748454 - Use a multi-reporter for jemalloc stats

Status: RESOLVED WONTFIX

(Toolkit :: about:memory, defect)

Description

[Justin Lebar (not reading bugmail)]

Calling jemalloc_stats() is not cheap -- it locks the whole heap for a bit.  Right now, we call jemalloc_stats once for each relevant memory reporter.

This isn't important for the purposes of about:memory, but it is important inasmuch as we report numbers from jemalloc_stats() numbers in telemetry.

Comment 1

[Justin Lebar (not reading bugmail)]

I timed jemalloc stats, and one call is about .5us on my machine.  So I don't think we need to worry about this.

Comment 2

[Justin Lebar (not reading bugmail)]

(In reply to Justin Lebar [:jlebar] from comment #1)
> I timed jemalloc stats, and one call is about .5us on my machine.  So I
> don't think we need to worry about this.

(That's with a 400mb heap.)

Comment 3

[James May [:fowl2]]

(In reply to Justin Lebar [:jlebar] from comment #1)
> I timed jemalloc stats, and one call is about .5us on my machine.  So I
> don't think we need to worry about this.

What about if we're paging?

Comment 4

[Justin Lebar (not reading bugmail)]

I thought jemalloc had to iterate through each chunk in order to collect stats, but it actually iterates over all the arenas, and in our case, that's just one.  So it's actually touching very little memory.  I suspect it wouldn't be pathologically bad if we were paging.