1991980 - Delay tracing WeakMaps until everything else is marked

Status: ASSIGNED

(Core :: JavaScript Engine, task, P2)

Description

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

Split off from bug 1935829. They're mostly independent.

WeakMap marking overhead mostly comes from the situation where a WeakMap is discovered to be reachable, but contains many live keys that have not yet been discovered to be reachable. This overhead can be reduced, sometimes dramatically, by delaying tracing the WeakMaps until everything else has been marked. At that time, the maps can be scanned and all live keys' entries traced through, and only the dead or not yet reached keys will need to be entered into the ephemeron table. This saves the time adding keys to the table that weren't reached when the map was first reached, but will be reached by the end of marking (as in, without needing to go through a WeakMap).

Note that dead keys will still be entered into the table and swept at the end, because it is unknown at map tracing time whether they are truly dead or just haven't been reached yet.

Comment 1

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

Attachment: Bug 1991980 - have GCMarker::{stop,reset} call a common GCMarker::deactivate() r=jonco

Comment 2

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

Attachment: Bug 1991980 - Reorder marking to delay tracing a WeakMap's entries until everything else has been marked r=jonco