Page MenuHomeFreeBSD
Differential D22636

Weaken three asserts in preparation for lock pushdown in fault.
ClosedPublic
Actions

Authored by jeff on Dec 2 2019, 11:47 PM.
Tags
None
Referenced Files
Unknown Object (File)
Wed, Jul 29, 12:26 AM
Unknown Object (File)
Mon, Jul 27, 1:59 AM
Unknown Object (File)
Thu, Jul 23, 4:09 PM
Unknown Object (File)
Wed, Jul 22, 1:42 AM
Unknown Object (File)
Sun, Jul 19, 8:52 PM
Unknown Object (File)
Sat, Jul 18, 2:25 AM
Unknown Object (File)
Thu, Jul 16, 7:19 PM
Unknown Object (File)
Sat, Jul 11, 11:32 AM
View All Files
Subscribers
imp

Details

Reviewers
alc
doug_freebsd.con.com
kib
markj
Commits
rS355516: It is safe to wire a page while the object is busy.
rS355515: It is now safe to rename a page that is still on a queue. Allowing this
rS355514: Do not assert that the object lock is held in vm_object_set_writeable_dirty.
Summary

I believe vfs_set_writeable_dirty is safe without an object lock at all. I originally had it required to keep the type stable but it does not matter if we race with dead and that would be a reference bug.

Mark tells me that I can now vm_page_replace() while a page is in queue. This allows me to optimize fault in two ways. Firstly, we allocate and free a page in first_object every time we discover a busy backing object page. We only need to do this once and leave it invalid but in a paging queue. the cow optimization replace runs into this. Secondly, this allows me to skip requiring the first_object write lock in cases where we want to free the page.

Lastly, vm_object_busy() is a standin for xbusy. Allow wired refs while the object is busy.

Diff Detail

Lint
Lint Passed
Unit
No Test Coverage
Build Status
Buildable 27898
Build 26069: arc lint + arc unit

Event Timeline

jeff created this revision.Dec 2 2019, 11:47 PM
Harbormaster completed remote builds in B27898: Diff 65145.Dec 2 2019, 11:47 PM
jeff edited the summary of this revision. (Show Details)Dec 2 2019, 11:51 PM
jeff added reviewers: alc, doug_freebsd.con.com, kib, markj.
jeff set the repository for this revision to rS FreeBSD src repository - subversion.
Herald added a subscriber: imp. · View Herald TranscriptDec 2 2019, 11:51 PM
markj added inline comments.Dec 3 2019, 3:32 PM
sys/vm/vm_object.c
2228

Can we instead assert that object->ref_count > 0?

sys/vm/vm_page.c
1692

As you noted, I think this is fine. The assertion was added in r331128 but the reasoning given in the commit message no longer applies: the page daemon now handles pages without an object (by ignoring them).

3774

This should be fine now that xbusy is treated as a proper lock.

kib accepted this revision.Dec 3 2019, 3:39 PM
This revision is now accepted and ready to land.Dec 3 2019, 3:39 PM
jeff added inline comments.Dec 3 2019, 5:52 PM
sys/vm/vm_object.c
2228

yes, I think that's reasonable.

markj accepted this revision.Dec 3 2019, 7:49 PM
Closed by commit rS355514: Do not assert that the object lock is held in vm_object_set_writeable_dirty. (authored by jeff). · Explain WhyDec 8 2019, 1:48 AM
This revision was automatically updated to reflect the committed changes.
jeff added a commit: rS355514: Do not assert that the object lock is held in vm_object_set_writeable_dirty..
jeff added a commit: rS355515: It is now safe to rename a page that is still on a queue. Allowing this.
jeff added a commit: rS355516: It is safe to wire a page while the object is busy..Dec 8 2019, 1:50 AM

Revision Contents
Changeset List

PathSize
sys/
vm/
2 lines
4 lines

Diff 65145

View Options

sys/vm/vm_object.c

Loading...
View Options

sys/vm/vm_page.c

Loading...