1921908 - Optimise decommitting memory from the spare chunk

Status: RESOLVED FIXED

(Core :: Memory Allocator, enhancement)

Description

[Paul Bone [:pbone]]

In mozjemalloc when we decommit memory it may be better to decommit from the spare chunk first - since that's typically the last used memory. Also we can possibly commit multiple non-contiguous runs of pages with a single system call.

Comment 1

[Paul Bone [:pbone]]

Attachment: Bug 1921908 - pt 1. Purge from the spare chunk first r=glandium

Comment 2

[Paul Bone [:pbone]]

Attachment: Bug 1921908 - pt 2. Decommit non-contigious runs of dirty pages r=glandium

Decommit non-contigious runs of dirty pages when other free pages separate
them. For example if there are pages:

__DDDFFDFDD__

D - Dirty
F - Free
_ - other/used.

Decommit all the dirty and free pages above with a single system call.

Comment 3

[Paul Bone [:pbone]]

Attachment: Bug 1921908 - pt 3. Use else-if for mutually exclusive conditions r=glandium

Comment 4

[Paul Bone [:pbone]]

This improves "pages returned per system call" from 11.39 to 15.78, the median doesn't move as much so we can say that it's catching more outliers, but when it does it is helpful. The median time for a purge improves but I can't tell if it's significant.

Comment 5

[Paul Bone [:pbone]]

Attachment: Bug 1921908 - pt 4. Update purge stats to show extra purged pages r=glandium

Purge stats now show the number of purged and dirty pages separately.

Comment 6

[Paul Bone [:pbone]]

This has hardly any performance impact:

https://perf.compare/compare-results?baseRev=2998d9046763f701f3bc929c08a3c49997f89791&baseRepo=try&newRev=04d817974fc947759dd0f9894eccf421bb67ee02&newRepo=try&framework=13

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/6e10f95c9d5e
https://hg.mozilla.org/integration/autoland/rev/d98190178515
pt 1. Purge from the spare chunk first r=glandium
https://github.com/mozilla-firefox/firefox/commit/d27064f38160
https://hg.mozilla.org/integration/autoland/rev/0936d18965f4
pt 2. Decommit non-contigious runs of dirty pages r=glandium
https://github.com/mozilla-firefox/firefox/commit/4bfd9f914048
https://hg.mozilla.org/integration/autoland/rev/6691b36a60f7
pt 3. Use else-if for mutually exclusive conditions r=glandium
https://github.com/mozilla-firefox/firefox/commit/154eae6b87b3
https://hg.mozilla.org/integration/autoland/rev/a3c6826a7f8c
pt 4. Update purge stats to show extra purged pages r=glandium,profiler-reviewers,mstange

Comment 8

[agoloman]

https://hg.mozilla.org/mozilla-central/rev/d98190178515
https://hg.mozilla.org/mozilla-central/rev/0936d18965f4
https://hg.mozilla.org/mozilla-central/rev/6691b36a60f7
https://hg.mozilla.org/mozilla-central/rev/a3c6826a7f8c