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 X-Spam-Level: X-Spam-Status: No, score=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 25327C433FE for ; Fri, 4 Dec 2020 03:07:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE30922512 for ; Fri, 4 Dec 2020 03:07:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726898AbgLDDHJ (ORCPT ); Thu, 3 Dec 2020 22:07:09 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45012 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726158AbgLDDHJ (ORCPT ); Thu, 3 Dec 2020 22:07:09 -0500 Received: from mail-pl1-x644.google.com (mail-pl1-x644.google.com [IPv6:2607:f8b0:4864:20::644]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D4E07C061A51 for ; Thu, 3 Dec 2020 19:06:28 -0800 (PST) Received: by mail-pl1-x644.google.com with SMTP id p6so2322420plr.7 for ; Thu, 03 Dec 2020 19:06:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=ViR6Izd8QapysirlVQPOGTU6sGViWusybyXG5Wpai50=; b=W0ntIYl7t+F+xana+T1oCCKUDfhGHeqSS8U3VLg4FhyXZYPHpWTXq2vWKpyeLi3/Yf Crz7wvqFDF9OY17Mu123OctxkjmjHYxy1iiHWpKOIwqMu657FD5F9fgjXoEm74nMiVe4 W7b7kMBqBG6c18L9pSirCPjbIjNZ77iaQnIs2UgxpL7V9LljsM4jJdW1avs8GOdWk/Yr FoQjuHc/NGax7AXEJqi0yfCj56HDaK710RTfgYkJMsADGIIOAdfPLf7+Un2hOhfR/buU uK5NWLjaW/vXxyQVsa7YX0gMiPIQ/QCR+hB7fs02bcPp26ADXhsLyepVhkxiUTQP/Wbp P/ag== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=ViR6Izd8QapysirlVQPOGTU6sGViWusybyXG5Wpai50=; b=NHAJwfmABvvIAIUWE6Xe338gpH5VTGQX8YnwHiy7jMlF06NbgqRHce7SJhIg9Fx+dq vXSHN95MMOWpcRBiZBNAM3r9BlChDsbT5jq6HH1ClI+YaFiPz2FdvUaXEwIx1zhr/KjQ PVJcbPW08bXejHr0EA9W3uYvBe3nYO+jo+HxLRf9LXdXt4j4c/8fGZip8PcCLVx8o0Z5 bDR9TVVs+ozz5BRK5Oyekiv3bQ4Jj4EX6tB/ySmNqWRDDHFuNK8QqCKbk2IXj55bdkCt S14DBhrPWoyhSX+mnAYR9A39UjGLMUjGK6W0lfirRGetLFbuxM6nLBoXTd3NQHps7MC+ wH2Q== X-Gm-Message-State: AOAM532YZRCzig6pofIB2otKCMT0vcrBkiqy6EMGWX7ZASICmH2vBlH/ wIhggX9Tu5FOam1k+CyrBSpNmZeLtSY= X-Google-Smtp-Source: ABdhPJzZ82V6GDP7xaj8x0vHnYFfwpWtL71yY+0ySdsPlfuSnhslp/rD5xbnFy16Cft6TOdrbj1/ag== X-Received: by 2002:a17:90a:1c09:: with SMTP id s9mr2100123pjs.83.1607051188435; Thu, 03 Dec 2020 19:06:28 -0800 (PST) Received: from VM-0-6-centos.localdomain ([119.28.90.140]) by smtp.gmail.com with ESMTPSA id w22sm2959219pfu.33.2020.12.03.19.06.27 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 03 Dec 2020 19:06:27 -0800 (PST) From: Chunguang Xu X-Google-Original-From: Chunguang Xu To: tytso@mit.edu, adilger.kernel@dilger.ca Cc: bzzz@whamcloud.com, linux-ext4@vger.kernel.org Subject: [PATCH v2] ext4: avoid s_mb_prefetch to be zero in individual scenarios Date: Fri, 4 Dec 2020 11:05:43 +0800 Message-Id: <1607051143-24508-1-git-send-email-brookxu@tencent.com> X-Mailer: git-send-email 1.8.3.1 Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org From: Chunguang Xu patch cfd7323 introduces block bitmap prefetch, and expects to read block bitmaps of flex_bg through an IO. However, it seems to ignore the value range of s_log_groups_per_flex. In the scenario where the value of s_log_groups_per_flex is greater than 27, s_mb_prefetch or s_mb_prefetch_limit will overflow, cause a divide zero exception. In addition, the logic of calculating nr maybe also flawed, because the size of flexbg is fixed during a single mount, but s_mb_prefetch