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2019-08-15dm kcopyd: always complete failed jobsDmitry Fomichev1-1/+4
This patch fixes a problem in dm-kcopyd that may leave jobs in complete queue indefinitely in the event of backing storage failure. This behavior has been observed while running 100% write file fio workload against an XFS volume created on top of a dm-zoned target device. If the underlying storage of dm-zoned goes to offline state under I/O, kcopyd sometimes never issues the end copy callback and dm-zoned reclaim work hangs indefinitely waiting for that completion. This behavior was traced down to the error handling code in process_jobs() function that places the failed job to complete_jobs queue, but doesn't wake up the job handler. In case of backing device failure, all outstanding jobs may end up going to complete_jobs queue via this code path and then stay there forever because there are no more successful I/O jobs to wake up the job handler. This patch adds a wake() call to always wake up kcopyd job wait queue for all I/O jobs that fail before dm_io() gets called for that job. The patch also sets the write error status in all sub jobs that are failed because their master job has failed. Fixes: b73c67c2cbb00 ("dm kcopyd: add sequential write feature") Cc: stable@vger.kernel.org Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com> Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2019-07-17dm kcopyd: Increase default sub-job size to 512KBNikos Tsironis1-6/+28
Currently, kcopyd has a sub-job size of 64KB and a maximum number of 8 sub-jobs. As a result, for any kcopyd job, we have a maximum of 512KB of I/O in flight. This upper limit to the amount of in-flight I/O under-utilizes fast devices and results in decreased throughput, e.g., when writing to a snapshotted thin LV with I/O size less than the pool's block size (so COW is performed using kcopyd). Increase kcopyd's default sub-job size to 512KB, so we have a maximum of 4MB of I/O in flight for each kcopyd job. This results in an up to 96% improvement of bandwidth when writing to a snapshotted thin LV, with I/O sizes less than the pool's block size. Also, add dm_mod.kcopyd_subjob_size_kb module parameter to allow users to fine tune the sub-job size of kcopyd. The default value of this parameter is 512KB and the maximum allowed value is 1024KB. We evaluate the performance impact of the change by running the snap_breaking_throughput benchmark, from the device mapper test suite [1]. The benchmark: 1. Creates a 1G thin LV 2. Provisions the thin LV 3. Takes a snapshot of the thin LV 4. Writes to the thin LV with: dd if=/dev/zero of=/dev/vg/thin_lv oflag=direct bs=<I/O size> Running this benchmark with various thin pool block sizes and dd I/O sizes (all combinations triggering the use of kcopyd) we get the following results: +-----------------+-------------+------------------+-----------------+ | Pool block size | dd I/O size | BW before (MB/s) | BW after (MB/s) | +-----------------+-------------+------------------+-----------------+ | 1 MB | 256 KB | 242 | 280 | | 1 MB | 512 KB | 238 | 295 | | | | | | | 2 MB | 256 KB | 238 | 354 | | 2 MB | 512 KB | 241 | 380 | | 2 MB | 1 MB | 245 | 394 | | | | | | | 4 MB | 256 KB | 248 | 412 | | 4 MB | 512 KB | 234 | 432 | | 4 MB | 1 MB | 251 | 474 | | 4 MB | 2 MB | 257 | 504 | | | | | | | 8 MB | 256 KB | 239 | 420 | | 8 MB | 512 KB | 256 | 431 | | 8 MB | 1 MB | 264 | 467 | | 8 MB | 2 MB | 264 | 502 | | 8 MB | 4 MB | 281 | 537 | +-----------------+-------------+------------------+-----------------+ [1] https://github.com/jthornber/device-mapper-test-suite Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2018-12-18dm kcopyd: Fix bug causing workqueue stallsNikos Tsironis1-5/+14
When using kcopyd to run callbacks through dm_kcopyd_do_callback() or submitting copy jobs with a source size of 0, the jobs are pushed directly to the complete_jobs list, which could be under processing by the kcopyd thread. As a result, the kcopyd thread can continue running completed jobs indefinitely, without releasing the CPU, as long as someone keeps submitting new completed jobs through the aforementioned paths. Processing of work items, queued for execution on the same CPU as the currently running kcopyd thread, is thus stalled for excessive amounts of time, hurting performance. Running the following test, from the device mapper test suite [1], dmtest run --suite snapshot -n parallel_io_to_many_snaps_N , with 8 active snapshots, we get, in dmesg, messages like the following: [68899.948523] BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 