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  1. 21 Jul, 2016 6 commits
    • Toshi Kani's avatar
      dm: add infrastructure for DAX support · 545ed20e
      Toshi Kani authored 
      Change mapped device to implement direct_access function,
dm_blk_direct_access(), which calls a target direct_access function.
'struct target_type' is extended to have target direct_access interface.
This function limits direct accessible size to the dm_target's limit
with max_io_len().

Add dm_table_supports_dax() to iterate all targets and associated block
devices to check for DAX support.  To add DAX support to a DM target the
target must only implement the direct_access function.

Add a new dm type, DM_TYPE_DAX_BIO_BASED, which indicates that mapped
device supports DAX and is bio based.  This new type is used to assure
that all target devices have DAX support and remain that way after
QUEUE_FLAG_DAX is set in mapped device.

At initial table load, QUEUE_FLAG_DAX is set to mapped device when setting
DM_TYPE_DAX_BIO_BASED to the type.  Any subsequent table load to the
mapped device must have the same type, or else it fails per the check in
table_load().
Signed-off-by: default avatarToshi Kani <toshi.kani@hpe.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
      545ed20e
    • Mike Snitzer's avatar
      Merge remote-tracking branch 'jens/for-4.8/core' into dm-4.8 · e9ccb945
      Mike Snitzer authored 
      DM's DAX support depends on block core's newly added QUEUE_FLAG_DAX.
      e9ccb945
    • Tahsin Erdogan's avatar
      block: do not merge requests without consulting with io scheduler · 72ef799b
      Tahsin Erdogan authored 
      Before merging a bio into an existing request, io scheduler is called to
get its approval first. However, the requests that come from a plug
flush may get merged by block layer without consulting with io
scheduler.

In case of CFQ, this can cause fairness problems. For instance, if a
request gets merged into a low weight cgroup's request, high weight cgroup
now will depend on low weight cgroup to get scheduled. If high weigt cgroup
needs that io request to complete before submitting more requests, then it
will also lose its timeslice.

Following script demonstrates the problem. Group g1 has a low weight, g2
and g3 have equal high weights but g2's requests are adjacent to g1's
requests so they are subject to merging. Due to these merges, g2 gets
poor disk time allocation.

cat > cfq-merge-repro.sh << "EOF"
#!/bin/bash
set -e

IO_ROOT=/mnt-cgroup/io

mkdir -p $IO_ROOT

if ! mount | grep -qw $IO_ROOT; then
  mount -t cgroup none -oblkio $IO_ROOT
fi

cd $IO_ROOT

for i in g1 g2 g3; do
  if [ -d $i ]; then
    rmdir $i
  fi
done

mkdir g1 && echo 10 > g1/blkio.weight
mkdir g2 && echo 495 > g2/blkio.weight
mkdir g3 && echo 495 > g3/blkio.weight

RUNTIME=10

(echo $BASHPID > g1/cgroup.procs &&
 fio --readonly --name name1 --filename /dev/sdb \
     --rw read --size 64k --bs 64k --time_based \
     --runtime=$RUNTIME --offset=0k &> /dev/null)&

(echo $BASHPID > g2/cgroup.procs &&
 fio --readonly --name name1 --filename /dev/sdb \
     --rw read --size 64k --bs 64k --time_based \
     --runtime=$RUNTIME --offset=64k &> /dev/null)&

(echo $BASHPID > g3/cgroup.procs &&
 fio --readonly --name name1 --filename /dev/sdb \
     --rw read --size 64k --bs 64k --time_based \
     --runtime=$RUNTIME --offset=256k &> /dev/null)&

sleep $((RUNTIME+1))

for i in g1 g2 g3; do
  echo ---- $i ----
  cat $i/blkio.time
done

EOF
# ./cfq-merge-repro.sh
---- g1 ----
8:16 162
---- g2 ----
8:16 165
---- g3 ----
8:16 686

After applying the patch:

# ./cfq-merge-repro.sh
---- g1 ----
8:16 90
---- g2 ----
8:16 445
---- g3 ----
8:16 471
Signed-off-by: default avatarTahsin Erdogan <tahsin@google.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
      72ef799b
    • Bart Van Assche's avatar
      block: Fix spelling in a source code comment · 68bdf1ac
      Bart Van Assche authored 
      Signed-off-by: default avatarBart Van Assche <bart.vanassche@sandisk.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
      68bdf1ac
    • Yigal Korman's avatar
      block: expose QUEUE_FLAG_DAX in sysfs · ea6ca600
      Yigal Korman authored 
      Provides the ability to identify DAX enabled devices in userspace.
Signed-off-by: default avatarYigal Korman <yigal@plexistor.com>
Signed-off-by: default avatarToshi Kani <toshi.kani@hpe.com>
Acked-by: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
      ea6ca600
    • Toshi Kani's avatar
      block: add QUEUE_FLAG_DAX for devices to advertise their DAX support · 163d4baa
      Toshi Kani authored 
      Currently, presence of direct_access() in block_device_operations
indicates support of DAX on its block device.  Because
block_device_operations is instantiated with 'const', this DAX
capablity may not be enabled conditinally.

In preparation for supporting DAX to device-mapper devices, add
QUEUE_FLAG_DAX to request_queue flags to advertise their DAX
support.  This will allow to set the DAX capability based on how
mapped device is composed.
Signed-off-by: default avatarToshi Kani <toshi.kani@hpe.com>
Acked-by: default avatarDan Williams <dan.j.williams@intel.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: <linux-s390@vger.kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
      163d4baa
  3. 20 Jul, 2016 2 commits
    • Joe Thornber's avatar
      dm thin: fix a race condition between discarding and provisioning a block · 2a0fbffb
      Joe Thornber authored 
      The discard passdown was being issued after the block was unmapped,
which meant the block could be reprovisioned whilst the passdown discard
was still in flight.

We can only identify unshared blocks (safe to do a passdown a discard
to) once they're unmapped and their ref count hits zero.  Block ref
counts are now used to guard against concurrent allocation of these
blocks that are being discarded.  So now we unmap the block, issue
passdown discards, and the immediately increment ref counts for regions
that have been discarded via passed down (this is safe because
allocation occurs within the same thread).  We then decrement ref counts
once the passdown discard IO is complete -- signaling these blocks may
now be allocated.

This fixes the potential for corruption that was reported here:
https://www.redhat.com/archives/dm-devel/2016-June/msg00311.htmlReported-by: default avatarDennis Yang <dennisyang@qnap.com>
Signed-off-by: default avatarJoe Thornber <ejt@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
      2a0fbffb
    • Joe Thornber's avatar
      dm btree: fix a bug in dm_btree_find_next_single() · e7e0f730
      Joe Thornber authored 
      dm_btree_find_next_single() can short-circuit the search for a block
with a return of -ENODATA if all entries are higher than the search key
passed to lower_bound().

This hasn't been a problem because of the way the btree has been used by
DM thinp.  But it must be fixed now in preparation for fixing the race
in DM thinp's handling of simultaneous block discard vs allocation.
Otherwise, once that fix is in place, some of the blocks in a discard
would not be unmapped as expected.
Signed-off-by: default avatarJoe Thornber <ejt@redhat.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
      e7e0f730
  5. 19 Jul, 2016 2 commits
  7. 18 Jul, 2016 29 commits
  9. 13 Jul, 2016 1 commit
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