From: Ted Ts'o Subject: Re: [PATCH v2] ext4: directly leave out of ext4_find_delalloc_range() if filesystem mount with "nodelalloc" Date: Mon, 19 Dec 2011 10:39:07 -0500 Message-ID: <20111219153907.GA27501@thunk.org> References: <1323237879-31800-1-git-send-email-hao.bigrat@gmail.com> <1323327594-4914-1-git-send-email-hao.bigrat@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-ext4@vger.kernel.org, Robin Dong To: Robin Dong Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:43361 "EHLO test.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751032Ab1LSPjM (ORCPT ); Mon, 19 Dec 2011 10:39:12 -0500 Content-Disposition: inline In-Reply-To: <1323327594-4914-1-git-send-email-hao.bigrat@gmail.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Thu, Dec 08, 2011 at 02:59:54PM +0800, Robin Dong wrote: > From: Robin Dong > > We found performance regression when using bigalloc with "nodelalloc" (1MB cluster size): > > 1. mke2fs -C 1048576 -O ^has_journal,bigalloc /dev/sda > 2. mount -o nodelalloc /dev/sda /test/ > 3. time dd if=/dev/zero of=/test/io bs=1048576 count=1024 > > The "dd" will cost about 2 seconds to finish, but if we mke2fs without "bigalloc", > "dd" will only cost lesss than 1 second. > > The reason is: when using ext4 with "nodelalloc", it will call ext4_find_delalloc_cluster() nearly > everytime it call ext4_ext_map_blocks(), and ext4_find_delalloc_range() will also scan all pages > in cluster because no buffer is "delayed". > A cluster has 256 pages (1MB cluster), so it will scan 256 * 256k pags when creating a 1G file. That > severely hurts the performance. > > Therefore, we return out from ext4_find_delalloc_range() when using "nodelalloc". > > Signed-off-by: Robin Dong Thanks, applied. - Ted