95s! [68899.949282] Showing busy workqueues and worker pools: [68899.949288] workqueue events: flags=0x0 [68899.949295] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 [68899.949306] pending: vmstat_shepherd, cache_reap [68899.949331] workqueue mm_percpu_wq: flags=0x8 [68899.949337] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 [68899.949345] pending: vmstat_update [68899.949387] workqueue dm_bufio_cache: flags=0x8 [68899.949392] pwq 4: cpus=2 node=0 flags=0x0 nice=0 active=1/256 [68899.949400] pending: work_fn [dm_bufio] [68899.949423] workqueue kcopyd: flags=0x8 [68899.949429] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 [68899.949437] pending: do_work [dm_mod] [68899.949452] workqueue kcopyd: flags=0x8 [68899.949458] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=2/256 [68899.949466] in-flight: 13:do_work [dm_mod] [68899.949474] pending: do_work [dm_mod] [68899.949487] workqueue kcopyd: flags=0x8 [68899.949493] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 [68899.949501] pending: do_work [dm_mod] [68899.949515] workqueue kcopyd: flags=0x8 [68899.949521] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 [68899.949529] pending: do_work [dm_mod] [68899.949541] workqueue kcopyd: flags=0x8 [68899.949547] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 [68899.949555] pending: do_work [dm_mod] [68899.949568] pool 0: cpus=0 node=0 flags=0x0 nice=0 hung=95s workers=4 idle: 27130 27223 1084 Fix this by splitting the complete_jobs list into two parts: A user facing part, named callback_jobs, and one used internally by kcopyd, retaining the name complete_jobs. dm_kcopyd_do_callback() and dispatch_job() now push their jobs to the callback_jobs list, which is spliced to the complete_jobs list once, every time the kcopyd thread wakes up. This prevents kcopyd from hogging the CPU indefinitely and causing workqueue stalls. Re-running the aforementioned test: * Workqueue stalls are eliminated * The maximum writing time among all targets is reduced from 09m37.10s to 06m04.85s and the total run time of the test is reduced from 10m43.591s to 7m19.199s [1] https://github.com/jthornber/device-mapper-test-suite Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com> Signed-off-by: Ilias Tsitsimpis <iliastsi@arrikto.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2018-08-08dm kcopyd: avoid softlockup in run_complete_jobJohn Pittman1-0/+2
It was reported that softlockups occur when using dm-snapshot ontop of slow (rbd) storage. E.g.: [ 4047.990647] watchdog: BUG: soft lockup - CPU#10 stuck for 22s! [kworker/10:23:26177] ... [ 4048.034151] Workqueue: kcopyd do_work [dm_mod] [ 4048.034156] RIP: 0010:copy_callback+0x41/0x160 [dm_snapshot] ... [ 4048.034190] Call Trace: [ 4048.034196] ? __chunk_is_tracked+0x70/0x70 [dm_snapshot] [ 4048.034200] run_complete_job+0x5f/0xb0 [dm_mod] [ 4048.034205] process_jobs+0x91/0x220 [dm_mod] [ 4048.034210] ? kcopyd_put_pages+0x40/0x40 [dm_mod] [ 4048.034214] do_work+0x46/0xa0 [dm_mod] [ 4048.034219] process_one_work+0x171/0x370 [ 4048.034221] worker_thread+0x1fc/0x3f0 [ 4048.034224] kthread+0xf8/0x130 [ 4048.034226] ? max_active_store+0x80/0x80 [ 4048.034227] ? kthread_bind+0x10/0x10 [ 4048.034231] ret_from_fork+0x35/0x40 [ 4048.034233] Kernel panic - not syncing: softlockup: hung tasks Fix this by calling cond_resched() after run_complete_job()'s callout to the dm_kcopyd_notify_fn (which is dm-snap.c:copy_callback in the above trace). Signed-off-by: John Pittman <jpittman@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2018-07-31dm kcopyd: return void from dm_kcopyd_copy()Mike Snitzer1-9/+7
dm_kcopyd_copy() only ever returns 0 so there is no need for callers to account for possible failure. Same goes for dm_kcopyd_zero(). Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2018-06-08dm: adjust structure members to improve alignmentMike Snitzer1-1/+2
Eliminate most holes in DM data structures that were modified by commit 6f1c819c21 ("dm: convert to bioset_init()/mempool_init()"). Also prevent structure members from unnecessarily spanning cache lines. Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2018-06-05dm: Use kzalloc for all structs with embedded biosets/mempoolsKent Overstreet1-1/+1
mempool_init()/bioset_init() require that the mempools/biosets be zeroed first; they probably should not _require_ this, but not allocating those structs with kzalloc is a fairly nonsensical thing to do (calling mempool_exit()/bioset_exit() on an uninitialized mempool/bioset is legal and safe, but only works if said memory was zeroed.) Acked-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-05-30dm: convert to bioset_init()/mempool_init()Kent Overstreet1-10/+12
