Re: [GIT PULL] xfs: CIL and log scalability improvements

["Darrick J. Wong" <djwong@kernel.org>]

On Fri, Jun 04, 2021 at 01:29:28PM +1000, Dave Chinner wrote:
> Hi Darrick,
> 
> Can you please pull the CIL and log improvements from the tag listed
> below?

I tried that and threw the series at fstests, which crashed all VMs with
the following null pointer dereference:

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0 
Oops: 0000 [#1] PREEMPT SMP
CPU: 2 PID: 731060 Comm: mount Not tainted 5.13.0-rc4-djwx #rc4
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:xlog_cil_init+0x2f7/0x370 [xfs]
Code: b4 7e a0 bf 1c 00 00 00 e8 c6 3b 8d e0 85 c0 78 0c c6 05 13 7f 12 00 01 e9 7b fd ff ff 4
2 48 c7 c6 f8 bf 7f a0 <48> 8b 39 e8 f0 24 04 00 31 ff b9 fc 05 00 00 48 c7 c2 d9 b3 7e a0
RSP: 0018:ffffc9000776bcd0 EFLAGS: 00010286
RAX: 00000000fffffff0 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 00000000fffffff0 RSI: ffffffffa07fbff8 RDI: 00000000ffffffff
RBP: ffff888004cf3c00 R08: ffffffffa078fb40 R09: 0000000000000000
R10: 000000000000000c R11: 0000000000000048 R12: ffff888052810000
R13: 0000607f81c0b0f8 R14: ffff888004a09c00 R15: ffff888004a09c00
FS:  00007fd2e4486840(0000) GS:ffff88807e000000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000528e5004 CR4: 00000000001706a0
Call Trace:
 xlog_alloc_log+0x51f/0x5f0 [xfs]
 xfs_log_mount+0x55/0x340 [xfs]
 xfs_mountfs+0x4e4/0x9f0 [xfs]
 xfs_fs_fill_super+0x4dd/0x7a0 [xfs]
 ? suffix_kstrtoint.constprop.0+0xe0/0xe0 [xfs]
 get_tree_bdev+0x175/0x280
 vfs_get_tree+0x1a/0x80
 ? capable+0x2f/0x50
 path_mount+0x6fb/0xa90
 __x64_sys_mount+0x103/0x140
 do_syscall_64+0x3a/0x70
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7fd2e46e8dde
Code: 48 8b 0d b5 80 0c 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0
f 1e fa 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 82 80 0c 00 f7 d8 64 89 01 48

I'm pretty sure that's due to:

	if (!xlog_cil_pcp_init) {
		int	ret;

		ret = cpuhp_setup_state_nocalls(CPUHP_XFS_CIL_DEAD,
						"xfs/cil_pcp:dead", NULL,
						xlog_cil_pcp_dead);
		if (ret < 0) {
			xfs_warn(cil->xc_log->l_mp,
	"Failed to initialise CIL hotplug, error %d. XFS is non-functional.",
				ret);

Because we haven't set cil->xc_log yet.

