1614875 - Tune some PHC knobs

Status: RESOLVED FIXED

(Core :: Memory Allocator, enhancement)

Description

[Nicholas Nethercote [inactive]]

PHC has a bunch of knobs that affect allocation and recycling rates. They're currently not set very well -- the allocation rate is too high, which leads to early slot saturation, and the recycling speed is too fast, which leads to incorrect stacks in crash reports.

Comment 1

[Nicholas Nethercote [inactive]]

Attachment: Bug 1614875 - Gather more stats in PHC. r=glandium

Specifically, the number of page allocs in use, and the page alloc hit rate.

Comment 2

[Nicholas Nethercote [inactive]]

Attachment: Bug 1614875 - Tweak constants to prevent saturation and improve the hit rate. r=glandium

With the old constants the page alloc slots would fill up quickly and the hit
rate would quickly drop below 20%.

With the new constants the alloc slots don't fill up so quickly and the hit
rate remains at or near 100% for a lot longer. Also, page allocs are recycled
more slowly, which should decrease the likelihood of incorrect alloc/free stack
traces in reported crashes.

Depends on D62538

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/c41dc66209f6
Gather more stats in PHC. r=glandium
https://hg.mozilla.org/integration/autoland/rev/81d380c3ec9e
Tweak constants to prevent saturation and improve the hit rate. r=glandium

Comment 4

[Nicholas Nethercote [inactive]]

Comment on attachment 9126019 [details]
Bug 1614875 - Gather more stats in PHC. r=glandium

Beta/Release Uplift Approval Request

• User impact if declined: These simple commits tweak PHC's parameters, which will hopefully make it more effective at detecting UAFs. They also include some simple stats-gathering that informed the parameter tweaking.

PHC is only enabled in early beta so if they don't get uplifted we will have to wait until the next release cycle to evaluate the new parameters.

• Is this code covered by automated tests?: Yes
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Just tweaks some existing parameters and adds a tiny bit of stats-gathering code, which isn't even used by default because you need to compile with PHC_LOGGING = 1 to see the stats, and we ship with PHC_LOGGING = 0.
• String changes made/needed: None

Comment 5

[Cristian Brindusan [:cbrindusan]]

https://hg.mozilla.org/mozilla-central/rev/c41dc66209f6
https://hg.mozilla.org/mozilla-central/rev/81d380c3ec9e

Comment 6

[Ryan VanderMeulen [:RyanVM]]

Comment on attachment 9126019 [details]
Bug 1614875 - Gather more stats in PHC. r=glandium

PHC improvements. Approved for 74.0b3 so we can get feedback sooner.

Comment 7

[Oana Pop-Rus]

https://hg.mozilla.org/releases/mozilla-beta/rev/9bb03e64a368
https://hg.mozilla.org/releases/mozilla-beta/rev/54b5788b78a9