From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754694Ab1GJP7M (ORCPT ); Sun, 10 Jul 2011 11:59:12 -0400 Received: from mga02.intel.com ([134.134.136.20]:20773 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753360Ab1GJP7I (ORCPT ); Sun, 10 Jul 2011 11:59:08 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.65,509,1304319600"; d="scan'208";a="25938642" Date: Sun, 10 Jul 2011 08:59:06 -0700 From: Wu Fengguang To: Raghavendra D Prabhu 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: <20110710155906.GB7432@localhost> References: <323ddfc402a7f7b94f0cb02bba15acb2acca786f.1310239575.git.rprabhu@wnohang.net> <20110709205308.GC17463@localhost> <20110710125909.GA4460@Xye> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110710125909.GA4460@Xye> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 10, 2011 at 08:59:09PM +0800, Raghavendra D Prabhu wrote: > * 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. Ok, I see. > 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 Good point. tmpfs is using shmem_fault().. Can you remove the test? > do_sync_mmap_readahead is called in a major page fault context. Right. This is irrelevant however, because if pa_pages==0, the page faults will normally be major ones. Thanks, Fengguang > >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