From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EF67AECAAD2 for ; Fri, 2 Sep 2022 00:53:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232831AbiIBAx4 (ORCPT ); Thu, 1 Sep 2022 20:53:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43984 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232705AbiIBAxz (ORCPT ); Thu, 1 Sep 2022 20:53:55 -0400 Received: from out20-157.mail.aliyun.com (out20-157.mail.aliyun.com [115.124.20.157]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ED59283BC3 for ; Thu, 1 Sep 2022 17:53:52 -0700 (PDT) X-Alimail-AntiSpam: AC=CONTINUE;BC=0.05089463|-1;BR=01201311R141S00rulernew998_84748_2000303;CH=blue;DM=|CONTINUE|false|;DS=CONTINUE|ham_regular_dialog|0.00497932-0.000514933-0.994506;FP=0|0|0|0|0|-1|-1|-1;HT=ay29a033018047199;MF=wangyugui@e16-tech.com;NM=1;PH=DS;RN=2;RT=2;SR=0;TI=SMTPD_---.P5gytX5_1662080000; Received: from 192.168.2.112(mailfrom:wangyugui@e16-tech.com fp:SMTPD_---.P5gytX5_1662080000) by smtp.aliyun-inc.com; Fri, 02 Sep 2022 08:53:20 +0800 Date: Fri, 02 Sep 2022 08:53:23 +0800 From: Wang Yugui To: fdmanana@kernel.org Subject: Re: [PATCH 00/10] btrfs: make lseek and fiemap much more efficient Cc: linux-btrfs@vger.kernel.org In-Reply-To: References: Message-Id: <20220902085320.642A.409509F4@e16-tech.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailer: Becky! ver. 2.75.04 [en] Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org Hi, > From: Filipe Manana > > We often get reports of fiemap and hole/data seeking (lseek) being too slow > on btrfs, or even unusable in some cases due to being extremely slow. > > Some recent reports for fiemap: > > https://lore.kernel.org/linux-btrfs/21dd32c6-f1f9-f44a-466a-e18fdc6788a7@virtuozzo.com/ > https://lore.kernel.org/linux-btrfs/Ysace25wh5BbLd5f@atmark-techno.com/ > > For lseek (LSF/MM from 2017): > > https://lwn.net/Articles/718805/ > > Basically both are slow due to very high algorithmic complexity which > scales badly with the number of extents in a file and the heigth of > subvolume and extent b+trees. > > Using Pavel's test case (first Link tag for fiemap), which uses files with > many 4K extents and holes before and after each extent (kind of a worst > case scenario), the speedup is of several orders of magnitude (for the 1G > file, from ~225 seconds down to ~0.1 seconds). > > Finally the new algorithm for fiemap also ends up solving a bug with the > current algorithm. This happens because we are currently relying on extent > maps to report extents, which can be merged, and this may cause us to > report 2 different extents as a single one that is not shared but one of > them is shared (or the other way around). More details on this on patches > 9/10 and 10/10. > > Patches 1/10 and 2/10 are for lseek, introducing some code that will later > be used by fiemap too (patch 10/10). More details in the changelogs. > > There are a few more things that can be done to speedup fiemap and lseek, > but I'll leave those other optimizations I have in mind for some other time. > > Filipe Manana (10): > btrfs: allow hole and data seeking to be interruptible > btrfs: make hole and data seeking a lot more efficient > btrfs: remove check for impossible block start for an extent map at fiemap > btrfs: remove zero length check when entering fiemap > btrfs: properly flush delalloc when entering fiemap > btrfs: allow fiemap to be interruptible > btrfs: rename btrfs_check_shared() to a more descriptive name > btrfs: speedup checking for extent sharedness during fiemap > btrfs: skip unnecessary extent buffer sharedness checks during fiemap > btrfs: make fiemap more efficient and accurate reporting extent sharedness > > fs/btrfs/backref.c | 153 ++++++++- > fs/btrfs/backref.h | 20 +- > fs/btrfs/ctree.h | 22 +- > fs/btrfs/extent-tree.c | 10 +- > fs/btrfs/extent_io.c | 703 ++++++++++++++++++++++++++++------------- > fs/btrfs/file.c | 439 +++++++++++++++++++++++-- > fs/btrfs/inode.c | 146 ++------- > 7 files changed, 1111 insertions(+), 382 deletions(-) An infinite loop happen when the 10 pathes applied to 6.0-rc3. a file is created by 'pavels-test.c' of [PATCH 10/10]. and then '/bin/cp /mnt/test/file1 /dev/null' will trigger an infinite loop. 'sysrq -l' output: [ 1437.765228] Call Trace: [ 1437.765228] [ 1437.765228] set_extent_bit+0x33d/0x6e0 [btrfs] [ 1437.765228] lock_extent_bits+0x64/0xa0 [btrfs] [ 1437.765228] btrfs_file_llseek+0x192/0x5b0 [btrfs] [ 1437.765228] ksys_lseek+0x64/0xb0 [ 1437.765228] do_syscall_64+0x58/0x80 [ 1437.765228] ? syscall_exit_to_user_mode+0x12/0x30 [ 1437.765228] ? do_syscall_64+0x67/0x80 [ 1437.765228] ? do_syscall_64+0x67/0x80 [ 1437.765228] ? exc_page_fault+0x64/0x140 [ 1437.765228] entry_SYSCALL_64_after_hwframe+0x63/0xcd [ 1437.765228] RIP: 0033:0x7f5a263441bb Best Regards Wang Yugui (wangyugui@e16-tech.com) 2022/09/02