The function bfq_setup_merge prepares the merging between two
bfq_queues, say bfqq and new_bfqq. To this goal, it assigns
bfqq->new_bfqq = new_bfqq. Then, each time some I/O for bfqq arrives,
the process that generated that I/O is disassociated from bfqq and
associated with new_bfqq (merging is actually a redirection). In this
respect, bfq_setup_merge increases new_bfqq->ref in advance, adding
the number of processes that are expected to be associated with
new_bfqq.
Unfortunately, the stable-merging mechanism interferes with this
setup. After bfqq->new_bfqq has been set by bfq_setup_merge, and
before all the expected processes have been associated with
bfqq->new_bfqq, bfqq may happen to be stably merged with a different
queue than the current bfqq->new_bfqq. In this case, bfqq->new_bfqq
gets changed. So, some of the processes that have been already
accounted for in the ref counter of the previous new_bfqq will not be
associated with that queue. This creates an unbalance, because those
references will never be decremented.
This commit fixes this issue by reestablishing the previous, natural
behaviour: once bfqq->new_bfqq has been set, it will not be changed
until all expected redirections have occurred.
Signed-off-by: Davide Zini <davidezini2@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20210802141352.74353-2-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Replace the magic lookup through the kobject tree with an explicit
backpointer, given that the device model links are set up and torn
down at times when I/O is still possible, leading to potential
NULL or invalid pointer dereferences.
Fixes: edb0872f44 ("block: move the bdi from the request_queue to the gendisk")
Reported-by: syzbot <syzbot+aa0801b6b32dca9dda82@syzkaller.appspotmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Sven Schnelle <svens@linux.ibm.com>
Link: https://lore.kernel.org/r/20210816134624.GA24234@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The default IO priority is the best effort (BE) class with the
normal priority level IOPRIO_NORM (4). However, get_task_ioprio()
returns IOPRIO_CLASS_NONE/IOPRIO_NORM as the default priority and
get_current_ioprio() returns IOPRIO_CLASS_NONE/0. Let's be consistent
with the defined default and have both of these functions return the
default priority IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM) when
the user did not define another default IO priority for the task.
In include/uapi/linux/ioprio.h, introduce the IOPRIO_BE_NORM macro as
an alias to IOPRIO_NORM to clarify that this default level applies to
the BE priotity class. In include/linux/ioprio.h, define the macro
IOPRIO_DEFAULT as IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_BE_NORM)
and use this new macro when setting a priority to the default.
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Link: https://lore.kernel.org/r/20210811033702.368488-7-damien.lemoal@wdc.com
[axboe: drop unnecessary lightnvm change]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The BFQ scheduler and ioprio_check_cap() both assume that the RT
priority class (IOPRIO_CLASS_RT) can have up to 8 different priority
levels, similarly to the BE class (IOPRIO_CLASS_iBE). This is
controlled using the IOPRIO_BE_NR macro , which is badly named as the
number of levels also applies to the RT class.
Introduce the class independent IOPRIO_NR_LEVELS macro, defined to 8,
to make things clear. Keep the old IOPRIO_BE_NR macro definition as an
alias for IOPRIO_NR_LEVELS.
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Link: https://lore.kernel.org/r/20210811033702.368488-6-damien.lemoal@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
For a request that has a priority level equal to or larger than
IOPRIO_BE_NR, bfq_set_next_ioprio_data() prints a critical warning but
defaults to setting the request new_ioprio field to IOPRIO_BE_NR. This
is not consistent with the warning and the allowed values for priority
levels. Fix this by setting the request new_ioprio field to
IOPRIO_BE_NR - 1, the lowest priority level allowed.
Cc: <stable@vger.kernel.org>
Fixes: aee69d78de ("block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler")
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20210811033702.368488-2-damien.lemoal@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When merging one bio to request, if they are discard IO and the queue
supports multi-range discard, we need to return ELEVATOR_DISCARD_MERGE
because both block core and related drivers(nvme, virtio-blk) doesn't
handle mixed discard io merge(traditional IO merge together with
discard merge) well.
Fix the issue by returning ELEVATOR_DISCARD_MERGE in this situation,
so both blk-mq and drivers just need to handle multi-range discard.
Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Fixes: 2705dfb209 ("block: fix discard request merge")
Link: https://lore.kernel.org/r/20210729034226.1591070-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The backing device information only makes sense for file system I/O,
and thus belongs into the gendisk and not the lower level request_queue
structure. Move it there.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20210809141744.1203023-5-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Lockdep complains about lock inversion between ioc->lock and bfqd->lock:
bfqd -> ioc:
put_io_context+0x33/0x90 -> ioc->lock grabbed
blk_mq_free_request+0x51/0x140
blk_put_request+0xe/0x10
blk_attempt_req_merge+0x1d/0x30
elv_attempt_insert_merge+0x56/0xa0
blk_mq_sched_try_insert_merge+0x4b/0x60
bfq_insert_requests+0x9e/0x18c0 -> bfqd->lock grabbed
blk_mq_sched_insert_requests+0xd6/0x2b0
blk_mq_flush_plug_list+0x154/0x280
blk_finish_plug+0x40/0x60
ext4_writepages+0x696/0x1320
do_writepages+0x1c/0x80
__filemap_fdatawrite_range+0xd7/0x120
sync_file_range+0xac/0xf0
ioc->bfqd:
bfq_exit_icq+0xa3/0xe0 -> bfqd->lock grabbed
put_io_context_active+0x78/0xb0 -> ioc->lock grabbed
exit_io_context+0x48/0x50
do_exit+0x7e9/0xdd0
do_group_exit+0x54/0xc0
To avoid this inversion we change blk_mq_sched_try_insert_merge() to not
free the merged request but rather leave that upto the caller similarly
to blk_mq_sched_try_merge(). And in bfq_insert_requests() we make sure
to free all the merged requests after dropping bfqd->lock.
