Pull locking updates from Thomas Gleixner:
"A set of locking fixes and updates:
- Untangle the header spaghetti which causes build failures in
various situations caused by the lockdep additions to seqcount to
validate that the write side critical sections are non-preemptible.
- The seqcount associated lock debug addons which were blocked by the
above fallout.
seqcount writers contrary to seqlock writers must be externally
serialized, which usually happens via locking - except for strict
per CPU seqcounts. As the lock is not part of the seqcount, lockdep
cannot validate that the lock is held.
This new debug mechanism adds the concept of associated locks.
sequence count has now lock type variants and corresponding
initializers which take a pointer to the associated lock used for
writer serialization. If lockdep is enabled the pointer is stored
and write_seqcount_begin() has a lockdep assertion to validate that
the lock is held.
Aside of the type and the initializer no other code changes are
required at the seqcount usage sites. The rest of the seqcount API
is unchanged and determines the type at compile time with the help
of _Generic which is possible now that the minimal GCC version has
been moved up.
Adding this lockdep coverage unearthed a handful of seqcount bugs
which have been addressed already independent of this.
While generally useful this comes with a Trojan Horse twist: On RT
kernels the write side critical section can become preemtible if
the writers are serialized by an associated lock, which leads to
the well known reader preempts writer livelock. RT prevents this by
storing the associated lock pointer independent of lockdep in the
seqcount and changing the reader side to block on the lock when a
reader detects that a writer is in the write side critical section.
- Conversion of seqcount usage sites to associated types and
initializers"
* tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (25 commits)
locking/seqlock, headers: Untangle the spaghetti monster
locking, arch/ia64: Reduce <asm/smp.h> header dependencies by moving XTP bits into the new <asm/xtp.h> header
x86/headers: Remove APIC headers from <asm/smp.h>
seqcount: More consistent seqprop names
seqcount: Compress SEQCNT_LOCKNAME_ZERO()
seqlock: Fold seqcount_LOCKNAME_init() definition
seqlock: Fold seqcount_LOCKNAME_t definition
seqlock: s/__SEQ_LOCKDEP/__SEQ_LOCK/g
hrtimer: Use sequence counter with associated raw spinlock
kvm/eventfd: Use sequence counter with associated spinlock
userfaultfd: Use sequence counter with associated spinlock
NFSv4: Use sequence counter with associated spinlock
iocost: Use sequence counter with associated spinlock
raid5: Use sequence counter with associated spinlock
vfs: Use sequence counter with associated spinlock
timekeeping: Use sequence counter with associated raw spinlock
xfrm: policy: Use sequence counters with associated lock
netfilter: nft_set_rbtree: Use sequence counter with associated rwlock
netfilter: conntrack: Use sequence counter with associated spinlock
sched: tasks: Use sequence counter with associated spinlock
...
Pull block driver updates from Jens Axboe:
- NVMe:
- ZNS support (Aravind, Keith, Matias, Niklas)
- Misc cleanups, optimizations, fixes (Baolin, Chaitanya, David,
Dongli, Max, Sagi)
- null_blk zone capacity support (Aravind)
- MD:
- raid5/6 fixes (ChangSyun)
- Warning fixes (Damien)
- raid5 stripe fixes (Guoqing, Song, Yufen)
- sysfs deadlock fix (Junxiao)
- raid10 deadlock fix (Vitaly)
- struct_size conversions (Gustavo)
- Set of bcache updates/fixes (Coly)
* tag 'for-5.9/drivers-20200803' of git://git.kernel.dk/linux-block: (117 commits)
md/raid5: Allow degraded raid6 to do rmw
md/raid5: Fix Force reconstruct-write io stuck in degraded raid5
raid5: don't duplicate code for different paths in handle_stripe
raid5-cache: hold spinlock instead of mutex in r5c_journal_mode_show
md: print errno in super_written
md/raid5: remove the redundant setting of STRIPE_HANDLE
md: register new md sysfs file 'uuid' read-only
md: fix max sectors calculation for super 1.0
nvme-loop: remove extra variable in create ctrl
nvme-loop: set ctrl state connecting after init
nvme-multipath: do not fall back to __nvme_find_path() for non-optimized paths
nvme-multipath: fix logic for non-optimized paths
nvme-rdma: fix controller reset hang during traffic
nvme-tcp: fix controller reset hang during traffic
nvmet: introduce the passthru Kconfig option
nvmet: introduce the passthru configfs interface
nvmet: Add passthru enable/disable helpers
nvmet: add passthru code to process commands
nvme: export nvme_find_get_ns() and nvme_put_ns()
nvme: introduce nvme_ctrl_get_by_path()
...
