before this patch. --- linux-2.6.orig/fs/nfs/read.c +++ linux-2.6/fs/nfs/read.c @@ -533,12 +533,6 @@ readpage_async_filler(void *data, struct unsigned int len; int error; - error = nfs_wb_page(inode, page); - if (error) - goto out_unlock; - if (PageUptodate(page)) - goto out_unlock; - len = nfs_page_length(page); if (len == 0) return nfs_return_empty_page(page);