Fixes: aee69d78de ("block, bfq: introduce the BFQ-v0 I/O scheduler as an extra scheduler")
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210623093634.27879-3-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Currently, bfq does very little in bfq_requests_merged() and handles all
the request cleanup in bfq_finish_requeue_request() called from
blk_mq_free_request(). That is currently safe only because
blk_mq_free_request() is called shortly after bfq_requests_merged()
while bfqd->lock is still held. However to fix a lock inversion between
bfqd->lock and ioc->lock, we need to call blk_mq_free_request() after
dropping bfqd->lock. That would mean that already merged request could
be seen by other processes inside bfq queues and possibly dispatched to
the device which is wrong. So move cleanup of the request from
bfq_finish_requeue_request() to bfq_requests_merged().
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210623093634.27879-2-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Commit 85686d0dc1 ("block, bfq: keep shared queues out of the waker
mechanism") leaves shared bfq_queues out of the waker-detection
mechanism. It attains this goal by not updating the pointer
last_completed_rq_bfqq, if the last request completed belongs to a
shared bfq_queue (so that the pointer will not point to the shared
bfq_queue).
Yet this has a side effect: the pointer last_completed_rq_bfqq keeps
pointing, deceptively, to a bfq_queue that actually is not the last
one to have had a request completed. As a consequence, such a
bfq_queue may deceptively be considered as a waker of some bfq_queue,
even of some shared bfq_queue.
To address this issue, reset last_completed_rq_bfqq if the last
request completed belongs to a shared queue.
Fixes: 85686d0dc1 ("block, bfq: keep shared queues out of the waker mechanism")
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20210619140948.98712-8-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Consider two bfq_queues, say Q1 and Q2, with Q2 empty. If a request of
Q1 gets completed shortly before a new request arrives for Q2, then
BFQ flags Q1 as a candidate waker for Q2. Yet, the arrival of this new
request may have a different cause, in the following case. If also Q2
has requests in flight while waiting for the arrival of a new request,
then the completion of its own requests may be the actual cause of the
awakening of the process that sends I/O to Q2. So Q1 may be flagged
wrongly as a candidate waker.
This commit avoids this deceptive flagging, by disabling
candidate-waker flagging for Q2, if Q2 has in-flight I/O.
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20210619140948.98712-7-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Since commit 430a67f9d6 ("block, bfq: merge bursts of newly-created
queues"), BFQ may schedule a merge between a newly created sync
bfq_queue, say Q2, and the last sync bfq_queue created, say Q1. To this
goal, BFQ stores the address of Q1 in the field bic->stable_merge_bfqq
of the bic associated with Q2. So, when the time for the possible merge
arrives, BFQ knows which bfq_queue to merge Q2 with. In particular,
BFQ checks for possible merges on request arrivals.
Yet the same bic may also be associated with an async bfq_queue, say
Q3. So, if a request for Q3 arrives, then the above check may happen
to be executed while the bfq_queue at hand is Q3, instead of Q2. In
this case, Q1 happens to be merged with an async bfq_queue. This is
not only a conceptual mistake, because async queues are to be kept out
of queue merging, but also a bug that leads to inconsistent states.
This commits simply filters async queues out of delayed merges.
Fixes: 430a67f9d6 ("block, bfq: merge bursts of newly-created queues")
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20210619140948.98712-6-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
One of the methods with which bfq boosts throughput is by merging queues.
One of the merging variants in bfq is the stable merge.
This mechanism is activated between two queues only if they are created
within a certain maximum time T1 from each other.
Merging can happen soon or be delayed. In the second case, before
merging, bfq needs to evaluate a throughput-boost parameter that
indicates whether the queue generates a high throughput is served alone.
Merging occurs when this throughput-boost is not high enough.
In particular, this parameter is evaluated and late merging may occur
only after at least a time T2 from the creation of the queue.
Currently T1 and T2 are set to 180ms and 200ms, respectively.
In this way the merging mechanism rarely occurs because time is not
enough. This results in a noticeable lowering of the overall throughput
with some workloads (see the example below).
This commit introduces two constants bfq_activation_stable_merging and
bfq_late_stable_merging in order to increase the duration of T1 and T2.
Both the stable merging activation time and the late merging
time are set to 600ms. This value has been experimentally evaluated
using sqlite benchmark in the Phoronix Test Suite on a HDD.
