From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx177.postini.com [74.125.245.177]) by kanga.kvack.org (Postfix) with SMTP id D10C16B0044 for ; Wed, 22 Aug 2012 21:10:11 -0400 (EDT) Received: by pbbro12 with SMTP id ro12so357243pbb.14 for ; Wed, 22 Aug 2012 18:10:11 -0700 (PDT) Date: Thu, 23 Aug 2012 09:10:03 +0800 From: Shaohua Li Subject: Re: [patch]readahead: fault retry breaks mmap file read random detection Message-ID: <20120823011003.GA8944@kernel.org> References: <20120822034012.GA24099@kernel.org> <5034FD71.3000406@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5034FD71.3000406@redhat.com> Sender: owner-linux-mm@kvack.org List-ID: To: Rik van Riel Cc: linux-mm@kvack.org, fengguang.wu@intel.com, akpm@linux-foundation.org On Wed, Aug 22, 2012 at 11:40:33AM -0400, Rik van Riel wrote: > On 08/21/2012 11:40 PM, Shaohua Li wrote: > >.fault now can retry. The retry can break state machine of .fault. In > >filemap_fault, if page is miss, ra->mmap_miss is increased. In the second try, > >since the page is in page cache now, ra->mmap_miss is decreased. And these are > >done in one fault, so we can't detect random mmap file access. > > > >Add a new flag to indicate .fault is tried once. In the second try, skip > >ra->mmap_miss decreasing. The filemap_fault state machine is ok with it. > > >Index: linux/arch/avr32/mm/fault.c > >=================================================================== > >--- linux.orig/arch/avr32/mm/fault.c 2012-08-22 09:51:23.035526683 +0800 > >+++ linux/arch/avr32/mm/fault.c 2012-08-22 09:52:22.822775020 +0800 > >@@ -152,6 +152,7 @@ good_area: > > tsk->min_flt++; > > if (fault & VM_FAULT_RETRY) { > > flags &= ~FAULT_FLAG_ALLOW_RETRY; > >+ flags |= FAULT_FLAG_TRIED; > > Is there any place where you set FAULT_FLAG_TRIED > where FAULT_FLAG_ALLOW_RETRY is not cleared? > > In other words, could we use the absence of the > FAULT_FLAG_ALLOW_RETRY as the test, avoiding the > need for a new bit flag? There are still several archs (~7) don't enable fault retry yet. For such archs, FAULT_FLAG_ALLOW_RETRY isn't set in the first try. If all archs support fault retry, the new flag is unnecessary. Thanks, Shaohua -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org