Degraded raid6 always do reconstruct-write now. With raid6 xor supported,
we can do rmw in degraded raid6. This patch can reduce many read IOs to
improve performance.
If the failed disk is P, Q or the disk we want to write to, we may need to
do reconstruct-write in max degraded raid6. In this situation we can not
read enough data from handle_stripe_dirtying() so we have to set force_rcw
in handle_stripe_fill() to read all data.
Reviewed-by: Alex Wu <alexwu@synology.com>
Reviewed-by: BingJing Chang <bingjingc@synology.com>
Reviewed-by: Danny Shih <dannyshih@synology.com>
Signed-off-by: ChangSyun Peng <allenpeng@synology.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
In degraded raid5, we need to read parity to do reconstruct-write when
data disks fail. However, we can not read parity from
handle_stripe_dirtying() in force reconstruct-write mode.
Reproducible Steps:
1. Create degraded raid5
mdadm -C /dev/md2 --assume-clean -l5 -n3 /dev/sda2 /dev/sdb2 missing
2. Set rmw_level to 0
echo 0 > /sys/block/md2/md/rmw_level
3. IO to raid5
Now some io may be stuck in raid5. We can use handle_stripe_fill() to read
the parity in this situation.
Cc: <stable@vger.kernel.org> # v4.4+
Reviewed-by: Alex Wu <alexwu@synology.com>
Reviewed-by: BingJing Chang <bingjingc@synology.com>
Reviewed-by: Danny Shih <dannyshih@synology.com>
Signed-off-by: ChangSyun Peng <allenpeng@synology.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
As we can see, R5_LOCKED is set and s.locked is increased whether
R5_ReWrite is set or not, so move it to common path.
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
The flag is already set before compare rcw with rmw, so it is
not necessary to do it again.
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
A sequence counter write side critical section must be protected by some
form of locking to serialize writers. A plain seqcount_t does not
contain the information of which lock must be held when entering a write
side critical section.
Use the new seqcount_spinlock_t data type, which allows to associate a
spinlock with the sequence counter. This enables lockdep to verify that
the spinlock used for writer serialization is held when the write side
critical section is entered.
If lockdep is disabled this lock association is compiled out and has
neither storage size nor runtime overhead.
Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Song Liu <song@kernel.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-20-a.darwish@linutronix.de
We get compilation error on 32-bit architectures (e.g. m68k), as:
ERROR: modpost: "__udivdi3" [drivers/md/raid456.ko] undefined!
Since 'sync_blocks' is defined as u64, use do_div() to fix this error.
Fixes: c911c46c01 ("md/raid456: convert macro STRIPE_* to RAID5_STRIPE_*")
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Adding a new 'stripe_size' sysfs entry to set and show stripe_size.
stripe_size should not be bigger than PAGE_SIZE, and it requires to
be multiple of 4096. We can adjust stripe_size by writing value into
sysfs entry, likely, set stripe_size as 16KB:
echo 16384 > /sys/block/md1/md/stripe_size
Show current stripe_size value:
cat /sys/block/md1/md/stripe_size
For PAGE_SIZE is equal to 4096, 'stripe_size' can just be read.
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
In RAID5, if issued bio size is bigger than stripe_size, it will be
split in the unit of stripe_size and process them one by one. Even
for size less then stripe_size, RAID5 also request data from disk at
least of stripe_size.
Nowdays, stripe_size is equal to the value of PAGE_SIZE. Since filesystem
usually issue bio in the unit of 4KB, there is no problem for PAGE_SIZE
as 4KB. But, for 64KB PAGE_SIZE, bio from filesystem requests 4KB data
while RAID5 issue IO at least stripe_size (64KB) each time. That will
waste resource of disk bandwidth and compute xor.
To avoding the waste, we want to make stripe_size configurable. This
patch just set default stripe_size as 4096. User can also set the value
bigger than 4KB for some special requirements, such as we know the
issued io size is more than 4KB.