The duration of the benchmark before this fix was 111.02s, while now
it has reached 97.02s, a better result than that of all the other
schedulers.
Signed-off-by: Pietro Pedroni <pedroni.pietro.96@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20210619140948.98712-5-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Since commit 430a67f9d6 ("block, bfq: merge bursts of newly-created
queues"), BFQ may schedule a merge between a newly created sync
bfq_queue and the last sync bfq_queue created. Such a merging is not
performed immediately, because BFQ needs first to find out whether the
newly created queue actually reaches a higher throughput if not merged
at all (and in that case BFQ will not perform any stable merging). To
check that, a little time must be waited after the creation of the new
queue, so that some I/O can flow in the queue, and statistics on such
I/O can be computed.
Yet, to evaluate the above waiting time, the last split time is
considered as start time, instead of the creation time of the
queue. This is a mistake, because considering the split time is
correct only in the following scenario.
The queue undergoes a non-stable merges on the arrival of its very
first I/O request, due to close I/O with some other queue. While the
queue is merged for close I/O, stable merging is not considered. Yet
the queue may then happen to be split, if the close I/O finishes (or
happens to be a false positive). From this time on, the queue can
again be considered for stable merging. But, again, a little time must
elapse, to let some new I/O flow in the queue and to get updated
statistics. To wait for this time, the split time is to be taken into
account.
Yet, if the queue does not undergo a non-stable merge on the arrival
of its very first request, then BFQ immediately checks whether the
stable merge is to be performed. It happens because the split time for
a queue is initialized to minus infinity when the queue is created.
This commit fixes this mistake by adding the missing condition. Now
the check for delayed stable-merge is performed after a little time is
elapsed not only from the last queue split time, but also from the
creation time of the queue.
Fixes: 430a67f9d6 ("block, bfq: merge bursts of newly-created queues")
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20210619140948.98712-4-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When attempting to schedule a merge of a given bfq_queue with the currently
in-service bfq_queue or with a cooperating bfq_queue among the scheduled
bfq_queues, delayed stable merge is checked for rotational or non-queueing
devs. For this stable merge to be performed, some conditions must be met.
If the current bfq_queue underwent some split from some merged bfq_queue,
one of these conditions is that two hundred milliseconds must elapse from
split, otherwise this condition is always met.
Unfortunately, by mistake, time_is_after_jiffies() was written instead of
time_is_before_jiffies() for this check, verifying that less than two
hundred milliseconds have elapsed instead of verifying that at least two
hundred milliseconds have elapsed.
Fix this issue by replacing time_is_after_jiffies() with
time_is_before_jiffies().
Signed-off-by: Luca Mariotti <mariottiluca1@hotmail.it>
Signed-off-by: Paolo Valente <paolo.valente@unimore.it>
Signed-off-by: Pietro Pedroni <pedroni.pietro.96@gmail.com>
Link: https://lore.kernel.org/r/20210619140948.98712-3-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Merged bfq_queues are kept out of weight-raising (low-latency)
mechanisms. The reason is that these queues are usually created for
non-interactive and non-soft-real-time tasks. Yet this is not the case
for stably-merged queues. These queues are merged just because they
are created shortly after each other. So they may easily serve the I/O
of an interactive or soft-real time application, if the application
happens to spawn multiple processes.
To address this issue, this commits lets also stably-merged queued
enjoy weight raising.
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20210619140948.98712-2-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
BFQ may merge a new bfq_queue, stably, with the last bfq_queue
created. In particular, BFQ first waits a little bit for some I/O to
flow inside the new queue, say Q2, if this is needed to understand
whether it is better or worse to merge Q2 with the last queue created,
say Q1. This delayed stable merge is performed by assigning
bic->stable_merge_bfqq = Q1, for the bic associated with Q1.
Yet, while waiting for some I/O to flow in Q2, a non-stable queue
merge of Q2 with Q1 may happen, causing the bic previously associated
with Q2 to be associated with exactly Q1 (bic->bfqq = Q1). After that,
Q2 and Q1 may happen to be split, and, in the split, Q1 may happen to
be recycled as a non-shared bfq_queue. In that case, Q1 may then
happen to undergo a stable merge with the bfq_queue pointed by
bic->stable_merge_bfqq. Yet bic->stable_merge_bfqq still points to
Q1. So Q1 would be merged with itself.
This commit fixes this error by intercepting this situation, and
canceling the schedule of the stable merge.
Fixes: 430a67f9d6 ("block, bfq: merge bursts of newly-created queues")
Signed-off-by: Pietro Pedroni <pedroni.pietro.96@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20210512094352.85545-2-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
__blk_mq_sched_bio_merge() gets the ctx and hctx for the current CPU and
passes the hctx to ->bio_merge(). kyber_bio_merge() then gets the ctx
for the current CPU again and uses that to get the corresponding Kyber
context in the passed hctx. However, the thread may be preempted between
the two calls to blk_mq_get_ctx(), and the ctx returned the second time
may no longer correspond to the passed hctx. This "works" accidentally
most of the time, but it can cause us to read garbage if the second ctx
came from an hctx with more ctx's than the first one (i.e., if
ctx->index_hw[hctx->type] > hctx->nr_ctx).