Convert dm to embedded bio sets. Acked-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-01-17dm: backfill missing calls to mutex_destroy()Mike Snitzer1-2/+4
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2017-10-25locking/atomics: COCCINELLE/treewide: Convert trivial ACCESS_ONCE() patterns ↵Mark Rutland1-2/+2
to READ_ONCE()/WRITE_ONCE() Please do not apply this to mainline directly, instead please re-run the coccinelle script shown below and apply its output. For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't harmful, and changing them results in churn. However, for some features, the read/write distinction is critical to correct operation. To distinguish these cases, separate read/write accessors must be used. This patch migrates (most) remaining ACCESS_ONCE() instances to {READ,WRITE}_ONCE(), using the following coccinelle script: ---- // Convert trivial ACCESS_ONCE() uses to equivalent READ_ONCE() and // WRITE_ONCE() // $ make coccicheck COCCI=/home/mark/once.cocci SPFLAGS="--include-headers" MODE=patch virtual patch @ depends on patch @ expression E1, E2; @@ - ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2) @ depends on patch @ expression E; @@ - ACCESS_ONCE(E) + READ_ONCE(E) ---- Signed-off-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: davem@davemloft.net Cc: linux-arch@vger.kernel.org Cc: mpe@ellerman.id.au Cc: shuah@kernel.org Cc: snitzer@redhat.com Cc: thor.thayer@linux.intel.com Cc: tj@kernel.org Cc: viro@zeniv.linux.org.uk Cc: will.deacon@arm.com Link: http://lkml.kernel.org/r/1508792849-3115-19-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-06-19dm kcopyd: add sequential write featureDamien Le Moal1-2/+63
When copyying blocks to host-managed zoned block devices, writes must be sequential. However, dm_kcopyd_copy() does not guarantee this as writes are issued in the completion order of reads, and reads may complete out of order despite being issued sequentially. Fix this by introducing the DM_KCOPYD_WRITE_SEQ feature flag. This can be specified when calling dm_kcopyd_copy() and should be set automatically if one of the destinations is a host-managed zoned block device. For a split job, the master job maintains the write position at which writes must be issued. This is checked with the pop() function which is modified to not return any write I/O sub job that is not at the correct write position. When DM_KCOPYD_WRITE_SEQ is specified for a job, errors cannot be ignored and the flag DM_KCOPYD_IGNORE_ERROR is ignored, even if specified by the user. Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com> Reviewed-by: Hannes Reinecke <hare@suse.com> Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
2017-04-08dm kcopyd: switch to use REQ_OP_WRITE_ZEROESChristoph Hellwig1-3/+3
It seems like the code currently passes whatever it was using for writes to WRITE SAME. Just switch it to WRITE ZEROES, although that doesn't need any payload. Untested, and confused by the code, maybe someone who understands it better than me can help.. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Hannes Reinecke <hare@suse.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-06-10dm: move request-based code out to dm-rq.[hc]Mike Snitzer1-1/+1
Add some seperation between bio-based and request-based DM core code. 'struct mapped_device' and other DM core only structures and functions have been moved to dm-core.h and all relevant DM core .c files have been updated to include dm-core.h rather than dm.h DM targets should _never_ include dm-core.h! [block core merge conflict resolution from Stephen Rothwell] Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
2016-06-07dm: use bio op accessorsMike Christie1-2/+3
Separate the op from the rq_flag_bits and have dm set/get the bio using bio_set_op_attrs/bio_op. Signed-off-by: Mike Christie <mchristi@redhat.com> Reviewed-by: Hannes Reinecke <hare@suse.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2016-06-07dm: use op_is_write instead of checking for REQ_WRITEMike Christie1-3/+3
We currently set REQ_WRITE/WRITE for all non READ IOs like discard, flush, writesame, etc. In the next patches where we no longer set up the op as a bitmap, we will not be able to detect a operation direction like writesame by testing if REQ_WRITE is set. This has dm use the op_is_write helper which will do the right thing. Signed-off-by: Mike Christie <mchristi@redhat.com> Reviewed-by: Hannes Reinecke <hare@suse.com> Signed-off-by: Jens Axboe <axboe@fb.com>
2015-11-06mm, page_alloc: distinguish between being unable to sleep, unwilling to ↵Mel Gorman1-1/+1
