Investigating making permanent GC things always black
Categories
(Core :: JavaScript: GC, task, P3)
Tracking
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| Tracking | Status | |
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| firefox95 | --- | fixed |
People
(Reporter: jonco, Assigned: jonco)
References
Details
Attachments
(4 files)
It would be great if we could arrange for permanent GC things (that may be shared between runtimes) to always be black and never have their mark bits cleared. That way, we could remove the checks for permanent GC things that often occur next to a check for whether the thing is marked, since we have to do the mark check anyway.
We already did this for permanent atoms in bug 1669669. We'd need to do the same for well-known symbols. I'm not sure whether other permanent things in the atoms zone (e.g. JIT stubs) can be shared.
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Updated•3 years ago
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Comment 1•3 years ago
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In the same way as we freeze permanent atoms on startup we can freeze
well-known sybols too. This has the following advantages
- we don't have to mark them
- we don't have to sweep them
- we can now assume that permanent and potentially shared things are always marked
Depends on D129287
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Comment 2•3 years ago
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Anything owned by another runtime will always be marked black so we can fold
this check into the existing check for whether a thing is marked.
Depends on D129288
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Comment 3•3 years ago
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Some places check a thing's zone's GC state before checking its mark bits. To
make this safe the GC state needs to be atomic. The outcome of these checks is
independent of the zone GC state observed.
Depends on D129289
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Comment 4•3 years ago
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These checks are replaced by assertions that the thing is black if it's owned
by another runtime, and hence we will return the right result.
Depends on D129290
Pushed by jcoppeard@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/cea53a626528 Part 1: Freeze well-known symbols on engine initialization r=sfink https://hg.mozilla.org/integration/autoland/rev/dcc7bbf8b0da Part 2: Remove checks for things owned by other runtimes when marking r=sfink https://hg.mozilla.org/integration/autoland/rev/068545b6f978 Part 3: Make zone GC state atomic to make it safe to observe from other runtimes r=sfink https://hg.mozilla.org/integration/autoland/rev/0d7c0ebe0e3c Part 4: Remove checks for things owned by other runtimes in IsMarked, IsAboutToBeFinalized and SweepingTracer r=sfink
Pushed by jcoppeard@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/4df5a0d025f9 Part 1: Freeze well-known symbols on engine initialization r=sfink https://hg.mozilla.org/integration/autoland/rev/85f439d1507d Part 2: Remove checks for things owned by other runtimes when marking r=sfink https://hg.mozilla.org/integration/autoland/rev/5ccc1dafb61e Part 3: Make zone GC state atomic to make it safe to observe from other runtimes r=sfink https://hg.mozilla.org/integration/autoland/rev/cd76a8234de6 Part 4: Remove checks for things owned by other runtimes in IsMarked, IsAboutToBeFinalized and SweepingTracer r=sfink
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Comment 8•3 years ago
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| bugherder | ||
https://hg.mozilla.org/mozilla-central/rev/4df5a0d025f9
https://hg.mozilla.org/mozilla-central/rev/85f439d1507d
https://hg.mozilla.org/mozilla-central/rev/5ccc1dafb61e
https://hg.mozilla.org/mozilla-central/rev/cd76a8234de6
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Assignee | |
Updated•3 years ago
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Description
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