Re: malloc() tracing in perf?

Pekka Enberg
2009-08-06T09:19:09Z

Pekka Enberg wrote:
> Hi Peter,
>
> On Thu, 2009-08-06 at 10:48 +0300, Pekka Enberg wrote:
>>> Hi,
>>>
>>> It's me again :-).
>>>
>>> I have a little user-space application that is pretty memory hungry
>>> and I want to understand why. I started to google around for a memory
>>> profiler or a malloc() tracer but didn't seem to find anything really
>>> useful.
>>>
>>> But then it hit me, why can't I have kmemtrace + perf but for
>>> user-space? Something like the "Malloc Trace" shown here:
>>>
>>> http://developer.apple.com/documentation/developertools/conceptual/SharkUserGuide/OtherProfilingandTracingTechniques/OtherProfilingandTracingTechniques.html#//apple_ref/doc/uid/TP40005233-CH6-SW17
>>>
>>>
>>> Does this sound like something that could/should be part of "perf"?
>>> How would all this work anyway? Can we intercept malloc() and free()
>>> somehow? Where would the data be pushed? Am I just going perf-crazy
>>> and trying to turn it into a swiss army knife because it's so easy to
>>> use?-)
>
> Peter Zijlstra wrote:
>> OK, you just trod into a wasp's nest :-)
>>
>> That sounds like uprobes, the equivalent of kprobes but for userspace.
>>
>> I seem to have heard people are working on such a thing, but I can't
>> seem to find a single LKML post with 'uprobe' in the subject in the past
>> two years or something (except for MTUprobe) -- so I guess its not
>> really going anywhere any fast.
>
> [snip]
>
> Right. Are dynamic tracepoints what we want for malloc() and free()
> interception, though? I guess we can just do generic "userspace function
> called" events and record the passed parameters. Then "perf memreport"
> can just go find all the malloc() and free() calls and construct a
> memory profile out of it?
>
> That said, I'd also be interested in wiring my userspace VM garbage
> collector to emit similar alloc and free events as well (because perf
> already has a JIT symbol map) which makes me think we want generic
> "userspace allocated memory" events.

Argh, I dropped LKML from the CC. Sorry for the duplicate email!

Pekka