To evaluate the new feature, we create raid5 device '/dev/md5' with
4 SSD disk and test it on arm64 machine with 64KB PAGE_SIZE.
1) We format /dev/md5 with mkfs.ext4 and mount ext4 with default
configure on /mnt directory. Then, trying to test it by dbench with
command: dbench -D /mnt -t 1000 10. Result show as:
'stripe_size = 64KB'
Operation Count AvgLat MaxLat
----------------------------------------
NTCreateX 9805011 0.021 64.728
Close 7202525 0.001 0.120
Rename 415213 0.051 44.681
Unlink 1980066 0.079 93.147
Deltree 240 1.793 6.516
Mkdir 120 0.004 0.007
Qpathinfo 8887512 0.007 37.114
Qfileinfo 1557262 0.001 0.030
Qfsinfo 1629582 0.012 0.152
Sfileinfo 798756 0.040 57.641
Find 3436004 0.019 57.782
WriteX 4887239 0.021 57.638
ReadX 15370483 0.005 37.818
LockX 31934 0.003 0.022
UnlockX 31933 0.001 0.021
Flush 687205 13.302 530.088
Throughput 307.799 MB/sec 10 clients 10 procs max_latency=530.091 ms
-------------------------------------------------------
'stripe_size = 4KB'
Operation Count AvgLat MaxLat
----------------------------------------
NTCreateX 11999166 0.021 36.380
Close 8814128 0.001 0.122
Rename 508113 0.051 29.169
Unlink 2423242 0.070 38.141
Deltree 300 1.885 7.155
Mkdir 150 0.004 0.006
Qpathinfo 10875921 0.007 35.485
Qfileinfo 1905837 0.001 0.032
Qfsinfo 1994304 0.012 0.125
Sfileinfo 977450 0.029 26.489
Find 4204952 0.019 9.361
WriteX 5981890 0.019 27.804
ReadX 18809742 0.004 33.491
LockX 39074 0.003 0.025
UnlockX 39074 0.001 0.014
Flush 841022 10.712 458.848
Throughput 376.777 MB/sec 10 clients 10 procs max_latency=458.852 ms
-------------------------------------------------------
It show that setting stripe_size as 4KB has higher thoughput, i.e.
(376.777 vs 307.799) and has smaller latency than that setting as 64KB.
2) We try to evaluate IO throughput for /dev/md5 by fio with config:
[4KB randwrite]
direct=1
numjob=2
iodepth=64
ioengine=libaio
filename=/dev/md5
bs=4KB
rw=randwrite
[64KB write]
direct=1
numjob=2
iodepth=64
ioengine=libaio
filename=/dev/md5
bs=1MB
rw=write
The result as follow:
+ +
| stripe_size(64KB) | stripe_size(4KB)
+----------------------------------------------------+
4KB randwrite | 15MB/s | 100MB/s
+----------------------------------------------------+
1MB write | 1000MB/s | 700MB/s
The result show that when size of io is bigger than 4KB (64KB),
64KB stripe_size has much higher IOPS. But for 4KB randwrite, that
means, size of io issued to device are smaller, 4KB stripe_size
have better performance.
Normally, default value (4096) can get relatively good performance.
But if each issued io is bigger than 4096, setting value more than
4096 may get better performance.
Here, we just set default stripe_size as 4096, and we will try to
support setting different stripe_size by sysfs interface in the
following patch.
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Convert macro STRIPE_SIZE, STRIPE_SECTORS and STRIPE_SHIFT to
RAID5_STRIPE_SIZE(), RAID5_STRIPE_SECTORS() and RAID5_STRIPE_SHIFT().
This patch is prepare for the following adjustable stripe_size.
It will not change any existing functionality.
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
We can't guarntee the batched stripe to be set with STRIPE_HANDLE since
there are lots of functions could set the flag, such as sync_request,
ops_complete_* and end_{read,write}_request etc.
Also clear_batch_ready called in handle_stripe ensures the batched list
can't continue to be handled by handle_stripe.
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
We tried to only put the head sh of batch list to handle_list, then the
handle_stripe doesn't handle other members in the batch list. However,
we still got the calltrace in break_stripe_batch_list.
[593764.644269] stripe state: 2003
kernel: [593764.644299] ------------[ cut here ]------------
kernel: [593764.644308] WARNING: CPU: 12 PID: 856 at drivers/md/raid5.c:4625 break_stripe_batch_list+0x203/0x240 [raid456]
[...]
kernel: [593764.644363] Call Trace:
kernel: [593764.644370] handle_stripe+0x907/0x20c0 [raid456]
kernel: [593764.644376] ? __wake_up_common_lock+0x89/0xc0
kernel: [593764.644379] handle_active_stripes.isra.57+0x35f/0x570 [raid456]
kernel: [593764.644382] ? raid5_wakeup_stripe_thread+0x96/0x1f0 [raid456]
kernel: [593764.644385] raid5d+0x480/0x6a0 [raid456]
kernel: [593764.644390] ? md_thread+0x11f/0x160
kernel: [593764.644392] md_thread+0x11f/0x160
kernel: [593764.644394] ? wait_woken+0x80/0x80
kernel: [593764.644396] kthread+0xfc/0x130
kernel: [593764.644398] ? find_pers+0x70/0x70
kernel: [593764.644399] ? kthread_create_on_node+0x70/0x70
kernel: [593764.644401] ret_from_fork+0x1f/0x30
As we can see, the stripe was set with STRIPE_ACTIVE and STRIPE_HANDLE,
and only handle_stripe could set those flags then return. And since the
stipe was already in the batch list, we need to return earlier before
set the two flags.
