1810049 - Separate out minor GC reasons from major GC reasons

Status: NEW

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

Description

[Steve Fink [:sfink] [:s:]]

Right now, it's unclear which reasons are for a minor vs major GC. It looks like NURSERY and FULL*BUFFER are all of the minor GC reasons, and all others are major. We should consider making them contiguous in the list, even though that means they'll be totally out of order with respect to their stable IDs.

At least, I think the reasons are distinct. I looked at PREPARE_FOR_TRACING, and even though it can trigger both a minor and major GC, the minor GC will be given the reason EVICT_NURSERY.

Instead of reordering, we could add a boolean or enum to the [list of reasons(https://searchfox.org/mozilla-central/rev/b19830c6b22f73758862d34d2c64f57735890e90/js/public/GCAPI.h#568-659) that says whether it's a minor or major GC reason, even if nothing actually uses it.

(This bug came about because smaug asked in #spidermonkey which reasons are for nursery collections, and I realized there isn't a simple answer.)