sleep and avoiding waking kswapd __GFP_WAIT has been used to identify atomic context in callers that hold spinlocks or are in interrupts. They are expected to be high priority and have access one of two watermarks lower than "min" which can be referred to as the "atomic reserve". __GFP_HIGH users get access to the first lower watermark and can be called the "high priority reserve". Over time, callers had a requirement to not block when fallback options were available. Some have abused __GFP_WAIT leading to a situation where an optimisitic allocation with a fallback option can access atomic reserves. This patch uses __GFP_ATOMIC to identify callers that are truely atomic, cannot sleep and have no alternative. High priority users continue to use __GFP_HIGH. __GFP_DIRECT_RECLAIM identifies callers that can sleep and are willing to enter direct reclaim. __GFP_KSWAPD_RECLAIM to identify callers that want to wake kswapd for background reclaim. __GFP_WAIT is redefined as a caller that is willing to enter direct reclaim and wake kswapd for background reclaim. This patch then converts a number of sites o __GFP_ATOMIC is used by callers that are high priority and have memory pools for those requests. GFP_ATOMIC uses this flag. o Callers that have a limited mempool to guarantee forward progress clear __GFP_DIRECT_RECLAIM but keep __GFP_KSWAPD_RECLAIM. bio allocations fall into this category where kswapd will still be woken but atomic reserves are not used as there is a one-entry mempool to guarantee progress. o Callers that are checking if they are non-blocking should use the helper gfpflags_allow_blocking() where possible. This is because checking for __GFP_WAIT as was done historically now can trigger false positives. Some exceptions like dm-crypt.c exist where the code intent is clearer if __GFP_DIRECT_RECLAIM is used instead of the helper due to flag manipulations. o Callers that built their own GFP flags instead of starting with GFP_KERNEL and friends now also need to specify __GFP_KSWAPD_RECLAIM. The first key hazard to watch out for is callers that removed __GFP_WAIT and was depending on access to atomic reserves for inconspicuous reasons. In some cases it may be appropriate for them to use __GFP_HIGH. The second key hazard is callers that assembled their own combination of GFP flags instead of starting with something like GFP_KERNEL. They may now wish to specify __GFP_KSWAPD_RECLAIM. It's almost certainly harmless if it's missed in most cases as other activity will wake kswapd. Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Acked-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Johannes Weiner <hannes@cmpxchg.org> Cc: Christoph Lameter <cl@linux.com> Cc: David Rientjes <rientjes@google.com> Cc: Vitaly Wool <vitalywool@gmail.com> Cc: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2013-08-23dm: stop using WQ_NON_REENTRANTTejun Heo1-2/+1
dbf2576e37 ("workqueue: make all workqueues non-reentrant") made WQ_NON_REENTRANT no-op and the flag is going away. Remove its usages. This patch doesn't introduce any behavior changes. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com> Acked-by: Joe Thornber <ejt@redhat.com>
2013-03-01dm kcopyd: introduce configurable throttlingMikulas Patocka1-1/+120
This patch allows the administrator to reduce the rate at which kcopyd issues I/O. Each module that uses kcopyd acquires a throttle parameter that can be set in /sys/module/*/parameters. We maintain a history of kcopyd usage by each module in the variables io_period and total_period in struct dm_kcopyd_throttle. The actual kcopyd activity is calculated as a percentage of time equal to "(100 * io_period / total_period)". This is compared with the user-defined throttle percentage threshold and if it is exceeded, we sleep. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2012-12-21dm kcopyd: add WRITE SAME support to dm_kcopyd_zeroMike Snitzer1-4/+14
Add WRITE SAME support to dm-io and make it accessible to dm_kcopyd_zero(). dm_kcopyd_zero() provides an asynchronous interface whereas the blkdev_issue_write_same() interface is synchronous. WRITE SAME is a SCSI command that can be leveraged for more efficient zeroing of a specified logical extent of a device which supports it. Only a single zeroed logical block is transfered to the target for each WRITE SAME and the target then writes that same block across the specified extent. The dm thin target uses this. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-10-31dm kcopyd: add dm_kcopyd_zero to zero an areaMikulas Patocka1-5/+26
