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mimic: bluestore: 50-100% iops lost due to bluefs_preextend_wal_files = false #28574

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merged 1 commit into from Jul 1, 2019

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smithfarm commented Jun 15, 2019

This function is only used by RocksDB WAL writing so it must sync data.

This fixes #18338 and thus allows to actually set `bluefs_preextend_wal_files`
to true, gaining +100% single-thread write iops in disk-bound (HDD or bad SSD) setups.
To my knowledge it doesn't hurt performance in other cases.
Test it yourself on any HDD with `fio -ioengine=rbd -direct=1 -bs=4k -iodepth=1`.

Issue #18338 is easily reproduced without this patch by issuing a `kill -9` to the OSD
while doing `fio -ioengine=rbd -direct=1 -bs=4M -iodepth=16`.

Fixes: https://tracker.ceph.com/issues/18338 https://tracker.ceph.com/issues/38559
Signed-off-by: Vitaliy Filippov <vitalif@yourcmc.ru>
(cherry picked from commit c703cf9)

Conflicts:
	src/os/bluestore/KernelDevice.cc
- mimic has a single variable "fd_buffered" where master has an array "fd_buffereds"
@smithfarm smithfarm self-assigned this Jun 15, 2019
@smithfarm smithfarm added this to the mimic milestone Jun 15, 2019
@smithfarm smithfarm changed the title mimic: 50-100% iops lost due to bluefs_preextend_wal_files = false mimic: bluestore: 50-100% iops lost due to bluefs_preextend_wal_files = false Jun 15, 2019
@smithfarm smithfarm requested review from ifed01 and liewegas Jun 15, 2019
@smithfarm smithfarm added bluestore and removed core labels Jun 15, 2019
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ifed01 approved these changes Jun 17, 2019
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liewegas left a comment

let's not backport the default chagne tho

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smithfarm commented Jun 17, 2019

@ifed01 Do you know what the "default change" is?

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ifed01 commented Jun 17, 2019

@smithfarm - I think this is about default setting for bluefs_preextent_wal_size. Which has been changed to true recently, see #28322

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yuriw commented Jun 26, 2019

@yuriw yuriw merged commit f066492 into ceph:mimic Jul 1, 2019
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@smithfarm smithfarm deleted the smithfarm:wip-40280-mimic branch Aug 26, 2019
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