1661888 - The profiling stack wastes 16KB of memory due to slop

Status: RESOLVED FIXED

(Core :: JavaScript Engine, enhancement, P2)

Description

[Paul Bone [:pbone]]

The code here expands the profiling stack by powers of two:

https://searchfox.org/mozilla-central/source/js/src/vm/ProfilingStack.cpp#31

But that's powers of two for the number of frames, while each frame is not a power of two. This causes allocations of 8KB when only 6KB was requested. There are 8 of these allocations in an example.com process wasting 16KB of memory.

Comment 1

[Paul Bone [:pbone]]

Attachment: Bug 1661888 - pt 1. Size the profiling stack in bytes r=jandem

Comment 2

[Paul Bone [:pbone]]

Attachment: Bug 1661888 - pt 2. Move a field to avoid padding r=jandem

Depends on D88708

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/aa156c2779c1
pt 1. Size the profiling stack in bytes r=jandem
https://hg.mozilla.org/integration/autoland/rev/97220a9e8b69
pt 2. Move a field to avoid padding r=jandem

Comment 4

[Bogdan Tara[:bogdan_tara | bogdant]]

https://hg.mozilla.org/mozilla-central/rev/aa156c2779c1
https://hg.mozilla.org/mozilla-central/rev/97220a9e8b69

Comment 5

[Florin Strugariu [:Bebe]]

== Change summary for alert #26851 (as of Wed, 02 Sep 2020 10:00:19 GMT) ==

Improvements:

6% Base Content Heap Unclassified windows10-64-shippable opt 1,555,402.00 -> 1,466,835.33
2% Heap Unclassified windows10-64-shippable opt 50,945,797.97 -> 49,691,298.62

For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=26851