This patch introduces dm_kcopyd_zero() to make it easy to use kcopyd to write zeros into the requested areas instead instead of copying. It is implemented by passing a NULL copying source to dm_kcopyd_copy(). The forthcoming thin provisioning target uses this. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-10-23dm kcopyd: fix job_pool leakAlasdair G Kergon1-0/+1
Fix memory leak introduced by commit a6e50b409d3f9e0833e69c3c9cca822e8fa4adbb (dm snapshot: skip reading origin when overwriting complete chunk). When allocating a set of jobs from kc->job_pool, job->master_job must be set (to point to itself) so that the mempool item gets freed when the master_job completes. master_job was introduced by commit c6ea41fbbe08f270a8edef99dc369faf809d1bd6 (dm kcopyd: preallocate sub jobs to avoid deadlock) Reported-by: Michael Leun <ml@newton.leun.net> Cc: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-08-02dm snapshot: skip reading origin when overwriting complete chunkMikulas Patocka1-0/+31
If we write a full chunk in the snapshot, skip reading the origin device because the whole chunk will be overwritten anyway. This patch changes the snapshot write logic when a full chunk is written. In this case: 1. allocate the exception 2. dispatch the bio (but don't report the bio completion to device mapper) 3. write the exception record 4. report bio completed Callbacks must be done through the kcopyd thread, because callbacks must not race with each other. So we create two new functions: dm_kcopyd_prepare_callback: allocate a job structure and prepare the callback. (This function must not be called from interrupt context.) dm_kcopyd_do_callback: submit callback. (This function may be called from interrupt context.) Performance test (on snapshots with 4k chunk size): without the patch: non-direct-io sequential write (dd): 17.7MB/s direct-io sequential write (dd): 20.9MB/s non-direct-io random write (mkfs.ext2): 0.44s with the patch: non-direct-io sequential write (dd): 26.5MB/s direct-io sequential write (dd): 33.2MB/s non-direct-io random write (mkfs.ext2): 0.27s Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-08-02dm kcopyd: remove nr_pages field from job structureMikulas Patocka1-4/+2
The nr_pages field in struct kcopyd_job is only used temporarily in run_pages_job() to count the number of required pages. We can use a local variable instead. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-08-02dm kcopyd: remove offset field from job structureMikulas Patocka1-5/+2
The offset field in struct kcopyd_job is always zero so remove it. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-07-26atomic: use <linux/atomic.h>Arun Sharma1-1/+1
This allows us to move duplicated code in <asm/atomic.h> (atomic_inc_not_zero() for now) to <linux/atomic.h> Signed-off-by: Arun Sharma <asharma@fb.com> Reviewed-by: Eric Dumazet <eric.dumazet@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: David Miller <davem@davemloft.net> Cc: Eric Dumazet <eric.dumazet@gmail.com> Acked-by: Mike Frysinger <vapier@gentoo.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-05-29dm kcopyd: return client directly and not through a pointerMikulas Patocka1-5/+4
Return client directly from dm_kcopyd_client_create, not through a parameter, making it consistent with dm_io_client_create. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-05-29dm kcopyd: reserve fewer pagesMikulas Patocka1-3/+3
Reserve just the minimum of pages needed to process one job. Because we allocate pages from page allocator, we don't need to reserve a large number of pages. The maximum job size is SUB_JOB_SIZE and we calculate the number of reserved pages based on this. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-05-29dm io: use fixed initial mempool sizeMikulas Patocka1-1/+1
Replace the arbitrary calculation of an initial io struct mempool size with a constant. The code calculated the number of reserved structures based on the request size and used a "magic" multiplication constant of 4. This patch changes it to reserve a fixed number - itself still chosen quite arbitrarily. Further testing might show if there is a better number to choose. Note that if there is no memory pressure, we can still allocate an arbitrary number of "struct io" structures. One structure is enough to process the whole request. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-05-29dm kcopyd: alloc pages from the main page allocatorMikulas Patocka1-31/+60
This patch changes dm-kcopyd so that it allocates pages from the main page allocator with __GFP_NOWARN | __GFP_NORETRY flags (so that it can fail in case of memory pressure). If the allocation fails, dm-kcopyd allocates pages from its own reserve. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-05-29dm kcopyd: add gfp parm to alloc_plMikulas Patocka1-4/+4
