Re: Possible inline malloc alternatives: bitmap

[Carlos O'Donell <carlos@redhat.com>]

On 03/03/2018 12:24 PM, Paul Eggert wrote:
> I didn't quite follow your profiling proposals. As near as I can make
> out you'd like to log calls to malloc, free, etc. But for good
> results don't you also need to log memory accesses? Otherwise how
> will you know which objects are hot?

We can already log malloc, free, etc. with the inlined tracing code we
have on DJ's branch, and we in turn simulate those traces again.

You only need to log memory accesses if you want perfect reconstruction
of the various memory subsystem effects. As you know this is obviously
very expensive and difficult if not impossible to do. Some suggestions
at LPC were provided though, including tracking heuristics or statistical
profiles of hits/misses and trying to recreate those profiles in the
page-touch heuristics used by the simulator (something it does when it
gets a new block of memory).

Today we mostly use the simulator to look at in-use RSS, RSS max,
and external and internal fragmentation, looking at trying to reduce
that as much as we can.

Actually using it for profile driven feedback is very hard, and that
kind of behaviour seems to be largely derived from first principles
in most academic work.

-- 
Cheers,
Carlos.