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=-5.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,URIBL_BLOCKED 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 C4B79C433DF for ; Sat, 23 May 2020 16:18:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 88CC820878 for ; Sat, 23 May 2020 16:18:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="v0MzPH+R" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727840AbgEWQSp (ORCPT ); Sat, 23 May 2020 12:18:45 -0400 Received: from aserp2120.oracle.com ([141.146.126.78]:34548 "EHLO aserp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727033AbgEWQSo (ORCPT ); Sat, 23 May 2020 12:18:44 -0400 Received: from pps.filterd (aserp2120.oracle.com [127.0.0.1]) by aserp2120.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 04NGIeW6015196; Sat, 23 May 2020 16:18:40 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-2020-01-29; bh=2mYMVZgF3c4RPkzmpblgfiJPKqJqApEQqId/GWbX624=; b=v0MzPH+R2uvWWv46oCGJSqwzx40EtBDh86935r5xmWiGYj0i5XhzUecrUtSQin4HkVUs 84gPCdNy+gVcQ9VjA3eelBgXv/RQASgY250dQvphkM3zMGWrSEeuU/wzYvReKlHXHxP3 +GKuzGN8pSYuZKjxLgH6Ipd6WtoJi90+bzNzJEDuF7ZpdjD8r2qjMW5puA9imZ+6U2H5 fHH1BJr+r/noAAmdgnBnN1QZU0zHoncqPf+2+SRagpwLwyg2M+FPW4K/YtVn873Z+Cyl vb7jS0F/OD14KCcWqxnAPSJMDMY0CXdZOhjFinKWCm6V8L5bLCRRISAe4LgeIDsFeM77 mg== Received: from userp3030.oracle.com (userp3030.oracle.com [156.151.31.80]) by aserp2120.oracle.com with ESMTP id 316uskh5fd-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Sat, 23 May 2020 16:18:40 +0000 Received: from pps.filterd (userp3030.oracle.com [127.0.0.1]) by userp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 04NGIdYO120326; Sat, 23 May 2020 16:18:39 GMT Received: from aserv0121.oracle.com (aserv0121.oracle.com [141.146.126.235]) by userp3030.oracle.com with ESMTP id 316rxrv2kf-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Sat, 23 May 2020 16:18:39 +0000 Received: from abhmp0016.oracle.com (abhmp0016.oracle.com [141.146.116.22]) by aserv0121.oracle.com (8.14.4/8.13.8) with ESMTP id 04NGIZXt000860; Sat, 23 May 2020 16:18:35 GMT Received: from localhost (/10.159.158.181) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Sat, 23 May 2020 09:18:34 -0700 Date: Sat, 23 May 2020 09:18:33 -0700 From: "Darrick J. Wong" To: Dave Chinner Cc: linux-xfs@vger.kernel.org Subject: Re: [PATCH 00/24] xfs: rework inode flushing to make inode reclaim fully asynchronous Message-ID: <20200523161833.GF8230@magnolia> References: <20200522035029.3022405-1-david@fromorbit.com> <20200522040401.GE2040@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200522040401.GE2040@dread.disaster.area> X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9629 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=7 mlxlogscore=999 phishscore=0 spamscore=0 adultscore=0 bulkscore=0 malwarescore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005230134 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9629 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 lowpriorityscore=0 suspectscore=7 spamscore=0 priorityscore=1501 clxscore=1015 impostorscore=0 bulkscore=0 mlxlogscore=999 phishscore=0 cotscore=-2147483648 adultscore=0 mlxscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2005230134 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Fri, May 22, 2020 at 02:04:01PM +1000, Dave Chinner wrote: > > FWIW, I forgot to put it in the original description - the series > can be pulled from my git tree here: > > git://git.kernel.org/pub/scm/linux/kernel/git/dgc/linux-xfs.git xfs-async-inode-reclaim Hmm, so I tried this out with quotas enabled and hit this in xfs/438: MKFS_OPTIONS="-m reflink=1,rmapbt=1 -i sparse=1 /dev/sdf MOUNT_OPTIONS="-o usrquota,grpquota,prjquota" BUG: kernel NULL pointer dereference, address: 0000000000000020 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP CPU: 3 PID: 824887 Comm: xfsaild/dm-0 Tainted: G W 5.7.0-rc4-djw #rc4 