And after dig a little about git history especially commit 3664847d95
("md/raid5: fix a race condition in stripe batch"), it seems the batched
stipe still could be handled by handle_stipe, then handle_stipe needs to
return earlier if clear_batch_ready to return true.
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Remove the if statement around the calls to sysfs_link_rdev() to avoid
the compilation warning "suggest braces around empty body in an ‘if’
statement" when compiling with W=1.
Also fix function description comments to avoid kdoc format warnings.
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
The following deadlock was captured. The first process is holding 'kernfs_mutex'
and hung by io. The io was staging in 'r1conf.pending_bio_list' of raid1 device,
this pending bio list would be flushed by second process 'md127_raid1', but
it was hung by 'kernfs_mutex'. Using sysfs_notify_dirent_safe() to replace
sysfs_notify() can fix it. There were other sysfs_notify() invoked from io
path, removed all of them.
PID: 40430 TASK: ffff8ee9c8c65c40 CPU: 29 COMMAND: "probe_file"
#0 [ffffb87c4df37260] __schedule at ffffffff9a8678ec
#1 [ffffb87c4df372f8] schedule at ffffffff9a867f06
#2 [ffffb87c4df37310] io_schedule at ffffffff9a0c73e6
#3 [ffffb87c4df37328] __dta___xfs_iunpin_wait_3443 at ffffffffc03a4057 [xfs]
#4 [ffffb87c4df373a0] xfs_iunpin_wait at ffffffffc03a6c79 [xfs]
#5 [ffffb87c4df373b0] __dta_xfs_reclaim_inode_3357 at ffffffffc039a46c [xfs]
#6 [ffffb87c4df37400] xfs_reclaim_inodes_ag at ffffffffc039a8b6 [xfs]
#7 [ffffb87c4df37590] xfs_reclaim_inodes_nr at ffffffffc039bb33 [xfs]
#8 [ffffb87c4df375b0] xfs_fs_free_cached_objects at ffffffffc03af0e9 [xfs]
#9 [ffffb87c4df375c0] super_cache_scan at ffffffff9a287ec7
#10 [ffffb87c4df37618] shrink_slab at ffffffff9a1efd93
#11 [ffffb87c4df37700] shrink_node at ffffffff9a1f5968
#12 [ffffb87c4df37788] do_try_to_free_pages at ffffffff9a1f5ea2
#13 [ffffb87c4df377f0] try_to_free_mem_cgroup_pages at ffffffff9a1f6445
#14 [ffffb87c4df37880] try_charge at ffffffff9a26cc5f
#15 [ffffb87c4df37920] memcg_kmem_charge_memcg at ffffffff9a270f6a
#16 [ffffb87c4df37958] new_slab at ffffffff9a251430
#17 [ffffb87c4df379c0] ___slab_alloc at ffffffff9a251c85
#18 [ffffb87c4df37a80] __slab_alloc at ffffffff9a25635d
#19 [ffffb87c4df37ac0] kmem_cache_alloc at ffffffff9a251f89
#20 [ffffb87c4df37b00] alloc_inode at ffffffff9a2a2b10
#21 [ffffb87c4df37b20] iget_locked at ffffffff9a2a4854
#22 [ffffb87c4df37b60] kernfs_get_inode at ffffffff9a311377
#23 [ffffb87c4df37b80] kernfs_iop_lookup at ffffffff9a311e2b
#24 [ffffb87c4df37ba8] lookup_slow at ffffffff9a290118
#25 [ffffb87c4df37c10] walk_component at ffffffff9a291e83
#26 [ffffb87c4df37c78] path_lookupat at ffffffff9a293619
#27 [ffffb87c4df37cd8] filename_lookup at ffffffff9a2953af
#28 [ffffb87c4df37de8] user_path_at_empty at ffffffff9a295566
#29 [ffffb87c4df37e10] vfs_statx at ffffffff9a289787
#30 [ffffb87c4df37e70] SYSC_newlstat at ffffffff9a289d5d
#31 [ffffb87c4df37f18] sys_newlstat at ffffffff9a28a60e
#32 [ffffb87c4df37f28] do_syscall_64 at ffffffff9a003949
#33 [ffffb87c4df37f50] entry_SYSCALL_64_after_hwframe at ffffffff9aa001ad
RIP: 00007f617a5f2905 RSP: 00007f607334f838 RFLAGS: 00000246
RAX: ffffffffffffffda RBX: 00007f6064044b20 RCX: 00007f617a5f2905
RDX: 00007f6064044b20 RSI: 00007f6064044b20 RDI: 00007f6064005890
RBP: 00007f6064044aa0 R8: 0000000000000030 R9: 000000000000011c
R10: 0000000000000013 R11: 0000000000000246 R12: 00007f606417e6d0
R13: 00007f6064044aa0 R14: 00007f6064044b10 R15: 00000000ffffffff
ORIG_RAX: 0000000000000006 CS: 0033 SS: 002b
