770110 - GC: gcIncrementalState is now used by non-incremental GCs

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jon Coppeard (:jonco) (PTO until 3rd April)]

It used to be the case that JSRuntime::gcIncrementalState == NO_INCREMENTAL implied a non-incremental GC was taking place.

Following the fix for bug 763984, gcIncrementalState is used even when doing a non-incremental GC, so this is no longer true.

A couple of places where this test is made should be updated.

This doesn't affect the final behaviour of the GC, but does mean that for non-incremental GCs JIT code is discarded twice and ValidateIncrementalMarking is called unnecessarily.

Comment 1

[Jon Coppeard (:jonco) (PTO until 3rd April)]

Attachment: Correct tests of gcIncrementalState

Comment 2

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

Comment on attachment 638288 [details] [diff] [review]
Correct tests of gcIncrementalState

Review of attachment 638288 [details] [diff] [review]:
-----------------------------------------------------------------

This basically looks good.

::: js/src/jsgc.cpp
@@ +3582,5 @@
>  #endif
>  
> +    bool isIncremental = budget != SliceBudget::Unlimited ||
> +        zeal == ZealIncrementalRootsThenFinish ||
> +        zeal == ZealIncrementalMarkAllThenFinish;

I don't think this is quite right. If we're in the last slice of an incremental GC, the budget can be set to Unlimited. Maybe you want to add a condition || rt->gcIncrementalState != NO_INCREMENTAL.

Also, the second and third lines should be indented so that zeal lines up with budget.

Comment 3

[Jon Coppeard (:jonco) (PTO until 3rd April)]

Attachment: Update with review comments and fix assertion issue

Comment 4

[Jon Coppeard (:jonco) (PTO until 3rd April)]

The original patch cased assertion failures on the try build - JS_ROOT_MARKING_ASSERT was going off because roots can be marked when gcIncrementalState == NO_INCREMENTAL, when called either from ValidateIncrementalMarking or TraceRuntime.  The updated patch should fix this (currently trying again).

Comment 5

[Jon Coppeard (:jonco) (PTO until 3rd April)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/df79a01137c1

Comment 6

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/df79a01137c1