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1 04/01/2014 RIP: 0010:do_raw_spin_trylock+0x5/0x40 Code: 64 de 81 48 89 ef e8 ba fe ff ff eb 8b 89 c6 48 89 ef e8 de dc ff ff 66 90 eb 8b 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 <8b> 07 85 c0 75 28 ba 01 00 00 00 f0 0f b1 17 75 1d 65 8b 05 83 d8 RSP: 0018:ffffc90000afbdc0 EFLAGS: 00010086 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffff888070ee0000 RSI: 0000000000000000 RDI: 0000000000000020 RBP: 0000000000000020 R08: 0000000000000001 R09: 0000000000000001 R10: 0000000000000000 R11: ffffc90000afbc3d R12: 0000000000000038 R13: 0000000000000202 R14: 0000000000000003 R15: ffff88800688a600 FS: 0000000000000000(0000) GS:ffff88807e000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000020 CR3: 000000003bba2001 CR4: 00000000001606a0 Call Trace: _raw_spin_lock_irqsave+0x47/0x80 ? down_trylock+0xf/0x30 down_trylock+0xf/0x30 xfs_buf_trylock+0x1a/0x1f0 [xfs] xfsaild+0xb69/0x1320 [xfs] kthread+0x130/0x170 ? xfs_trans_ail_cursor_first+0x80/0x80 [xfs] ? kthread_park+0x90/0x90 ret_from_fork+0x3a/0x50 Modules linked in: dm_thin_pool dm_persistent_data dm_bio_prison btrfs blake2b_generic xor zstd_decompress zstd_compress lzo_compress lzo_decompress zlib_deflate raid6_pq dm_snapshot dm_bufio dm_flakey xfs libcrc32c ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 ip_set_hash_ip xt_REDIRECT ip_set_hash_net xt_set ip_set_hash_mac xt_tcpudp ip_set iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nfnetlink ip6table_filter ip6_tables iptable_filter bfq sch_fq_codel ip_tables x_tables nfsv4 af_packet [last unloaded: scsi_debug] Dumping ftrace buffer: (ftrace buffer empty) CR2: 0000000000000020 ---[ end trace 4ac61a00d1e3b068 ]--- --D > Cheers, > > Dave. > > On Fri, May 22, 2020 at 01:50:05PM +1000, Dave Chinner wrote: > > Hi folks, > > > > Inode flushing requires that we first lock an inode, then check it, > > then lock the underlying buffer, flush the inode to the buffer and > > finally add the inode to the buffer to be unlocked on IO completion. > > We then walk all the other cached inodes in the buffer range and > > optimistically lock and flush them to the buffer without blocking. > > > > This cluster write effectively repeats the same code we do with the > > initial inode, except now it has to special case that initial inode > > that is already locked. Hence we have multiple copies of very > > similar code, and it is a result of inode cluster flushing being > > based on a specific inode rather than grabbing the buffer and > > flushing all available inodes to it. > > > > The problem with this at the moment is that we we can't look up the > > buffer until we have guaranteed that an inode is held exclusively > > and it's not going away while we get the buffer through an imap > > lookup. Hence we are kinda stuck locking an inode before we can look > > up the buffer. > > > > This is also a result of inodes being detached from the cluster > > buffer except when IO is being done. This has the further problem > > that the cluster buffer can be reclaimed from memory and then the > > inode can be dirtied. At this point cleaning the inode requires a > > read-modify-write cycle on the cluster buffer. If we then are put > > under memory pressure, cleaning that dirty inode to reclaim it > > requires allocating memory for the cluster buffer and this leads to > > all sorts of problems. > > > > We used synchronous inode writeback in reclaim as a throttle that > > provided a forwards progress mechanism when RMW cycles were required > > to clean inodes. Async writeback of inodes (e.g. via the AIL) would > > immediately exhaust remaining memory reserves trying to allocate > > inode cluster after inode cluster. The synchronous writeback of an > > inode cluster allowed reclaim to release the inode cluster and have > > it freed almost immediately which could then be used to allocate the > > next inode cluster buffer. Hence the IO