From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758496Ab1GKXCS (ORCPT ); Mon, 11 Jul 2011 19:02:18 -0400 Received: from wnohang.net ([178.79.154.173]:39483 "EHLO mail.wnohang.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758474Ab1GKXCQ (ORCPT ); Mon, 11 Jul 2011 19:02:16 -0400 X-DKIM: Sendmail DKIM Filter v2.8.3 mail.wnohang.net 84DC0F0007 X-DKIM: Sendmail DKIM Filter v2.8.3 mail.wnohang.net 186FFF0003 Date: Tue, 12 Jul 2011 04:32:09 +0530 From: Raghavendra D Prabhu To: Wu Fengguang Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "akpm@linux-foundation.org" Subject: Re. Revised [PATCH 3/3] mm/readahead: Remove the check for ra->ra_pages Message-ID: <20110711230209.GA39196@Xye> References: <323ddfc402a7f7b94f0cb02bba15acb2acca786f.1310239575.git.rprabhu@wnohang.net> <20110709205308.GC17463@localhost> <20110710125909.GA4460@Xye> <20110710155906.GB7432@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20110710155906.GB7432@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 * On Sun, Jul 10, 2011 at 08:59:06AM -0700, Wu Fengguang wrote: >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? I have removed that test. Patch attached. > >> 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 > > ====================================================================== The check for ra->ra_pages is not required since fs like tmpfs which have ra_pages set to 0 don't use filemap_fault as part of their VMA ops (it uses shmem_fault). Also, page_cache_sync_readahead does its own check for ra_pages. Signed-off-by: Raghavendra D Prabhu --- mm/filemap.c | 2 -- 1 files changed, 0 insertions(+), 2 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 074c23d..0bcd276 100644 --- 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, -- 1.7.6 -------------------------- Raghavendra Prabhu GPG Id : 0xD72BE977 Fingerprint: B93F EBCB 8E05 7039 CD3C A4B8 A616 DCA1 D72B E977 www: wnohang.net