887929 - GC: decommit unused chunks in the background

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Terrence Cole [:terrence]]

Currently, when a Chunk becomes empty, it gets added to a list of free chunks and only freed if it does not get re-used within the next two GC's. On memory constrained systems such as android and B2G, keeping this memory alive and committed can result in OOM through C allocations that cannot use our GC heap. We should simply decommit any chunks that are waiting in this list so that their backing physical memory can be re-used by other allocations in the system.

This should be a less costly, but more complex, solution to the problem that Bug 887652 also solves.

Comment 1

[Terrence Cole [:terrence]]

This happened either when we moved everything to ChunkPool or during the decommit-on-the-background: I don't remember. In any case, we assert that it is true in every GC:

http://searchfox.org/mozilla-central/rev/064025c802c22cd5ad122746733cbd34ea47393c/js/src/jsgc.cpp#3117-3119