From: jing zhang Subject: Re: [PATCH] ext4: group cache is added in ext4_mb_discard_preallocations() Date: Wed, 31 Mar 2010 23:10:02 +0800 Message-ID: References: <87wrwty7tx.fsf@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Cc: linux-ext4 , "Theodore Ts'o" , Andreas Dilger , Dave Kleikamp To: "Aneesh Kumar K. V" Return-path: Received: from mail-yw0-f172.google.com ([209.85.211.172]:36604 "EHLO mail-yw0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752505Ab0CaPKE (ORCPT ); Wed, 31 Mar 2010 11:10:04 -0400 Received: by ywh2 with SMTP id 2so103697ywh.33 for ; Wed, 31 Mar 2010 08:10:03 -0700 (PDT) In-Reply-To: <87wrwty7tx.fsf@linux.vnet.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: 2010/3/31, Aneesh Kumar K. V : > On Tue, 30 Mar 2010 20:36:17 +0800, jing zhang wrote: >> From: Jing Zhang >> >> Date: Tue Mar 30 20:35:22 2010 >> >> With the added cache, better group locality may be earned when >> allocating blocks. >> >> Cc: Theodore Ts'o >> Cc: Andreas Dilger >> Cc: Dave Kleikamp >> Cc: "Aneesh Kumar K. V" >> Signed-off-by: Jing Zhang >> >> --- >> >> --- linux-2.6.32/fs/ext4/mballoc.c 2009-12-03 11:51:22.000000000 +0800 >> +++ ext4_mm_leak/mballoc-13.c 2010-03-30 20:28:08.000000000 +0800 >> @@ -4183,12 +4183,20 @@ static int ext4_mb_discard_preallocation >> ext4_group_t i, ngroups = ext4_get_groups_count(sb); >> int ret; >> int freed = 0; >> + static ext4_group_t grp_cache = 0; >> >> trace_ext4_mb_discard_preallocations(sb, needed); >> - for (i = 0; i < ngroups && needed > 0; i++) { >> - ret = ext4_mb_discard_group_preallocations(sb, i, needed); >> + if (needed <= 0) >> + return freed; >> + for (i = 0; i < ngroups; i++) { >> + if (grp_cache >= ngroups) >> + grp_cache -= ngroups; >> + ret = ext4_mb_discard_group_preallocations(sb, grp_cache, needed); >> freed += ret; >> needed -= ret; >> + if (needed <= 0) >> + break; >> + grp_cache++; >> } >> >> return freed; > > can you explain this further ? > > -aneesh > The added cache checks whether blocks pre-allocated in group are still available. If yes, they are discarded and used for allocation without change of group. So more group locality can be earned. What is more, in function, ext4_mb_discard_group_preallocations(), pre-allocation is allowed to be discarded as much as possible by yielding. - zj