Introduce a parameter for gfp flags to alloc_pl() for use in following patches. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-05-29dm kcopyd: remove superfluous page allocation spinlockMikulas Patocka1-10/+1
Remove the spinlock protecting the pages allocation. The spinlock is only taken on initialization or from single-threaded workqueue. Therefore, the spinlock is useless. The spinlock is taken in kcopyd_get_pages and kcopyd_put_pages. kcopyd_get_pages is only called from run_pages_job, which is only called from process_jobs called from do_work. kcopyd_put_pages is called from client_alloc_pages (which is initialization function) or from run_complete_job. run_complete_job is only called from process_jobs called from do_work. Another spinlock, kc->job_lock is taken each time someone pushes or pops some work for the worker thread. Once we take kc->job_lock, we guarantee that any written memory is visible to the other CPUs. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-05-29dm kcopyd: preallocate sub jobs to avoid deadlockMikulas Patocka1-20/+29
There's a possible theoretical deadlock in dm-kcopyd because multiple allocations from the same mempool are required to finish a request. Avoid this by preallocating sub jobs. There is a mempool of 512 entries. Each request requires up to 9 entries from the mempool. If we have at least 57 concurrent requests running, the mempool may overflow and mempool allocations may start blocking until another entry is freed to the mempool. Because the same thread is used to free entries to the mempool and allocate entries from the mempool, this may result in a deadlock. This patch changes it so that one mempool entry contains all 9 "struct kcopyd_job" required to fulfill the whole request. The allocation is done only once in dm_kcopyd_copy and no further mempool allocations are done during request processing. If dm_kcopyd_copy is not run in the completion thread, this implementation is deadlock-free. MIN_JOBS needs reducing accordingly and we've chosen to reduce it further to 8. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-05-29dm kcopyd: avoid pointless job splittingMikulas Patocka1-1/+1
Don't split SUB_JOB_SIZE jobs If the job size equals SUB_JOB_SIZE, there is no point in splitting it. Splitting it just unnecessarily wastes time, because the split job size is SUB_JOB_SIZE too. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-03-10block: kill off REQ_UNPLUGJens Axboe1-4/+1
With the plugging now being explicitly controlled by the submitter, callers need not pass down unplugging hints to the block layer. If they want to unplug, it's because they manually plugged on their own - in which case, they should just unplug at will. Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2011-03-10block: remove per-queue pluggingJens Axboe1-47/+5
Code has been converted over to the new explicit on-stack plugging, and delay users have been converted to use the new API for that. So lets kill off the old plugging along with aops->sync_page(). Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2011-01-13dm: use non reentrant workqueues if equivalentTejun Heo1-1/+2
kmirrord_wq, kcopyd_work and md->wq are created per dm instance and serve only a single work item from the dm instance, so non-reentrant workqueues would provide the same ordering guarantees as ordered ones while allowing CPU affinity and use of the workqueues for other purposes. Switch them to non-reentrant workqueues. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-01-13dm: convert workqueues to alloc_orderedTejun Heo1-1/+1
Convert all create[_singlethread]_work() users to the new alloc[_ordered]_workqueue(). This conversion is mechanical and doesn't introduce any behavior change. Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-01-13dm kcopyd: delay unpluggingMikulas Patocka1-3/+51
Make kcopyd merge more I/O requests by using device unplugging. Without this patch, each I/O request is dispatched separately to the device. If the device supports tagged queuing, there are many small requests sent to the device. To improve performance, this patch will batch as many requests as possible, allowing the queue to merge consecutive requests, and send them to the device at once. In my tests (15k SCSI disk), this patch improves sequential write throughput: Sequential write throughput (chunksize of 4k, 32k, 512k) unpatched: 15.2, 18.5, 17.5 MB/s patched: 14.4, 22.6, 23.0 MB/s In most common uses (snapshot or two-way mirror), kcopyd is only used for two devices, one for reading and the other for writing, thus this optimization is implemented only for two devices. The optimization may be extended to n-way mirrors with some code complexity increase. We keep track of two block devices to unplug (one for read and the other for write) and unplug them when exiting "do_work" thread. If there are more devices used (in theory it could happen, in practice it is rare), we unplug immediately. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2011-01-13dm io: remove BIO_RW_SYNCIO flag from kcopydMikulas Patocka1-1/+1
