From nobody Sun Sep 14 03:50:47 2025 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 55896C7EE23 for ; Tue, 30 May 2023 12:41:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230164AbjE3MlI (ORCPT ); Tue, 30 May 2023 08:41:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38982 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229568AbjE3MlF (ORCPT ); Tue, 30 May 2023 08:41:05 -0400 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 864EB102; Tue, 30 May 2023 05:40:40 -0700 (PDT) Received: from pps.filterd (m0356517.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 34UCNvJA001911; Tue, 30 May 2023 12:34:01 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : mime-version : content-transfer-encoding; s=pp1; bh=+BnaDz8GOFXK9Oo3BhAJjGeaM8iWRw27pFgOHNngyF0=; b=gM/wS2SPf5FIc+fIV1j8oWiRfV465rz+BEbTYy4VbR0BCP1hdAOulBuDTxp6sUiDQKly aINYu9qVJW+rWng6+cMTJsZjDh43QJtRMgrbwcKfS1gRdXoLp7iBApJkC+u2mlJk4avv LjbqF46OGuj/dtmmIMn9CoeuvyMv8Yi7TU2/zEFsm8WQ5lHXDhLVkUp7+m9fzksgZwIc KNYBPeFDg4jDlqmHDy8IOO1bnLEOlC2LSOeEZuKig7ADgq+ORkFPBC2lqn0t2Yxxacma aoOFC4oPvNN8gKLplE/X3tcWjgR7vcAwUyBSyLp9TbO8ucmgCDw/Utfbhkml/OeXZrPo cA== Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 3qwh46r8gh-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 30 May 2023 12:34:00 +0000 Received: from m0356517.ppops.net (m0356517.ppops.net [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 34UCPBkp005122; Tue, 30 May 2023 12:34:00 GMT Received: from ppma04ams.nl.ibm.com (63.31.33a9.ip4.static.sl-reverse.com [169.51.49.99]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 3qwh46r8f3-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 30 May 2023 12:34:00 +0000 Received: from pps.filterd (ppma04ams.nl.ibm.com [127.0.0.1]) by ppma04ams.nl.ibm.com (8.17.1.19/8.17.1.19) with ESMTP id 34U2f7Gt007278; Tue, 30 May 2023 12:33:58 GMT Received: from smtprelay06.fra02v.mail.ibm.com ([9.218.2.230]) by ppma04ams.nl.ibm.com (PPS) with ESMTPS id 3qu9g59fdv-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 30 May 2023 12:33:57 +0000 Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay06.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 34UCXtJa28967358 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 30 May 2023 12:33:55 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 646472004B; Tue, 30 May 2023 12:33:55 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6627820040; Tue, 30 May 2023 12:33:53 +0000 (GMT) Received: from li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.in.ibm.com (unknown [9.109.253.169]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 30 May 2023 12:33:53 +0000 (GMT) From: Ojaswin Mujoo To: linux-ext4@vger.kernel.org, "Theodore Ts'o" Cc: Ritesh Harjani , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jan Kara , Kemeng Shi , Ritesh Harjani Subject: [PATCH v2 01/12] Revert "ext4: remove ac->ac_found > sbi->s_mb_min_to_scan dead check in ext4_mb_check_limits" Date: Tue, 30 May 2023 18:03:39 +0530 Message-Id: X-Mailer: git-send-email 2.31.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: MKzok8uVa59I_SxTeep2p2vJ_uz6d4jo X-Proofpoint-GUID: gWtt9MZouc8fyq9c5n5xISEDpgCVchP2 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.573,FMLib:17.11.176.26 definitions=2023-05-30_08,2023-05-30_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 priorityscore=1501 suspectscore=0 impostorscore=0 lowpriorityscore=0 phishscore=0 clxscore=1015 adultscore=0 mlxlogscore=996 mlxscore=0 bulkscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2304280000 definitions=main-2305300103 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" This reverts commit 32c0869370194ae5ac9f9f501953ef693040f6a1. The reverted commit was intended to remove a dead check however it was obse= rved that this check was actually being used to exit early instead of looping sbi->s_mb_max_to_scan times when we are able to find a free extent bigger t= han the goal extent. Due to this, a my performance tests (fsmark, parallel file writes in a highly fragmented FS) were seeing a 2x-3x regression. Example, the default value of the following variables is: sbi->s_mb_max_to_scan =3D 200 sbi->s_mb_min_to_scan =3D 10 In ext4_mb_check_limits() if we find an extent smaller than goal, then we r= eturn early and try again. This loop will go on until we have processed sbi->s_mb_max_to_scan(=3D200) number of free extents at which point we exit= and just use whatever we have even if it is smaller than goal extent. Now, the regression comes when we find an extent bigger than goal. Earlier,= in this case we would loop only sbi->s_mb_min_to_scan(=3D10) times and then ju= st use the bigger extent. However with commit 32c08693 that check was removed and = hence we would loop sbi->s_mb_max_to_scan(=3D200) times even though we have a big= enough free extent to satisfy the request. The only time we would exit early would= be when the free extent is *exactly* the size of our goal, which is pretty unc= ommon occurrence and so we would almost always end up looping 200 times. Hence, revert the commit by adding the check back to fix the regression. Al= so add a comment to outline this policy. Signed-off-by: Ojaswin Mujoo Reviewed-by: Ritesh Harjani (IBM) Reviewed-by: Kemeng Shi --- fs/ext4/mballoc.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index d4b6a2c1881d..7ac6d3524f29 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -2063,7 +2063,7 @@ static void ext4_mb_check_limits(struct ext4_allocati= on_context *ac, if (bex->fe_len < gex->fe_len) return; =20 - if (finish_group) + if (finish_group || ac->ac_found > sbi->s_mb_min_to_scan) ext4_mb_use_best_found(ac, e4b); } =20 @@ -2075,6 +2075,20 @@ static void ext4_mb_check_limits(struct ext4_allocat= ion_context *ac, * in the context. Later, the best found extent will be used, if * mballoc can't find good enough extent. * + * The algorithm used is roughly as follows: + * + * * If free extent found is exactly as big as goal, then + * stop the scan and use it immediately + * + * * If free extent found is smaller than goal, then keep retrying + * upto a max of sbi->s_mb_max_to_scan times (default 200). After + * that stop scanning and use whatever we have. + * + * * If free extent found is bigger than goal, then keep retrying + * upto a max of sbi->s_mb_min_to_scan times (default 10) before + * stopping the scan and using the extent. + * + * * FIXME: real allocation policy is to be designed yet! */ static void ext4_mb_measure_extent(struct ext4_allocation_context *ac, --=20 2.31.1