This manifested as this UBSAN array index out of bounds error reported
by Jakub:
UBSAN: array-index-out-of-bounds in ../kernel/locking/qspinlock.c:130:9
index 13106 is out of range for type 'long unsigned int [128]'
Call Trace:
dump_stack+0xa4/0xe5
ubsan_epilogue+0x5/0x40
__ubsan_handle_out_of_bounds.cold.13+0x2a/0x34
queued_spin_lock_slowpath+0x476/0x480
do_raw_spin_lock+0x1c2/0x1d0
kyber_bio_merge+0x112/0x180
blk_mq_submit_bio+0x1f5/0x1100
submit_bio_noacct+0x7b0/0x870
submit_bio+0xc2/0x3a0
btrfs_map_bio+0x4f0/0x9d0
btrfs_submit_data_bio+0x24e/0x310
submit_one_bio+0x7f/0xb0
submit_extent_page+0xc4/0x440
__extent_writepage_io+0x2b8/0x5e0
__extent_writepage+0x28d/0x6e0
extent_write_cache_pages+0x4d7/0x7a0
extent_writepages+0xa2/0x110
do_writepages+0x8f/0x180
__writeback_single_inode+0x99/0x7f0
writeback_sb_inodes+0x34e/0x790
__writeback_inodes_wb+0x9e/0x120
wb_writeback+0x4d2/0x660
wb_workfn+0x64d/0xa10
process_one_work+0x53a/0xa80
worker_thread+0x69/0x5b0
kthread+0x20b/0x240
ret_from_fork+0x1f/0x30
Only Kyber uses the hctx, so fix it by passing the request_queue to
->bio_merge() instead. BFQ and mq-deadline just use that, and Kyber can
map the queues itself to avoid the mismatch.
Fixes: a6088845c2 ("block: kyber: make kyber more friendly with merging")
Reported-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Link: https://lore.kernel.org/r/c7598605401a48d5cfeadebb678abd10af22b83f.1620691329.git.osandov@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Since commit 01e99aeca3 'blk-mq: insert passthrough request into
hctx->dispatch directly', passthrough request should not appear in
IO-scheduler any more, so blk_rq_is_passthrough checking in addon IO
schedulers is redundant.
(Notes: this patch passes generic IO load test with hdds under SAS
controller and hdds under AHCI controller but obviously not covers all.
Not sure if passthrough request can still escape into IO scheduler from
blk_mq_sched_insert_requests, which is used by blk_mq_flush_plug_list and
has lots of indirect callers.)
Signed-off-by: Lin Feng <linf@wangsu.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Many throughput-sensitive workloads are made of several parallel I/O
flows, with all flows generated by the same application, or more
generically by the same task (e.g., system boot). The most
counterproductive action with these workloads is plugging I/O dispatch
when one of the bfq_queues associated with these flows remains
temporarily empty.
To avoid this plugging, BFQ has been using a burst-handling mechanism
for years now. This mechanism has proven effective for throughput, and
not detrimental for service guarantees. This commit pushes this
mechanism a little bit further, basing on the following two facts.
First, all the I/O flows of a the same application or task contribute
to the execution/completion of that common application or task. So the
performance figures that matter are total throughput of the flows and
task-wide I/O latency. In particular, these flows do not need to be
protected from each other, in terms of individual bandwidth or
latency.
Second, the above fact holds regardless of the number of flows.
Putting these two facts together, this commits merges stably the
bfq_queues associated with these I/O flows, i.e., with the processes
that generate these IO/ flows, regardless of how many the involved
processes are.
To decide whether a set of bfq_queues is actually associated with the
I/O flows of a common application or task, and to merge these queues
stably, this commit operates as follows: given a bfq_queue, say Q2,
currently being created, and the last bfq_queue, say Q1, created
before Q2, Q2 is merged stably with Q1 if
- very little time has elapsed since when Q1 was created
- Q2 has the same ioprio as Q1
- Q2 belongs to the same group as Q1
Merging bfq_queues also reduces scheduling overhead. A fio test with
ten random readers on /dev/nullb shows a throughput boost of 40%, with
a quadcore. Since BFQ's execution time amounts to ~50% of the total
per-request processing time, the above throughput boost implies that
BFQ's overhead is reduced by more than 50%.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Link: https://lore.kernel.org/r/20210304174627.161-7-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Shared queues are likely to receive I/O at a high rate. This may
deceptively let them be considered as wakers of other queues. But a
false waker will unjustly steal bandwidth to its supposedly woken
queue. So considering also shared queues in the waking mechanism may
cause more control troubles than throughput benefits. This commit
keeps shared queues out of the waker-detection mechanism.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Link: https://lore.kernel.org/r/20210304174627.161-6-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When the io_latency heuristic is off, bfq_queues must not start to be
weight-raised. Unfortunately, by mistake, this may happen when the
state of a previously weight-raised bfq_queue is resumed after a queue
split. This commit fixes this error.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Link: https://lore.kernel.org/r/20210304174627.161-5-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Consider a bfq_queue bfqq that is about to be merged with another
bfq_queue new_bfqq. The processes associated with bfqq are cooperators
of the processes associated with new_bfqq. So, if bfqq has a waker,
then it is reasonable (and beneficial for throughput) to assume that
all these processes will be happy to let bfqq's waker freely inject
I/O when they have no I/O. So this commit makes new_bfqq inherit
bfqq's waker.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Link: https://lore.kernel.org/r/20210304174627.161-4-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Consider a new I/O request that arrives for a bfq_queue bfqq. If, when
this happens, the only active bfq_queues are bfqq and either its waker
bfq_queue or one of its woken bfq_queues, then there is no point in
queueing this new I/O request in bfqq for service. In fact, the
in-service queue and bfqq agree on serving this new I/O request as
soon as possible. So this commit puts this new I/O request directly
into the dispatch list.
