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Differential D22452

Handle most object reference count updates without object locks.
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Authored by jeff on Nov 20 2019, 12:32 AM.
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kib
markj
alc
dougm
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rS355122: Use atomics in more cases for object references. We now can completely
Summary

This patch moves to only requiring the object lock on the last ref (or second to last for anonymous objects) as well as the first ref of a vnode object.

The object lock wouldn't be required for the first vnode ref except to serialize with vnode_pager_dealloc() which could race and drop a vref that is not yet acquired. I'm not sure if this is even possible anymore and if it is not vm_object_reference() could be simplified.

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Buildable 27650
Build 25856: arc lint + arc unit

Event Timeline

jeff created this revision.Nov 20 2019, 12:32 AM
Harbormaster completed remote builds in B27650: Diff 64598.Nov 20 2019, 12:32 AM
jeff retitled this revision from Experimental object reference changes to Handle most object reference count updates without object locks..Nov 20 2019, 12:40 AM
jeff edited the summary of this revision. (Show Details)
jeff added reviewers: kib, markj, alc, dougm.
jeff set the repository for this revision to rS FreeBSD src repository - subversion.
Herald added a subscriber: imp. · View Herald TranscriptNov 20 2019, 12:40 AM
jeff added inline comments.Nov 20 2019, 12:42 AM
sys/vm/vnode_pager.c
176

s/thee/the/

jeff updated this revision to Diff 64873.EditedNov 26 2019, 12:45 AM

Fix a race between unlocked reference and collapse.

This now passes various stress tests and I believe it is suitable to go in. The reduction in locking of the vnode object is substantial.

Harbormaster completed remote builds in B27770: Diff 64873.Nov 26 2019, 12:45 AM
This revision was not accepted when it landed; it landed in state Needs Review.Nov 27 2019, 12:39 AM
Closed by commit rS355122: Use atomics in more cases for object references. We now can completely (authored by jeff). · Explain Why
This revision was automatically updated to reflect the committed changes.
jeff added a commit: rS355122: Use atomics in more cases for object references. We now can completely.

Revision Contents
Changeset List

PathSize
sys/
sys/
8 lines
vm/
55 lines
24 lines

Diff 64598

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sys/sys/refcount.h

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sys/vm/vm_object.c

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sys/vm/vnode_pager.c

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