based throttling mechanism > > largely guaranteed forwards progress in inode reclaim. By removing > > the requirement for require memory allocation for inode writeback > > filesystem level, we can issue writeback asynchrnously and not have > > to worry about the memory exhaustion anymore. > > > > Another issue is that if we have slow disks, we can build up dirty > > inodes in memory that can then take hours for an operation like > > unmount to flush. A RMW cycle per inode on a slow RAID6 device can > > mean we only clean 50 inodes a second, and when there are hundreds > > of thousands of dirty inodes that need to be cleaned this can take a > > long time. PInning the cluster buffers will greatly speed up inode > > writeback on slow storage systems like this. > > > > These limitations all stem from the same source: inode writeback is > > inode centric, And they are largely solved by the same architectural > > change: make inode writeback cluster buffer centric. This series is > > makes that architectural change. > > > > Firstly, we start by pinning the inode backing buffer in memory > > when an inode is marked dirty (i.e. when it is logged). By tracking > > the number of dirty inodes on a buffer as a counter rather than a > > flag, we avoid the problem of overlapping inode dirtying and buffer > > flushing racing to set/clear the dirty flag. Hence as long as there > > is a dirty inode in memory, the buffer will not be able to be > > reclaimed. We can safely do this inode cluster buffer lookup when we > > dirty an inode as we do not hold the buffer locked - we merely take > > a reference to it and then release it - and hence we don't cause any > > new lock order issues. > > > > When the inode is finally cleaned, the reference to the buffer can > > be removed from the inode log item and the buffer released. This is > > done from the inode completion callbacks that are attached to the > > buffer when the inode is flushed. > > > > Pinning the cluster buffer in this way immediately avoids the RMW > > problem in inode writeback and reclaim contexts by moving the memory > > allocation and the blocking buffer read into the transaction context > > that dirties the inode. This inverts our dirty inode throttling > > mechanism - we now throttle the rate at which we can dirty inodes to > > rate at which we can allocate memory and read inode cluster buffers > > into memory rather than via throttling reclaim to rate at which we > > can clean dirty inodes. > > > > Hence if we are under memory pressure, we'll block on memory > > allocation when trying to dirty the referenced inode, rather than in > > the memory reclaim path where we are trying to clean unreferenced > > inodes to free memory. Hence we no longer have to guarantee > > forwards progress in inode reclaim as we aren't doing memory > > allocation, and that means we can remove inode writeback from the > > XFS inode shrinker completely without changing the system tolerance > > for low memory operation. > > > > Tracking the buffers via the inode log item also allows us to > > completely rework the inode flushing mechanism. While the inode log > > item is in the AIL, it is safe for the AIL to access any member of > > the log item. Hence the AIL push mechanisms can access the buffer > > attached to the inode without first having to lock the inode. > > > > This means we can essentially lock the buffer directly and then > > call xfs_iflush_cluster() without first going through xfs_iflush() > > to find the buffer. Hence we can remove xfs_iflush() altogether, > > because the two places that call it - the inode item push code and > > inode reclaim - no longer need to flush inodes directly. > > > > This can be further optimised by attaching the inode to the cluster > > buffer when the inode is dirtied. i.e. when we add the buffer > > reference to the inode log item, we also attach the inode to the > > buffer for IO processing. This