Tested-by: Jan Kara <jack@suse.cz>
Acked-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Link: https://lore.kernel.org/r/20210304174627.161-3-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Suppose that I/O dispatch is plugged, to wait for new I/O for the
in-service bfq-queue, say bfqq. Suppose then that there is a further
bfq_queue woken by bfqq, and that this woken queue has pending I/O. A
woken queue does not steal bandwidth from bfqq, because it remains
soon without I/O if bfqq is not served. So there is virtually no risk
of loss of bandwidth for bfqq if this woken queue has I/O dispatched
while bfqq is waiting for new I/O. In contrast, this extra I/O
injection boosts throughput. This commit performs this extra
injection.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Link: https://lore.kernel.org/r/20210304174627.161-2-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Correct the comments since bfq_fifo_expire[0] is for async request,
while bfq_fifo_expire[1] is for sync request.
Also update docs, according the source code, the default
fifo_expire_async is 250ms, and fifo_expire_sync is 125ms.
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Get rid of the wrapper for trace_block_rq_insert() and call the function
directly.
Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Merge tag 'for-5.12/block-2021-02-17' of git://git.kernel.dk/linux-block
Pull core block updates from Jens Axboe:
"Another nice round of removing more code than what is added, mostly
due to Christoph's relentless pursuit of tech debt removal/cleanups.
This pull request contains:
- Two series of BFQ improvements (Paolo, Jan, Jia)
- Block iov_iter improvements (Pavel)
- bsg error path fix (Pan)
- blk-mq scheduler improvements (Jan)
- -EBUSY discard fix (Jan)
- bvec allocation improvements (Ming, Christoph)
- bio allocation and init improvements (Christoph)
- Store bdev pointer in bio instead of gendisk + partno (Christoph)
- Block trace point cleanups (Christoph)
- hard read-only vs read-only split (Christoph)
- Block based swap cleanups (Christoph)
- Zoned write granularity support (Damien)
- Various fixes/tweaks (Chunguang, Guoqing, Lei, Lukas, Huhai)"
* tag 'for-5.12/block-2021-02-17' of git://git.kernel.dk/linux-block: (104 commits)
mm: simplify swapdev_block
sd_zbc: clear zone resources for non-zoned case
block: introduce blk_queue_clear_zone_settings()
zonefs: use zone write granularity as block size
block: introduce zone_write_granularity limit
block: use blk_queue_set_zoned in add_partition()
nullb: use blk_queue_set_zoned() to setup zoned devices
nvme: cleanup zone information initialization
block: document zone_append_max_bytes attribute
block: use bi_max_vecs to find the bvec pool
md/raid10: remove dead code in reshape_request
block: mark the bio as cloned in bio_iov_bvec_set
block: set BIO_NO_PAGE_REF in bio_iov_bvec_set
block: remove a layer of indentation in bio_iov_iter_get_pages
block: turn the nr_iovecs argument to bio_alloc* into an unsigned short
block: remove the 1 and 4 vec bvec_slabs entries
block: streamline bvec_alloc
block: factor out a bvec_alloc_gfp helper
block: move struct biovec_slab to bio.c
block: reuse BIO_INLINE_VECS for integrity bvecs
...
This reverts commit 6d4d273588.
bfq.limit_depth passes word_depths[] as shallow_depth down to sbitmap core
sbitmap_get_shallow, which uses just the number to limit the scan depth of
each bitmap word, formula:
scan_percentage_for_each_word = shallow_depth / (1 << sbimap->shift) * 100%
That means the comments's percentiles 50%, 75%, 18%, 37% of bfq are correct.
But after commit patch 'bfq: Fix computation of shallow depth', we use
sbitmap.depth instead, as a example in following case:
sbitmap.depth = 256, map_nr = 4, shift = 6; sbitmap_word.depth = 64.
The resulsts of computed bfqd->word_depths[] are {128, 192, 48, 96}, and
three of the numbers exceed core dirver's 'sbitmap_word.depth=64' limit
nothing.