Remove the REQ_SYNC flag to improve write throughput when writing to the origin with a snapshot on the same device (using the CFQ I/O scheduler). Sequential write throughput (chunksize of 4k, 32k, 512k) unpatched: 8.5, 8.6, 9.3 MB/s patched: 15.2, 18.5, 17.5 MB/s Snapshot exception reallocations are triggered by writes that are usually async, so mark the associated dm_io_request as async as well. This helps when using the CFQ I/O scheduler because it has separate queues for sync and async I/O. Async is optimized for throughput; sync for latency. With this change we're consciously favoring throughput over latency. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2010-08-07block: unify flags for struct bio and struct requestChristoph Hellwig1-1/+1
Remove the current bio flags and reuse the request flags for the bio, too. This allows to more easily trace the type of I/O from the filesystem down to the block driver. There were two flags in the bio that were missing in the requests: BIO_RW_UNPLUG and BIO_RW_AHEAD. Also I've renamed two request flags that had a superflous RW in them. Note that the flags are in bio.h despite having the REQ_ name - as blkdev.h includes bio.h that is the only way to go for now. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
2009-12-10dm kcopyd: accept zero size jobsMikulas Patocka1-1/+4
dm-kcopyd: accept zero-size jobs This patch changes dm-kcopyd so that it accepts zero-size jobs and completes them immediatelly via its completion thread. It is needed for multisnapshots snapshot resizing. When we are writing to a chunk beyond origin end, no copying is done. To simplify the code, we submit an empty request to kcopyd and let kcopyd complete it. If we didn't submit a request to kcopyd and called the completion routine immediatelly, it would violate the principle that completion is called only from one thread and it would need additional locking. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2009-04-09dm kcopyd: fix callback raceMikulas Patocka1-6/+11
If the thread calling dm_kcopyd_copy is delayed due to scheduling inside split_job/segment_complete and the subjobs complete before the loop in split_job completes, the kcopyd callback could be invoked from the thread that called dm_kcopyd_copy instead of the kcopyd workqueue. dm_kcopyd_copy -> split_job -> segment_complete -> job->fn() Snapshots depend on the fact that callbacks are called from the singlethreaded kcopyd workqueue and expect that there is no racing between individual callbacks. The racing between callbacks can lead to corruption of exception store and it can also mean that exception store callbacks are called twice for the same exception - a likely reason for crashes reported inside pending_complete() / remove_exception(). This patch fixes two problems: 1. job->fn being called from the thread that submitted the job (see above). - Fix: hand over the completion callback to the kcopyd thread. 2. job->fn(read_err, write_err, job->context); in segment_complete reports the error of the last subjob, not the union of all errors. - Fix: pass job->write_err to the callback to report all error bits (it is done already in run_complete_job) Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2009-04-09dm kcopyd: prepare for callback race fixMikulas Patocka1-2/+4
Use a variable in segment_complete() to point to the dm_kcopyd_client struct and only release job->pages in run_complete_job() if any are defined. These changes are needed by the next patch. Cc: stable@kernel.org Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2009-02-18block: fix bad definition of BIO_RW_SYNCJens Axboe1-1/+1
We can't OR shift values, so get rid of BIO_RW_SYNC and use BIO_RW_SYNCIO and BIO_RW_UNPLUG explicitly. This brings back the behaviour from before 213d9417fec62ef4c3675621b9364a667954d4dd. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-21dm: remove dm header from targetsMikulas Patocka1-0/+1
