1786506 - Make Zone GC state non-atomic by moving shared permanent things to their own zone

Status: RESOLVED FIXED

(Core :: JavaScript: GC, task, P3)

Description

[Jon Coppeard (:jonco)]

Some GC things are permanent and shared between runtimes. They are allocated in the parent runtime's atoms zone and may be referred to by child runtimes. This means that any GC by child runtimes must be able to detect and ignore them.

One way this happens currently is by marking all these shared things black on initialisation and never collecting them. This helps cases where we check a GC thing's mark state. They are still part of the parent runtime's atoms zone though, and the state of this zone can change independently of child runtimes. This means that (at least) the zone state must be atomic to avoid races.

Instead of this, we can allocate these things into their own separate zone. This will not be collected until shutdown and so we won't get any races checking the state. The compiler can generate more efficient code for checking the state, and we can also merge most checks for shared things with existing zone state checks.

Comment 1

[Jon Coppeard (:jonco)]

Attachment: Bug 1786506 - Part 1: Add ZoneList prepend operation and use move semantics to indicate argument list is consumed r?sfink

Comment 2

[Jon Coppeard (:jonco)]

Attachment: Bug 1786506 - Part 2: Give shared permanent things their own zone r?sfink

Depends on D155377

Comment 3

[Jon Coppeard (:jonco)]

Attachment: Bug 1786506 - Part 3: Make Zone GC state non-atomic r?sfink

Depends on D155378

Comment 4

[Jon Coppeard (:jonco)]

Attachment: Bug 1786506 - Part 4: Remove checks for GC things owned by other runtimes where possible r?sfink

Depends on D155379

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/747154213937
Part 1: Add ZoneList prepend operation and use move semantics to indicate argument list is consumed r=sfink
https://hg.mozilla.org/integration/autoland/rev/73928903648a
Part 2: Give shared permanent things their own zone r=sfink
https://hg.mozilla.org/integration/autoland/rev/1f7a816e0141
Part 3: Make Zone GC state non-atomic r=sfink
https://hg.mozilla.org/integration/autoland/rev/dcf78df2531b
Part 4: Remove checks for GC things owned by other runtimes where possible r=sfink

Comment 6

[Sandor Molnar[:smolnar]]

https://hg.mozilla.org/mozilla-central/rev/747154213937
https://hg.mozilla.org/mozilla-central/rev/73928903648a
https://hg.mozilla.org/mozilla-central/rev/1f7a816e0141
https://hg.mozilla.org/mozilla-central/rev/dcf78df2531b

Comment 7

[Andrej (:aglavic)]

== Change summary for alert #35236 (as of Mon, 29 Aug 2022 23:17:57 GMT) ==

Improvements:

Ratio	Test	Platform	Options	Absolute values (old vs new)
7%	dromaeo_dom	linux1804-64-shippable-qr	e10s fission stylo webrender	2,708.04 -> 2,904.33
7%	dromaeo_dom	linux1804-64-shippable-qr	e10s fission stylo webrender	2,712.22 -> 2,890.48

For up to date results, see: https://treeherder.mozilla.org/perfherder/alerts?id=35236