Changelog
v2: Addressed Tyler Hicks comments
- added mutex_destroy()
- comment in lo_open()
- added lock around lo_disk in
===
In our environment we are using systemd portable containers in
squashfs formats, convert them into loop device, and mount.
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop5 7:5 0 76.4M 0 loop
`-BaseImageM1908 252:3 0 76.4M 1 crypt /BaseImageM1908
loop6 7:6 0 20K 0 loop
`-test_launchperf20 252:17 0 1.3M 1 crypt /app/test_launchperf20
loop7 7:7 0 20K 0 loop
`-test_launchperf18 252:4 0 1.5M 1 crypt /app/test_launchperf18
loop8 7:8 0 8K 0 loop
`-test_launchperf8 252:25 0 28K 1 crypt app/test_launchperf8
loop9 7:9 0 376K 0 loop
`-test_launchperf14 252:29 0 45.7M 1 crypt /app/test_launchperf14
loop10 7:10 0 16K 0 loop
`-test_launchperf4 252:11 0 968K 1 crypt app/test_launchperf4
loop11 7:11 0 1.2M 0 loop
`-test_launchperf17 252:26 0 150.4M 1 crypt /app/test_launchperf17
loop12 7:12 0 36K 0 loop
`-test_launchperf19 252:13 0 3.3M 1 crypt /app/test_launchperf19
loop13 7:13 0 8K 0 loop
...
We have over 50 loop devices which are mounted during boot.
We observed contentions around loop_ctl_mutex.
The sample contentions stacks:
Contention 1:
__blkdev_get()
bdev->bd_disk->fops->open()
lo_open()
mutex_lock_killable(&loop_ctl_mutex); <- contention
Contention 2:
__blkdev_put()
disk->fops->release()
lo_release()
mutex_lock(&loop_ctl_mutex); <- contention
With total time waiting for loop_ctl_mutex ~18.8s during boot (across 8
CPUs) on our machine (69 loop devices): 2.35s per CPU.
Scaling this lock eliminates this contention entirely, and improves the boot
performance by 2s on our machine.
Pavel Tatashin (1):
loop: scale loop device by introducing per device lock
drivers/block/loop.c | 99 ++++++++++++++++++++++++++------------------
drivers/block/loop.h | 1 +
2 files changed, 59 insertions(+), 41 deletions(-)
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2.25.1