Change #include "dm.h" to #include <linux/device-mapper.h> in all targets. Targets should not need direct access to internal DM structures. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2008-10-21dm kcopyd: avoid queue shuffleKazuo Ito1-1/+12
Write throughput to LVM snapshot origin volume is an order of magnitude slower than those to LV without snapshots or snapshot target volumes, especially in the case of sequential writes with O_SYNC on. The following patch originally written by Kevin Jamieson and Jan Blunck and slightly modified for the current RCs by myself tries to improve the performance by modifying the behaviour of kcopyd, so that it pushes back an I/O job to the head of the job queue instead of the tail as process_jobs() currently does when it has to wait for free pages. This way, write requests aren't shuffled to cause extra seeks. I tested the patch against 2.6.27-rc5 and got the following results. The test is a dd command writing to snapshot origin followed by fsync to the file just created/updated. A couple of filesystem benchmarks gave me similar results in case of sequential writes, while random writes didn't suffer much. dd if=/dev/zero of=<somewhere on snapshot origin> bs=4096 count=... [conv=notrunc when updating] 1) linux 2.6.27-rc5 without the patch, write to snapshot origin, average throughput (MB/s) 10M 100M 1000M create,dd 511.46 610.72 11.81 create,dd+fsync 7.10 6.77 8.13 update,dd 431.63 917.41 12.75 update,dd+fsync 7.79 7.43 8.12 compared with write throughput to LV without any snapshots, all dd+fsync and 1000 MiB writes perform very poorly. 10M 100M 1000M create,dd 555.03 608.98 123.29 create,dd+fsync 114.27 72.78 76.65 update,dd 152.34 1267.27 124.04 update,dd+fsync 130.56 77.81 77.84 2) linux 2.6.27-rc5 with the patch, write to snapshot origin, average throughput (MB/s) 10M 100M 1000M create,dd 537.06 589.44 46.21 create,dd+fsync 31.63 29.19 29.23 update,dd 487.59 897.65 37.76 update,dd+fsync 34.12 30.07 26.85 Although still not on par with plain LV performance - cannot be avoided because it's copy on write anyway - this simple patch successfully improves throughtput of dd+fsync while not affecting the rest. Signed-off-by: Jan Blunck <jblunck@suse.de> Signed-off-by: Kazuo Ito <ito.kazuo@oss.ntt.co.jp> Signed-off-by: Alasdair G Kergon <agk@redhat.com> Cc: stable@kernel.org
2008-04-25dm: unplug queues in threadsMikulas Patocka1-1/+1
Remove an avoidable 3ms delay on some dm-raid1 and kcopyd I/O. It is specified that any submitted bio without BIO_RW_SYNC flag may plug the queue (i.e. block the requests from being dispatched to the physical device). The queue is unplugged when the caller calls blk_unplug() function. Usually, the sequence is that someone calls submit_bh to submit IO on a buffer. The IO plugs the queue and waits (to be possibly joined with other adjacent bios). Then, when the caller calls wait_on_buffer(), it unplugs the queue and submits the IOs to the disk. This was happenning: When doing O_SYNC writes, function fsync_buffers_list() submits a list of bios to dm_raid1, the bios are added to dm_raid1 write queue and kmirrord is woken up. fsync_buffers_list() calls wait_on_buffer(). That unplugs the queue, but there are no bios on the device queue as they are still in the dm_raid1 queue. wait_on_buffer() starts waiting until the IO is finished. kmirrord is scheduled, kmirrord takes bios and submits them to the devices. The submitted bio plugs the harddisk queue but there is no one to unplug it. (The process that called wait_on_buffer() is already sleeping.) So there is a 3ms timeout, after which the queues on the harddisks are unplugged and requests are processed. This 3ms timeout meant that in certain workloads (e.g. O_SYNC, 8kb writes), dm-raid1 is 10 times slower than md raid1. Every time we submit something asynchronously via dm_io, we must unplug the queue actually to send the request to the device. This patch adds an unplug call to kmirrord - while processing requests, it keeps the queue plugged (so that adjacent bios can be merged); when it finishes processing all the bios, it unplugs the queue to submit the bios. It also fixes kcopyd which has the same potential problem. All kcopyd requests are submitted with BIO_RW_SYNC. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com> Acked-by: Jens Axboe <jens.axboe@oracle.com>
2008-04-25dm: move include filesAlasdair G Kergon1-1/+1
Publish the dm-io, dm-log and dm-kcopyd headers in include/linux. Signed-off-by: Alasdair G Kergon <agk@redhat.com>
2008-04-25dm kcopyd: renameAlasdair G Kergon1-0/+654
Rename kcopyd.[ch] to dm-kcopyd.[ch]. Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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