Signed-off-by: Lin Feng <linf@wangsu.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Currently whenever bfq queue has a request queued we add now -
last_completion_time to the think time statistics. This is however
misleading in case the process is able to submit several requests in
parallel because e.g. if the queue has request completed at time T0 and
then queues new requests at times T1, T2, then we will add T1-T0 and
T2-T0 to think time statistics which just doesn't make any sence (the
queue's think time is penalized by the queue being able to submit more
IO). So add to think time statistics only time intervals when the queue
had no IO pending.
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
[axboe: fix whitespace on empty line]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Use local variable 'ttime' instead of dereferencing bfqq.
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
bfq_setup_cooperator() uses bfqd->in_serv_last_pos so detect whether it
makes sense to merge current bfq queue with the in-service queue.
However if the in-service queue is freshly scheduled and didn't dispatch
any requests yet, bfqd->in_serv_last_pos is stale and contains value
from the previously scheduled bfq queue which can thus result in a bogus
decision that the two queues should be merged. This bug can be observed
for example with the following fio jobfile:
[global]
direct=0
ioengine=sync
invalidate=1
size=1g
rw=read
[reader]
numjobs=4
directory=/mnt
where the 4 processes will end up in the one shared bfq queue although
they do IO to physically very distant files (for some reason I was able to
observe this only with slice_idle=1ms setting).
Fix the problem by invalidating bfqd->in_serv_last_pos when switching
in-service queue.
Fixes: 058fdecc6d ("block, bfq: fix in-service-queue check for queue merging")
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
It's only used in the same file, mark is appropriately static.
Fixes: 71217df39d ("block, bfq: make waker-queue detection more robust")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
In the presence of many parallel I/O flows, the detection of waker
bfq_queues suffers from false positives. This commits addresses this
issue by making the filtering of actual wakers more selective. In more
detail, a candidate waker must be found to meet waker requirements
three times before being promoted to actual waker.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
To prevent injection information from being lost on bfq_queue merging,
also the amount of service that a bfq_queue receives must be saved and
restored when the bfq_queue is merged and split, respectively.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
To prevent weight-raising information from being lost on bfq_queue merging,
also the amount of service that a bfq_queue receives must be saved and
restored when the bfq_queue is merged and split, respectively.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
A bfq_queue may happen to be deemed as soft real-time while it is
still enjoying interactive weight-raising. If this happens because of
a false positive, then the bfq_queue is likely to loose its soft
real-time status soon. Upon losing such a status, the bfq_queue must
get back its interactive weight-raising, if its interactive period is
not over yet. But this case is not handled. This commit corrects this
error.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Upon an I/O-dispatch attempt, BFQ may detect that it was better to
plug I/O dispatch, and to wait for a new request to arrive for the
currently in-service queue. But the arrival of a new request for an
empty bfq_queue, and thus the switch from idle to busy of the
bfq_queue, may cause the scenario to change, and make plugging no
longer needed for service guarantees, or more convenient for
throughput. In this case, keeping I/O-dispatch plugged would certainly
lower throughput.
To address this issue, this commit makes such a check, and stops
plugging I/O if it is better to stop plugging I/O.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Some BFQ mechanisms make their decisions on a bfq_queue basing also on
whether the bfq_queue is I/O bound. In this respect, the current logic
for evaluating whether a bfq_queue is I/O bound is rather rough. This
commits replaces this logic with a more effective one.
The new logic measures the percentage of time during which a bfq_queue
is active, and marks the bfq_queue as I/O bound if the latter if this
percentage is above a fixed threshold.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This reverts commit b445547ec1.
Since both mq-deadline and BFQ completely ignore hctx they are passed to
their dispatch function and dispatch whatever request they deem fit
checking whether any request for a particular hctx is queued is just
pointless since we'll very likely get a request from a different hctx
anyway. In the following commit we'll deal with lock contention in these
IO schedulers in presence of multiple HW queues in a different way.
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commits preserves I/O-dispatch plugging for a special symmetric
case that may suddenly turn into asymmetric: the case where only one
bfq_queue, say bfqq, is busy. In this case, not expiring bfqq does not
cause any harm to any other queues in terms of service guarantees. In
contrast, it avoids the following unlucky sequence of events: (1) bfqq
is expired, (2) a new queue with a lower weight than bfqq becomes busy
(or more queues), (3) the new queue is served until a new request
arrives for bfqq, (4) when bfqq is finally served, there are so many
requests of the new queue in the drive that the pending requests for
bfqq take a lot of time to be served. In particular, event (2) may
case even already dispatched requests of bfqq to be delayed, inside
the drive. So, to avoid this series of events, the scenario is
preventively declared as asymmetric also if bfqq is the only busy
queues. By doing so, I/O-dispatch plugging is performed for bfqq.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
BFQ tags some bfq_queues as interactive or soft_rt if it deems that
these bfq_queues contain the I/O of, respectively, interactive or soft
real-time applications. BFQ privileges both these special types of
bfq_queues over normal bfq_queues. To privilege a bfq_queue, BFQ
mainly raises the weight of the bfq_queue. In particular, soft_rt
bfq_queues get a higher weight than interactive bfq_queues.