PID: 927 TASK: ffff8f15ac5dbd80 CPU: 42 COMMAND: "md127_raid1"
#0 [ffffb87c4df07b28] __schedule at ffffffff9a8678ec
#1 [ffffb87c4df07bc0] schedule at ffffffff9a867f06
#2 [ffffb87c4df07bd8] schedule_preempt_disabled at ffffffff9a86825e
#3 [ffffb87c4df07be8] __mutex_lock at ffffffff9a869bcc
#4 [ffffb87c4df07ca0] __mutex_lock_slowpath at ffffffff9a86a013
#5 [ffffb87c4df07cb0] mutex_lock at ffffffff9a86a04f
#6 [ffffb87c4df07cc8] kernfs_find_and_get_ns at ffffffff9a311d83
#7 [ffffb87c4df07cf0] sysfs_notify at ffffffff9a314b3a
#8 [ffffb87c4df07d18] md_update_sb at ffffffff9a688696
#9 [ffffb87c4df07d98] md_update_sb at ffffffff9a6886d5
#10 [ffffb87c4df07da8] md_check_recovery at ffffffff9a68ad9c
#11 [ffffb87c4df07dd0] raid1d at ffffffffc01f0375 [raid1]
#12 [ffffb87c4df07ea0] md_thread at ffffffff9a680348
#13 [ffffb87c4df07f08] kthread at ffffffff9a0b8005
#14 [ffffb87c4df07f50] ret_from_fork at ffffffff9aa00344
Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Except for pktdvd, the only places setting congested bits are file
systems that allocate their own backing_dev_info structures. And
pktdvd is a deprecated driver that isn't useful in stack setup
either. So remove the dead congested_fn stacking infrastructure.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Song Liu <song@kernel.org>
Acked-by: David Sterba <dsterba@suse.com>
[axboe: fixup unused variables in bcache/request.c]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
generic_make_request has always been very confusingly misnamed, so rename
it to submit_bio_noacct to make it clear that it is submit_bio minus
accounting and a few checks.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Code comments of scribble_alloc() is outdated for a while. This patch
update the comments in function header for the new parameter list.
Suggested-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Song Liu <songliubraving@fb.com>
Using GFP_NOIO flag to call scribble_alloc() from resize_chunk() does
not have the expected behavior. kvmalloc_array() inside scribble_alloc()
which receives the GFP_NOIO flag will eventually call kmalloc_node() to
allocate physically continuous pages.
Now we have memalloc scope APIs in mddev_suspend()/mddev_resume() to
prevent memory reclaim I/Os during raid array suspend context, calling
to kvmalloc_array() with GFP_KERNEL flag may avoid deadlock of recursive
I/O as expected.
This patch removes the useless gfp flags from parameters list of
scribble_alloc(), and call kvmalloc_array() with GFP_KERNEL flag. The
incorrect GFP_NOIO flag does not exist anymore.
Fixes: b330e6a49d ("md: convert to kvmalloc")
Suggested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Song Liu <songliubraving@fb.com>
We can use "cnt" directly to update conf->worker_cnt_per_group
if alloc_thread_groups returns 0.
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
With commit 6ce220dd2f ("raid5: don't set
STRIPE_HANDLE to stripe which is in batch list"), we don't want to set
STRIPE_HANDLE flag for sh which is already in batch list.
However, the stripe which is the head of batch list should set this flag,
otherwise panic could happen inside init_stripe at BUG_ON(sh->batch_head),
it is reproducible with raid5 on top of nvdimm devices per Xiao oberserved.
Thanks for Xiao's effort to verify the change.
Fixes: 6ce220dd2f ("raid5: don't set STRIPE_HANDLE to stripe which is in batch list")
Reported-by: Xiao Ni <xni@redhat.com>
Tested-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
As it is consistent with prefixes of other write life time hints.
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
