From: Alex Tomas Subject: Re: Updated ext4/jbd2 patches based on 2.6.19-rc1 Date: Fri, 06 Oct 2006 14:31:59 +0400 Message-ID: References: <1160072610.8508.12.camel@kleikamp.austin.ibm.com> <20061005205526.7fe744f5.akpm@osdl.org> <20061005215442.310b7792.rdunlap@xenotime.net> <20061006055305.GG22010@schatzie.adilger.int> <20061005230401.0159e31b.akpm@osdl.org> <20061006064103.GJ22010@schatzie.adilger.int> <20061005235017.cbc4fdab.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andreas Dilger , Randy Dunlap , Dave Kleikamp , ext4 development Return-path: Received: from [80.71.248.82] ([80.71.248.82]:10157 "EHLO gw.home.net") by vger.kernel.org with ESMTP id S1751422AbWJFKay (ORCPT ); Fri, 6 Oct 2006 06:30:54 -0400 To: Andrew Morton Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org >>>>> Andrew Morton (AM) writes: AM> On Fri, 6 Oct 2006 00:41:03 -0600 AM> Andreas Dilger wrote: >> The big performance win will come with mballoc and delalloc. CFS has >> been using mballoc for a few years already with Lustre, and IBM + Bull >> did a lot of benchmarking on it. The reason it isn't in the first set of >> patches is partly a manageability issue, and partly because it doesn't >> directly affect the on-disk format (outside of much better allocation) >> so it isn't critical to get into the first round of changes. I believe >> Alex is working on a new set of patches right now. AM> Are you sure that these things will improve allocation much? Reservations AM> made a big improvement there. it depends on underlaying storage and workload. mballoc uses buddy internally. it's much simpler and cheaper to find free 2^N blocks compared to bitmap. this is especially important for arrays like DDN and raid5/6 because they require stripe-aligned/-sized requests for good throughput. also, last mballoc takes logical block into account and can preallocate few chunks at different logical offsets for a file. imagine torrent downloading different pieces from few peers. thanks, Alex