A bfq_queue may turn from interactive to soft_rt. And this leads to a
tricky issue. Soft real-time applications usually start with an
I/O-bound, interactive phase, in which they load themselves into main
memory. BFQ correctly detects this phase, and keeps the bfq_queues
associated with the application in interactive mode for a
while. Problems arise when the I/O pattern of the application finally
switches to soft real-time. One of the conditions for a bfq_queue to
be deemed as soft_rt is that the bfq_queue does not consume too much
bandwidth. But the bfq_queues associated with a soft real-time
application consume as much bandwidth as they can in the loading phase
of the application. So, after the application becomes truly soft
real-time, a lot of time should pass before the average bandwidth
consumed by its bfq_queues finally drops to a value acceptable for
soft_rt bfq_queues. As a consequence, there might be a time gap during
which the application is not privileged at all, because its bfq_queues
are not interactive any longer, but cannot be deemed as soft_rt yet.
To avoid this problem, BFQ pretends that an interactive bfq_queue
consumes zero bandwidth, and allows an interactive bfq_queue to switch
to soft_rt. Yet, this fake zero-bandwidth consumption easily causes
the bfq_queue to often switch to soft_rt deceptively, during its
loading phase. As in soft_rt mode, the bfq_queue gets its bandwidth
correctly computed, and therefore soon switches back to
interactive. Then it switches again to soft_rt, and so on. These
spurious fluctuations usually cause losses of throughput, because they
deceive BFQ's mechanisms for boosting throughput (injection,
I/O-plugging avoidance, ...).
This commit addresses this issue as follows:
1) It does compute actual bandwidth consumption also for interactive
bfq_queues. This avoids the above false positives.
2) When a bfq_queue switches from interactive to normal mode, the
consumed bandwidth is reset (forgotten). This allows the
bfq_queue to enjoy soft_rt very quickly. In particular, two
alternatives are possible in this switch:
- the bfq_queue still has backlog, and therefore there is a budget
already scheduled to serve the bfq_queue; in this case, the
scheduling of the current budget of the bfq_queue is not
hindered, because only the scheduling of the next budget will
be affected by the weight drop. After that, if the bfq_queue is
actually in a soft_rt phase, and becomes empty during the
service of its current budget, which is the natural behavior of
a soft_rt bfq_queue, then the bfq_queue will be considered as
soft_rt when its next I/O arrives. If, in contrast, the
bfq_queue remains constantly non-empty, then its next budget
will be scheduled with a low weight, which is the natural
treatment for an I/O-bound (non soft_rt) bfq_queue.
- the bfq_queue is empty; in this case, the bfq_queue may be
considered unjustly soft_rt when its new I/O arrives. Yet
the problem is now much smaller than before, because it is
unlikely that more than one spurious fluctuation occurs.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
BFQ heuristics try to detect interactive I/O, and raise the weight of
the queues containing such an I/O. Yet, if also the user changes the
weight of a queue (i.e., the user changes the ioprio of the process
associated with that queue), then it is most likely better to prevent
BFQ heuristics from silently changing the same weight.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Tests on slower machines showed current window to be way too
small. This commit increases it.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Since commit c5089591c3ba ("block, bfq: detect wakers and
unconditionally inject their I/O"), when the in-service bfq_queue, say
Q, is temporarily empty, BFQ checks whether there are I/O requests to
inject (also) from the waker bfq_queue for Q. To this goal, the value
pointed by bfqq->waker_bfqq->next_rq must be controlled. However, the
current implementation mistakenly looks at bfqq->next_rq, which
instead points to the next request of the currently served queue.
This mistake evidently causes losses of throughput in scenarios with
waker bfq_queues.
This commit corrects this mistake.
Fixes: c5089591c3ba ("block, bfq: detect wakers and unconditionally inject their I/O")
Signed-off-by: Jia Cheng Hu <jia.jiachenghu@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The value of the I/O plugging (idling) timeout is used also as the
think-time threshold to decide whether a process has a short think
time. In this respect, a good value of this timeout for rotational
drives is un the order of several ms. Yet, this is often too long a
time interval to be effective as a think-time threshold. This commit
mitigates this problem (by a lot, according to tests), by halving the
threshold.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
BFQ computes number of tags it allows to be allocated for each request type
based on tag bitmap. However it uses 1 << bitmap.shift as number of
available tags which is wrong. 'shift' is just an internal bitmap value
containing logarithm of how many bits bitmap uses in each bitmap word.
Thus number of tags allowed for some request types can be far to low.
