[LU-15252] option to disable LSOM updates

• Type: Improvement
• Resolution: Fixed
• Priority: Major
• Fix Version/s: Lustre 2.15.0
• Affects Version/s: Lustre 2.15.0
• Labels: patch
• Assignee: Alexander Boyko
• Reporter: Alexander Boyko

Description

When LSOM is not used at cluster it is better to disable it, I don't see such option for now.
During analyze of MDS vmocre with high load avarage, we have found LSOM feature add big impact to it.
205 threads were blocked with mdt_lsom_update(). A few threads got further and were waiting for the osd lock for read. It seems that mdt_lsom_update() has a serious issue with a single shared file because of its mdt-level mutex for every close request.

Comments

[Gerrit Updater]

"Oleg Drokin <[e-mail]>" merged in patch https://review.whamcloud.com/45709/
Subject: LU-15252 mdt: reduce contention at mdt_lsom_update
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: c8b7afe4970415f8dae84f5e20661f8a3b3681a0

[Andreas Dilger]

Still a second patch in flight that fixes the performance issue instead of working around it.

[Peter Jones]

Landed for 2.15

[Gerrit Updater]

"Oleg Drokin <[e-mail]>" merged in patch https://review.whamcloud.com/45619/
Subject: LU-15252 mdc: add client tunable to disable LSOM update
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: 19172ed37851fdd5731b1319c12151f5cb1fe267

[Gerrit Updater]

"Alexander Boyko <[e-mail]>" uploaded a new patch: https://review.whamcloud.com/45709
Subject: LU-15252 mdt: reduce contention at mdt_lsom_update
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: 495a7eb370cf9dbb5eec67bbd0a59ae206cdb68a

[Andreas Dilger]

aboyko, I think the LSOM update can be fairly lazy, and there isn't a serious danger if some updates are lost, but there should still be occasional writes of new LSOM data to disk:

• if the inode is being written already for some other reason (e.g. atime update, link count, etc.)
• after some long time since the last LSOM update (e.g. 60s, like atime_diff). maybe LSOM and atime writes will happen at the same time?
• when the last client closes the file, including when the client is evicted

My main concern would be that files which are never properly closed will also never get LSOM updates. That could happen with config files or shared libraries for jobs that run a very long time, and/or files that are being accessed by different jobs and always have some client process holding them open.