leads to the dirty inodes always > > being attached to the buffer and hence we no longer need to add them > > when we flush the inode and remove them when IO completes. Instead > > the inodes are attached when the node log item is dirtied, and > > removed when the inode log item is cleaned. > > > > With this structure in place, we no longer need to do > > lookups to find the dirty inodes in the cache to attach to the > > buffer in xfs_iflush_cluster() - they are already attached to the > > buffer. Hence when the AIL pushes an inode, we just grab the buffer > > from the log item, and then walk the buffer log item list to lock > > and flush the dirty inodes attached to the buffer. > > > > This greatly simplifies inode writeback, and removes another memory > > allocation from the inode writeback path (the array used for the > > radix tree gang lookup). And while the radix tree lookups are fast, > > walking the linked list of dirty inodes is faster. > > > > There is followup work I am doing that uses the inode cluster buffer > > as a replacement in the AIL for tracking dirty inodes. This part of > > the series is not ready yet as it has some intricate locking > > requirements. That is an optimisation, so I've left that out because > > solving the inode reclaim blocking problems is the important part of > > this work. > > > > In short, this series simplifies inode writeback and fixes the long > > standing inode reclaim blocking issues without requiring any changes > > to the memory reclaim infrastructure. > > > > Note: dquots should probably be converted to cluster flushing in a > > similar way, as they have many of the same issues as inode flushing. > > > > Thoughts, comments and improvemnts welcome. > > > > -Dave. > > > > > > > > Dave Chinner (24): > > xfs: remove logged flag from inode log item > > xfs: add an inode item lock > > xfs: mark inode buffers in cache > > xfs: mark dquot buffers in cache > > xfs: mark log recovery buffers for completion > > xfs: call xfs_buf_iodone directly > > xfs: clean up whacky buffer log item list reinit > > xfs: fold xfs_istale_done into xfs_iflush_done > > xfs: use direct calls for dquot IO completion > > xfs: clean up the buffer iodone callback functions > > xfs: get rid of log item callbacks > > xfs: pin inode backing buffer to the inode log item > > xfs: make inode reclaim almost non-blocking > > xfs: remove IO submission from xfs_reclaim_inode() > > xfs: allow multiple reclaimers per AG > > xfs: don't block inode reclaim on the ILOCK > > xfs: remove SYNC_TRYLOCK from inode reclaim > > xfs: clean up inode reclaim comments > > xfs: attach inodes to the cluster buffer when dirtied > > xfs: xfs_iflush() is no longer necessary > > xfs: rename xfs_iflush_int() > > xfs: rework xfs_iflush_cluster() dirty inode iteration > > xfs: factor xfs_iflush_done > > xfs: remove xfs_inobp_check() > > > > fs/xfs/libxfs/xfs_inode_buf.c | 27 +- > > fs/xfs/libxfs/xfs_inode_buf.h | 6 - > > fs/xfs/libxfs/xfs_trans_inode.c | 108 +++++-- > > fs/xfs/xfs_buf.c | 44 ++- > > fs/xfs/xfs_buf.h | 49 +-- > > fs/xfs/xfs_buf_item.c | 205 +++++-------- > > fs/xfs/xfs_buf_item.h | 8 +- > > fs/xfs/xfs_buf_item_recover.c | 5 +- > > fs/xfs/xfs_dquot.c | 32 +- > > fs/xfs/xfs_dquot.h | 1 + > > fs/xfs/xfs_dquot_item_recover.c | 2 +- > > fs/xfs/xfs_file.c | 9 +- > > fs/xfs/xfs_icache.c | 293 +++++------------- > > fs/xfs/xfs_inode.c | 515 +++++++++++--------------------- > > fs/xfs/xfs_inode.h | 2 +- > > fs/xfs/xfs_inode_item.c | 281 ++++++++--------- > > fs/xfs/xfs_inode_item.h | 9 +- > > fs/xfs/xfs_inode_item_recover.c | 2 +- > > fs/xfs/xfs_log_recover.c | 5 +- > > fs/xfs/xfs_mount.c | 4 - > > fs/xfs/xfs_mount.h | 1 - > > fs/xfs/xfs_trans.h | 3 - > > fs/xfs/xfs_trans_buf.c | 15 +- > > fs/xfs/xfs_trans_priv.h | 12 +- > > 24 files changed, 680 insertions(+), 958 deletions(-) > > > > -- > > 2.26.2.761.g0e0b3e54be > > > > > > -- > Dave Chinner > david@fromorbit.com