[LU-7357] Add layout lock for striped directories.

• Type: Improvement
• Resolution: Won't Do
• Priority: Major
• Affects Version/s: Lustre 2.8.0
• Labels: dne2 dne3
• Assignee: Lai Siyao
• Reporter: James A Simmons

Description

Currently DNE2 doesn't handle layout locks to revoke the layout if it is changed. When performing an migration on a striped directory the layout lock needs to be invalidated so the client can refresh the layout.

Issue Links

• is blocking: LU-4684 DNE3: allow migrating DNE striped directory
• is related to: LU-8230 Remove "Provides: lustre-client"
• is related to: LU-6831 The ticket for tracking all DNE2 bugs
• is related to: LU-14448 lod_get_default_lov_striping() may crash for uninitialized .llc_pool
• is related to: LU-15070 client does not inherit default directory layout if changed

Comments

[Lai Siyao]

Andreas, yes, https://review.whamcloud.com/10110 can be abandoned and this can be closed.

[Andreas Dilger]

Lai, with the changes in patch https://review.whamcloud.com/45370 "LU-14448 lod: verify LOV early in lod_get_default_striping" and patch https://review.whamcloud.com/45237 "LU-15070 llite: update default LMV upon any change" is there anything left to be done here?

If not, then the patch https://review.whamcloud.com/10110 "LU-7357 lmv: add layout lock to striped directory" could be abandoned and this ticket closed.

[Lai Siyao]

Now directory layout is protected by LOOKUP lock, since directory layout is revoked only by directory migration/shrink and LFSCK layout recreate, put it under LOOKUP lock won't cause too many lock revoke.

[Lai Siyao]

Directory migration will migrate directory to a new fid, so the inode is different after migration. But there is one place that directory layout may change: after all sub files migration the parent directory will be shrunk to contain new layout only.

But I don't see the benefit of introducing this bit, because it can't eleminate race: client can't hold ibit lock, its layout can be stale at any moment with or without this bit lock. But this race is not serious, because https://review.whamcloud.com/#/c/31504/ adds rules to access migrating directory, operations through old layout may fail, but they won't corrupt the directory.

Directory layout will be updated after each lookup, getattr, setattr, setdirstripe and open, I'd say it's protected by UPDATE bit, but it's used by MDT to serialize operations, client won't clear its directory layout upon UPDATE bit revoke, because it needs layout information to access directory (just like fid), and I think we've kept it up-to-date already.

[Andreas Dilger]

Lai, is there actually a need for a separate layout bit for directory migration? Oleg thinks we can use the UPDATE bit to cancel the directory cache. Will the client get a new directory layout after that?