2041420 - Closed chrome windows are kept alive across mochitests until a shrinking GC runs

Status: NEW

(Core :: JavaScript Engine: JIT, defect, P2)

Description

[Florian Quèze [:florian]]

Bug 2040924 worked around a problem where, when mochitests run back-to-back, closed chrome windows accumulate until shutdown, driving up CC times and consuming memory in CI. Investigation suggested JIT/IC stubs on hot shared chrome scripts were holding references that kept these windows alive across tests.

The workaround in bug 2040924 forces a shrinking GC + CC between mochitests, which clears them. In normal Firefox use, the automatic idle-driven shrinking GC should handles this.

Filing this per review feedback so the JIT team can investigate the underlying behavior.

To reproduce, undo the hack from bug 2040924 then run the tests in the browser/components/aiwindow/ui/test/browser/ folder (which is where there is the most pain currently, ie bug 1984528). The ever increasing memory use will be visible in the memory track of the resource usage profile (that you can see with mach resource-usage when running tests locally). To make the issue more visible, you can also apply patches from bug 2040929.