--D

> 
> Cheers,
> 
> Dave.
> 
> The following changes since commit d07f6ca923ea0927a1024dfccafc5b53b61cfecc:
> 
>   Linux 5.13-rc2 (2021-05-16 15:27:44 -0700)
> 
> are available in the Git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/dgc/linux-xfs.git tags/xfs-cil-scale-tag
> 
> for you to fetch changes up to 856d6346ad5e76f230906792b1eb4ba70c860748:
> 
>   xfs: expanding delayed logging design with background material (2021-06-04 12:42:29 +1000)
> 
> ----------------------------------------------------------------
> xfs: CIL and log scalability improvements
> 
> Performance improvements are largely documented in the change logs of the
> individual patches. Headline numbers are an increase in transaction rate from
> 700k commits/s to 1.7M commits/s, and a reduction in fua/flush operations by
> 2-3 orders of magnitude on metadata heavy workloads that don't use fsync.
> 
> Summary of series:
> 
> Patches         Modifications
> -------         -------------
> 1-7:            log write FUA/FLUSH optimisations
> 8:              bug fix
> 9-11:           Async CIL pushes
> 12-25:          xlog_write() rework
> 26-39:          CIL commit scalability
> 
> The log write FUA/FLUSH optimisations reduce the number of cache flushes
> required to flush the CIL to the journal. It extends the old pre-delayed logging
> ordering semantics required by writing individual transactions to the iclogs out
> to cover then CIL checkpoint transactions rather than individual writes to the
> iclogs. In doing so, we reduce the cache flush requirements to once per CIL
> checkpoint rather than once per iclog write.
> 
> The async CIL pushes fix a pipeline limitation that only allowed a single CIL
> push to be processed at a time. This was causing CIL checkpoint writing to
> become CPU bound as only a single CIL checkpoint could be pushed at a time. The
> checkpoint pipleine was designed to allow multiple pushes to be in flight at
> once and use careful ordering of the commit records to ensure correct recovery
> order, but the workqueue implementation didn't allow concurrent works to be run.
> The concurrent works now extend out to 4 CIL checkpoints running at a time,
> hence removing the CPU usage limiations without introducing new lock contention
> issues.
> 
> The xlog_write() rework is long overdue. The code is complex, difficult to
> understand, full of tricky, subtle corner cases and just generally really hard
> to modify. This patchset reworks the xlog_write() API to reduce the processing
> overhead of writing out long log vector chains, and factors the xlog_write()
> code into a simple, compact fast path along with a clearer slow path to handle
> the complex cases.
> 
> The CIL commit scalability patchset removes spinlocks from the transaction
> commit fast path. These spinlocks are the performance limiting bottleneck in the
> transaction commit path, so we apply a variety of different techniques to do
> either atomic. lockless or per-cpu updates of the CIL tracking structures during
> commits. This greatly increases the throughput of the the transaction commit
> engine, moving the contention point to the log space tracking algorithms after
> doubling throughput on 32-way workloads.
> 
> ----------------------------------------------------------------
> Dave Chinner (39):
>       xfs: log stripe roundoff is a property of the log
>       xfs: separate CIL commit record IO
>       xfs: remove xfs_blkdev_issue_flush
>       xfs: async blkdev cache flush
>       xfs: CIL checkpoint flushes caches unconditionally
>       xfs: remove need_start_rec parameter from xlog_write()
>       xfs: journal IO cache flush reductions
>       xfs: Fix CIL throttle hang when CIL space used going backwards
>       xfs: xfs_log_force_lsn isn't passed a LSN
>       xfs: AIL needs asynchronous CIL forcing
>       xfs: CIL work is serialised, not pipelined
>       xfs: factor out the CIL transaction header building
>       xfs: only CIL pushes require a start record
>       xfs: embed the xlog_op_header in the unmount record
>       xfs: embed the xlog_op_header in the commit record
>       xfs: log tickets don't need log client id
>       xfs: move log iovec alignment to preparation function
>       xfs: reserve space and initialise xlog_op_header in item formatting
>       xfs: log ticket region debug is largely useless
>       xfs: pass lv chain length into xlog_write()
>       xfs: introduce xlog_write_single()
>       xfs:_introduce xlog_write_partial()
>       xfs: xlog_write() no longer needs contwr state
>       xfs: xlog_write() doesn't need optype anymore
>       xfs: CIL context doesn't need to count iovecs
>       xfs: use the CIL space used counter for emptiness checks
>       xfs: lift init CIL reservation out of xc_cil_lock
>       xfs: rework per-iclog header CIL reservation
>       xfs: introduce per-cpu CIL tracking structure
>       xfs: implement percpu cil space used calculation
>       xfs: track CIL ticket reservation in percpu structure
>       xfs: convert CIL busy extents to per-cpu
>       xfs: Add order IDs to log items in CIL
>       xfs: convert CIL to unordered per cpu lists
>       xfs: convert log vector chain to use list heads
>       xfs: move CIL ordering to the logvec chain
>       xfs: avoid cil push lock if possible
>       xfs: xlog_sync() manually adjusts grant head space
>       xfs: expanding delayed logging design with background material
> 
>  Documentation/filesystems/xfs-delayed-logging-design.rst |  361 ++++++++++++++++++++++++++----
>  fs/xfs/libxfs/xfs_log_format.h                           |    4 -
>  fs/xfs/libxfs/xfs_types.h                                |    1 +
>  fs/xfs/xfs_bio_io.c                                      |   35 +++
>  fs/xfs/xfs_buf.c                                         |    2 +-
>  fs/xfs/xfs_buf_item.c                                    |   39 ++--
>  fs/xfs/xfs_dquot_item.c                                  |    2 +-
>  fs/xfs/xfs_file.c                                        |   20 +-
>  fs/xfs/xfs_inode.c                                       |   10 +-
>  fs/xfs/xfs_inode_item.c                                  |   18 +-
>  fs/xfs/xfs_inode_item.h                                  |    2 +-
>  fs/xfs/xfs_linux.h                                       |    2 +
>  fs/xfs/xfs_log.c                                         | 1015 +++++++++++++++++++++++++++++++++++++++---------------------------------------------
>  fs/xfs/xfs_log.h                                         |   66 ++----
>  fs/xfs/xfs_log_cil.c                                     |  822 ++++++++++++++++++++++++++++++++++++++++++++++++++------------------
>  fs/xfs/xfs_log_priv.h                                    |  114 +++++-----
>  fs/xfs/xfs_super.c                                       |   13 +-
>  fs/xfs/xfs_super.h                                       |    1 -
>  fs/xfs/xfs_sysfs.c                                       |    1 +
>  fs/xfs/xfs_trace.c                                       |    1 +
>  fs/xfs/xfs_trans.c                                       |   18 +-
>  fs/xfs/xfs_trans.h                                       |    5 +-
>  fs/xfs/xfs_trans_ail.c                                   |   11 +-
>  fs/xfs/xfs_trans_priv.h                                  |    3 +-
>  include/linux/cpuhotplug.h                               |    1 +
>  25 files changed, 1603 insertions(+), 964 deletions(-)
> 
> -- 
> Dave Chinner
> david@fromorbit.com