Use proper bitmap.depth which has the number of tags instead.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Merge tag 'block-5.10-2020-10-12' of git://git.kernel.dk/linux-block
Pull block updates from Jens Axboe:
- Series of merge handling cleanups (Baolin, Christoph)
- Series of blk-throttle fixes and cleanups (Baolin)
- Series cleaning up BDI, seperating the block device from the
backing_dev_info (Christoph)
- Removal of bdget() as a generic API (Christoph)
- Removal of blkdev_get() as a generic API (Christoph)
- Cleanup of is-partition checks (Christoph)
- Series reworking disk revalidation (Christoph)
- Series cleaning up bio flags (Christoph)
- bio crypt fixes (Eric)
- IO stats inflight tweak (Gabriel)
- blk-mq tags fixes (Hannes)
- Buffer invalidation fixes (Jan)
- Allow soft limits for zone append (Johannes)
- Shared tag set improvements (John, Kashyap)
- Allow IOPRIO_CLASS_RT for CAP_SYS_NICE (Khazhismel)
- DM no-wait support (Mike, Konstantin)
- Request allocation improvements (Ming)
- Allow md/dm/bcache to use IO stat helpers (Song)
- Series improving blk-iocost (Tejun)
- Various cleanups (Geert, Damien, Danny, Julia, Tetsuo, Tian, Wang,
Xianting, Yang, Yufen, yangerkun)
* tag 'block-5.10-2020-10-12' of git://git.kernel.dk/linux-block: (191 commits)
block: fix uapi blkzoned.h comments
blk-mq: move cancel of hctx->run_work to the front of blk_exit_queue
blk-mq: get rid of the dead flush handle code path
block: get rid of unnecessary local variable
block: fix comment and add lockdep assert
blk-mq: use helper function to test hw stopped
block: use helper function to test queue register
block: remove redundant mq check
block: invoke blk_mq_exit_sched no matter whether have .exit_sched
percpu_ref: don't refer to ref->data if it isn't allocated
block: ratelimit handle_bad_sector() message
blk-throttle: Re-use the throtl_set_slice_end()
blk-throttle: Open code __throtl_de/enqueue_tg()
blk-throttle: Move service tree validation out of the throtl_rb_first()
blk-throttle: Move the list operation after list validation
blk-throttle: Fix IO hang for a corner case
blk-throttle: Avoid tracking latency if low limit is invalid
blk-throttle: Avoid getting the current time if tg->last_finish_time is 0
blk-throttle: Remove a meaningless parameter for throtl_downgrade_state()
block: Remove redundant 'return' statement
...
- NVMe pull request from Christoph:
- cancel async events before freeing them (David Milburn)
- revert a broken race fix (James Smart)
- fix command processing during resets (Sagi Grimberg)
- Fix a kyber crash with requeued flushes (Omar)
- Fix __bio_try_merge_page() same_page error for no merging (Ritesh)
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Merge tag 'block-5.9-2020-09-11' of git://git.kernel.dk/linux-block
Pull block fixes from Jens Axboe:
- Fix a regression in bdev partition locking (Christoph)
- NVMe pull request from Christoph:
- cancel async events before freeing them (David Milburn)
- revert a broken race fix (James Smart)
- fix command processing during resets (Sagi Grimberg)
- Fix a kyber crash with requeued flushes (Omar)
- Fix __bio_try_merge_page() same_page error for no merging (Ritesh)
* tag 'block-5.9-2020-09-11' of git://git.kernel.dk/linux-block:
block: Set same_page to false in __bio_try_merge_page if ret is false
nvme-fabrics: allow to queue requests for live queues
block: only call sched requeue_request() for scheduled requests
nvme-tcp: cancel async events before freeing event struct
nvme-rdma: cancel async events before freeing event struct
nvme-fc: cancel async events before freeing event struct
nvme: Revert: Fix controller creation races with teardown flow
block: restore a specific error code in bdev_del_partition
Yang Yang reported the following crash caused by requeueing a flush
request in Kyber:
[ 2.517297] Unable to handle kernel paging request at virtual address ffffffd8071c0b00
...
[ 2.517468] pc : clear_bit+0x18/0x2c
[ 2.517502] lr : sbitmap_queue_clear+0x40/0x228
[ 2.517503] sp : ffffff800832bc60 pstate : 00c00145
...
[ 2.517599] Process ksoftirqd/5 (pid: 51, stack limit = 0xffffff8008328000)
[ 2.517602] Call trace:
[ 2.517606] clear_bit+0x18/0x2c
[ 2.517619] kyber_finish_request+0x74/0x80
[ 2.517627] blk_mq_requeue_request+0x3c/0xc0
[ 2.517637] __scsi_queue_insert+0x11c/0x148
[ 2.517640] scsi_softirq_done+0x114/0x130
[ 2.517643] blk_done_softirq+0x7c/0xb0
[ 2.517651] __do_softirq+0x208/0x3bc
[ 2.517657] run_ksoftirqd+0x34/0x60
[ 2.517663] smpboot_thread_fn+0x1c4/0x2c0
[ 2.517667] kthread+0x110/0x120
[ 2.517669] ret_from_fork+0x10/0x18
This happens because Kyber doesn't track flush requests, so
kyber_finish_request() reads a garbage domain token. Only call the
scheduler's requeue_request() hook if RQF_ELVPRIV is set (like we do for
the finish_request() hook in blk_mq_free_request()). Now that we're
handling it in blk-mq, also remove the check from BFQ.
Reported-by: Yang Yang <yang.yang@vivo.com>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Paolo Valente
Christoph Hellwig
Damien Le Moal
Ming Lei
Jan Kara
Pietro Pedroni
Luca Mariotti
Omar Sandoval
Lin Feng
Joseph Qi
Chaitanya Kulkarni
Linus Torvalds
Jens Axboe
Jia Cheng Hu