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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 autolearn=unavailable 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 04105CA9EC6 for ; Wed, 30 Oct 2019 17:08:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C79082083E for ; Wed, 30 Oct 2019 17:08:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="sgJTl1hj" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727227AbfJ3RIn (ORCPT ); Wed, 30 Oct 2019 13:08:43 -0400 Received: from userp2130.oracle.com ([156.151.31.86]:56642 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726619AbfJ3RIm (ORCPT ); Wed, 30 Oct 2019 13:08:42 -0400 Received: from pps.filterd (userp2130.oracle.com [127.0.0.1]) by userp2130.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x9UH4nuM134508; Wed, 30 Oct 2019 17:08:38 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=date : from : to : cc : subject : message-id : references : mime-version : content-type : in-reply-to; s=corp-2019-08-05; bh=w5NxvYKjEYCfNJ7W5YyboDZSWiIoO9e09L0+NpAonc0=; b=sgJTl1hjenETeET4AXrr9AmQNA+IJsCeqvcpeDiBCtQU1EbG1ZWS6gPr1xFT1o3fH+WD /4uuS5aE0mWNhO31VwE7TMnnARd7nos8TRpPf3mLLq18mIKqBjCjUEkTaEdHwDbSEls6 0QXvhDt1ttEhtDzbQLH6ZN93JRbLZftAtxncBfTNPfZZVWuq4qOjkP1C8tiRBAF2MYVU GKxQQ1mghP2DlEaopc6ZHeDvvG6oQxLQN4Uk/s8iEc9VK9IPwsMEp6d+ZPYqoGRxaSCb emmvmwVymtWhceLigrk7NnkDWdiVtlbSEYdKLMWEo+bL1x/YkuVMUQsQSM4Znced6iex ag== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by userp2130.oracle.com with ESMTP id 2vxwhfnqx3-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 30 Oct 2019 17:08:38 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x9UGrYOw116014; Wed, 30 Oct 2019 17:08:37 GMT Received: from userv0121.oracle.com (userv0121.oracle.com [156.151.31.72]) by aserp3030.oracle.com with ESMTP id 2vxwjab2ta-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 30 Oct 2019 17:08:37 +0000 Received: from abhmp0021.oracle.com (abhmp0021.oracle.com [141.146.116.27]) by userv0121.oracle.com (8.14.4/8.13.8) with ESMTP id x9UH8ZYJ013475; Wed, 30 Oct 2019 17:08:35 GMT Received: from localhost (/67.169.218.210) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 30 Oct 2019 10:08:34 -0700 Date: Wed, 30 Oct 2019 10:08:33 -0700 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 01/26] xfs: Lower CIL flush limit for large logs Message-ID: <20191030170833.GL15222@magnolia> References: <20191009032124.10541-1-david@fromorbit.com> <20191009032124.10541-2-david@fromorbit.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191009032124.10541-2-david@fromorbit.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9426 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=2 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910300151 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9426 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1910300151 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Oct 09, 2019 at 02:20:59PM +1100, Dave Chinner wrote: > From: Dave Chinner > > The current CIL size aggregation limit is 1/8th the log size. This > means for large logs we might be aggregating at least 250MB of dirty objects > in memory before the CIL is flushed to the journal. With CIL shadow > buffers sitting around, this means the CIL is often consuming >500MB > of temporary memory that is all allocated under GFP_NOFS conditions. > > Flushing the CIL can take some time to do if there is other IO > ongoing, and can introduce substantial log force latency by itself. > It also pins the memory until the objects are in the AIL and can be > written back and reclaimed by shrinkers. Hence this threshold also > tends to determine the minimum amount of memory XFS can operate in > under heavy modification without triggering the OOM killer. > > Modify the CIL space limit to prevent such huge amounts of pinned > metadata from aggregating. We can have 2MB of log IO in flight at > once, so limit aggregation to 16x this size. This threshold was > chosen as it little impact on performance (on 16-way fsmark) or log > traffic but pins a lot less memory on large logs especially under > heavy memory pressure. An aggregation limit of 8x had 5-10% > performance degradation and a 50% increase in log throughput for > the same workload, so clearly that was too small for highly > concurrent workloads on large logs. > > This was found via trace analysis of AIL behaviour. e.g. insertion > from a single CIL flush: > > xfs_ail_insert: old lsn 0/0 new lsn 1/3033090 type XFS_LI_INODE flags IN_AIL > > $ grep xfs_ail_insert /mnt/scratch/s.t |grep "new lsn 1/3033090" |wc -l > 1721823 > $ > > So there were 1.7 million objects inserted into the AIL from this > CIL checkpoint, the first at 2323.392108, the last at 2325.667566 which > was the end of the trace (i.e. it hadn't finished). Clearly a major > problem. > > Signed-off-by: Dave Chinner Reviewed-by: Darrick J. Wong --D > --- > fs/xfs/xfs_log_priv.h | 29 +++++++++++++++++++++++------ > 1 file changed, 23 insertions(+), 6 deletions(-) > > diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h > index b880c23cb6e4..a3cc8a9a16d9 100644 > --- a/fs/xfs/xfs_log_priv.h > +++ b/fs/xfs/xfs_log_priv.h > @@ -323,13 +323,30 @@ struct xfs_cil { > * tries to keep 25% of the log free, so we need to keep below that limit or we > * risk running out of free log space to start any new transactions. > * > - * In order to keep background CIL push efficient, we will set a lower > - * threshold at which background pushing is attempted without blocking current > - * transaction commits. A separate, higher bound defines when CIL pushes are > - * enforced to ensure we stay within our maximum checkpoint size bounds. > - * threshold, yet give us plenty of space for aggregation on large logs. > + * In order to keep background CIL push efficient, we only need to ensure the > + * CIL is large enough to maintain sufficient in-memory relogging to avoid > + * repeated physical writes of frequently modified metadata. If we allow the CIL > + * to grow to a substantial fraction of the log, then we may be pinning hundreds > + * of megabytes of metadata in memory until the CIL flushes. This can cause > + * issues when we are running low on memory - pinned memory cannot be reclaimed, > + * and the CIL consumes a lot of memory. Hence we need to set an upper physical > + * size limit for the CIL that limits the maximum amount of memory pinned by the > + * CIL but does not limit performance by reducing relogging efficiency > + * significantly. > + * > + * As such, the CIL push threshold ends up being the smaller of two thresholds: > + * - a threshold large enough that it allows CIL to be pushed and progress to be > + * made without excessive blocking of incoming transaction commits. This is > + * defined to be 12.5% of the log space - half the 25% push threshold of the > + * AIL. > + * - small enough that it doesn't pin excessive amounts of memory but maintains > + * close to peak relogging efficiency. This is defined to be 16x the iclog > + * buffer window (32MB) as measurements have shown this to be roughly the > + * point of diminishing performance increases under highly concurrent > + * modification workloads. > */ > -#define XLOG_CIL_SPACE_LIMIT(log) (log->l_logsize >> 3) > +#define XLOG_CIL_SPACE_LIMIT(log) \ > + min_t(int, (log)->l_logsize >> 3, BBTOB(XLOG_TOTAL_REC_SHIFT(log)) << 4) > > /* > * ticket grant locks, queues and accounting have their own cachlines > -- > 2.23.0.rc1 >