From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756180Ab1GJM7R (ORCPT ); Sun, 10 Jul 2011 08:59:17 -0400 Received: from wnohang.net ([178.79.154.173]:32964 "EHLO mail.wnohang.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756153Ab1GJM7P (ORCPT ); Sun, 10 Jul 2011 08:59:15 -0400 X-DKIM: Sendmail DKIM Filter v2.8.3 mail.wnohang.net 42873F0007 X-DKIM: Sendmail DKIM Filter v2.8.3 mail.wnohang.net 3B0B9F0003 Date: Sun, 10 Jul 2011 18:29:09 +0530 From: Raghavendra D Prabhu To: Wu Fengguang Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" Subject: Re: [TOME] Re: [PATCH 3/3] mm/readahead: Move the check for ra_pages after VM_SequentialReadHint() Message-ID: <20110710125909.GA4460@Xye> References: <323ddfc402a7f7b94f0cb02bba15acb2acca786f.1310239575.git.rprabhu@wnohang.net> <20110709205308.GC17463@localhost> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="jRHKVT23PllUwdXP" Content-Disposition: inline In-Reply-To: <20110709205308.GC17463@localhost> X-Operating-System: Arch linux x86_64 3.0.0-rc6-LYM X-Editor: VIM - Vi IMproved 7.3 User-Agent: Mutt/1.5.21 (2010-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --jRHKVT23PllUwdXP Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline * On Sat, Jul 09, 2011 at 01:53:08PM -0700, Wu Fengguang wrote: >On Sun, Jul 10, 2011 at 03:41:20AM +0800, Raghavendra D Prabhu wrote: >> page_cache_sync_readahead checks for ra->ra_pages again, so moving the check after VM_SequentialReadHint. > >NAK. This patch adds nothing but overheads. > >> --- a/mm/filemap.c >> +++ b/mm/filemap.c >> @@ -1566,8 +1566,6 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma, >> /* If we don't want any read-ahead, don't bother */ >> if (VM_RandomReadHint(vma)) >> return; >> - if (!ra->ra_pages) >> - return; >> if (VM_SequentialReadHint(vma)) { >> page_cache_sync_readahead(mapping, ra, file, offset, >> @@ -1575,6 +1573,9 @@ static void do_sync_mmap_readahead(struct vm_area_struct *vma, >> return; >> } >> + if (!ra->ra_pages) >> + return; >> + > >page_cache_sync_readahead() has the same > > if (!ra->ra_pages) > return; 1. Yes, I saw that and that is why I moved it after the condition, so that duplicate checks are not needed -- ie., if VM_SequentialReadHint is true, then (!ra->ra_pages) is checked twice otherwise. 2. Also, another thought, is the check needed at its original place (if not it can be removed), reasons being -- filesystems like tmpfs which have ra_pages set to 0 don't use filemap_fault in their VMA ops and also do_sync_mmap_readahead is called in a major page fault context. > >So the patch adds the call into page_cache_sync_readahead() just to return.. > >Thanks, >Fengguang > -------------------------- Raghavendra Prabhu GPG Id : 0xD72BE977 Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977 www: wnohang.net --jRHKVT23PllUwdXP Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.17 (GNU/Linux) iQEcBAEBAgAGBQJOGaIdAAoJEKYW3KHXK+l3q2AH/2JuXetggImM2X/RLTpPkaAJ /fz5doPJXng4Ix5xU0axJ/3BF9tPH5dyzZ2NEas4lnzD/fP9+w39bU6BxoExf6Fs 0ipoduw4bT0Mi1Rav/PcoePCebrsSNprYIVdKW1r+hVTULzu5VZt+27zUoD1xJI4 byj3uKvJCfcpwqPwYrLjnszMo+iZXiQ72RPwvxXHwx7YA0oJBgnp6d0dIhXhCnoc ikuvuU5Zl+HW5ehzUbQJNtHJj6lHkirCoRCbjsuBISyLtGRJnIo2OplMz3MfvAoB j5fmdE16PZEFk9/lpaTwlXJ4UdrLIWkfbq0cfkHrCee9fCZa+nxcI5KHCn1D3LU= =fTuG -----END PGP SIGNATURE----- --jRHKVT23PllUwdXP--