linux-kernel - Re: malloc() tracing in perf?

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Date:	Thu, 06 Aug 2009 12:19:04 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC:	Ingo Molnar <mingo@...e.hu>, acme <acme@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Frédéric Weisbecker" <fweisbec@...il.com>,
	Eduard-Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
	roland <roland@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	fche <fche@...hat.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: malloc() tracing in perf?

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
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