1686219 - Investigate storing chunk metadata as a header at the start of the chunk

Status: RESOLVED FIXED

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

Description

[Jon Coppeard (:jonco)]

Currently we store all pre-chunk data as a trailer at the end of the chunk. This means the offset to this data depends on the size of the chunk. If we store it at the start then it becomes a constant. There are a bunch of hardcoded offsets like this defined in HeapAPI.h. It should also be possible have the compiler generate these for us.

Comment 1

[Jon Coppeard (:jonco)]

Attachment: Bug 1686219 - Add BitSet::SetAll and ResetAll methods r?heycam

This clears or sets every bit, taking care not to set trailing unused bits at the end of storage.

Comment 2

[Jon Coppeard (:jonco)]

Attachment: Bug 1686219 - Use mozilla::BitSet for the chunk decommit state r?sfink

Previouly this used SpiderMonkey's BitArray, but that's not public. BitSet performs the same function.

Depends on D101775

Comment 3

[Jon Coppeard (:jonco)]

Attachment: Bug 1686219 - Store chunk information at the start rather than the end of the chunk r?sfink

This moves the chunk metadata to the start of the chunk and defines the data structures in the public header. This simplifies accessing this data and removes the need for hardcoded offsets.

Requesting review from jandem for JIT updates.

Depends on D101776

Comment 4

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/cc7e6feeb95a
Add BitSet::SetAll and ResetAll methods r=heycam
https://hg.mozilla.org/integration/autoland/rev/496d47ff3fa1
Use mozilla::BitSet for the chunk decommit state r=sfink
https://hg.mozilla.org/integration/autoland/rev/43978ebfc7ac
Store chunk information at the start rather than the end of the chunk r=sfink

Comment 5

[Andreea Pavel [:apavel]]

https://hg.mozilla.org/mozilla-central/rev/cc7e6feeb95a
https://hg.mozilla.org/mozilla-central/rev/496d47ff3fa1
https://hg.mozilla.org/mozilla-central/rev/43978ebfc7ac