can be modified, which causes nr to fail to meet the value condition of [1, flexbg_size]. PID: 3873 TASK: ffff88800f11d880 CPU: 2 COMMAND: "executor.4" #0 [ffff8880114a6ec0] __show_regs.cold.7 at ffffffff83cf29e2 #1 [ffff8880114a6f40] do_trap at ffffffff81065c61 #2 [ffff8880114a6f98] do_error_trap at ffffffff81065d65 #3 [ffff8880114a6fe0] exc_divide_error at ffffffff83dd2fd4 #4 [ffff8880114a7000] asm_exc_divide_error at ffffffff83e00872 [exception RIP: ext4_mb_regular_allocator+3885] RIP: ffffffff8191258d RSP: ffff8880114a70b8 RFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff8191257a RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005 RBP: 0000000000000200 R8: ffff88800f11d880 R9: ffffed1001e23b11 R10: ffff88800f11d887 R11: ffffed1001e23b10 R12: ffff888010147000 R13: 0000000000000000 R14: 0000000000000002 R15: dffffc0000000000 ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018 #5 [ffff8880114a7260] ext4_mb_new_blocks at ffffffff8191b6ba #6 [ffff8880114a7420] ext4_new_meta_blocks at ffffffff81870d6f #7 [ffff8880114a74e8] ext4_xattr_block_set at ffffffff819ced37 #8 [ffff8880114a7758] ext4_xattr_set_handle at ffffffff819d4776 #9 [ffff8880114a7928] ext4_xattr_set at ffffffff819d501b RIP: 000000000045eb29 RSP: 00007ff74e97bc38 RFLAGS: 00000246 RAX: ffffffffffffffda RBX: 000000000055bf00 RCX: 000000000045eb29 RDX: 00000000200000c0 RSI: 0000000020000080 RDI: 0000000020000040 RBP: 00000000004b068e R8: 0000000000000001 R9: 0000000000000000 R10: 0000000000000002 R11: 0000000000000246 R12: 000000000055bf00 R13: 00007fff50fc111f R14: 00007ff74e97bdc0 R15: 0000000000022000 ORIG_RAX: 00000000000000bc CS: 0033 SS: 002b To solve this problem, we need to set the upper limit of s_mb_prefetch. Since we expect to load block bitmaps of a flex_bg through an IO, we can consider determining a reasonable upper limit among the IO limit parameters. Comprehensive consideration, we take BLK_MAX_SEGMENT_SIZE. This maybe a good choice to solve divide zero problem and avoiding performance degradation. Reported-by: Tosk Robot Signed-off-by: Chunguang Xu Reviewed-by: Samuel Liao Reviewed-by: Andreas Dilger --- fs/ext4/mballoc.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index 24af9ed..e3ea7af 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -2395,9 +2395,10 @@ void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group, nr = sbi->s_mb_prefetch; if (ext4_has_feature_flex_bg(sb)) { - nr = (group / sbi->s_mb_prefetch) * - sbi->s_mb_prefetch; - nr = nr + sbi->s_mb_prefetch - group; + nr = 1 << sbi->s_log_groups_per_flex; + if (group & (nr - 1)) + nr -= group & (nr - 1); + nr = min(nr, sbi->s_mb_prefetch); } prefetch_grp = ext4_mb_prefetch(sb, group, nr, &prefetch_ios); @@ -2732,8 +2733,12 @@ static int ext4_mb_init_backend(struct super_block *sb) } if (ext4_has_feature_flex_bg(sb)) { + int len; + /* a single flex group is supposed to be read by a single IO */ - sbi->s_mb_prefetch = 1 << sbi->s_es->s_log_groups_per_flex; + len = min(BLK_MAX_SEGMENT_SIZE >> (sb->s_blocksize_bits - 9), + 1 << sbi->s_es->s_log_groups_per_flex); + sbi->s_mb_prefetch = len; sbi->s_mb_prefetch *= 8; /* 8 prefetch IOs in flight at most */ } else { sbi->s_mb_prefetch = 32; -- 1.8.3.1