1901403 - Part of GC marking in a profile doesnt appear to use more than a single thread

Status: NEW

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

Description

[Mayank Bansal]

See this profile : https://share.firefox.dev/3V8cM12
This is marking phase, and the hover pop-up shows some "GC:ParallelMarkTask" stacks. But there is no activity/use in any of the Taskcontroller threads.
(Compare this to the whole profile where taskcontroller threads do get heavily used)

Testcase is https://codepen.io/hippiefuturist/pen/NRWOxM
set number of branches to 6. Set Recursion level to 8

The reason could be as simple as "not enough work to use more than 1 thread". Feel free to INVALID.

Comment 1

[Mayank Bansal]

Attachment: about:support

Comment 2

[Mayank Bansal]

Another profile from the same testcase: https://share.firefox.dev/3Rgoky4

Comment 3

[Jon Coppeard (:jonco)]

From the support information it looks like the pref been set to use up to 8 marking threads:

javascript.options.mem.gc_max_parallel_marking_threads: 8

That's not a configuration we've tested and is definitely use at your own risk.

Having said that, there is something going wrong here.