linux-kernel - Re: [PATCH 4/4] tracing, page-allocator: Add a postprocessing script for page-allocator-related ftrace events

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Date:	Tue, 4 Aug 2009 22:35:26 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	penberg@...helsinki.fi, a.p.zijlstra@...llo.nl, fweisbec@...il.com,
	rostedt@...dmis.org, mel@....ul.ie, lwoodman@...hat.com,
	riel@...hat.com, peterz@...radead.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 4/4] tracing, page-allocator: Add a postprocessing
	script for page-allocator-related ftrace events

* Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Tue, 4 Aug 2009 21:57:17 +0200
> Ingo Molnar <mingo@...e.hu> wrote:
> 
> > Let me demonstrate these features in action (i've applied the 
> > patches for testing to -tip):
> 
> So?  The fact that certain things can be done doesn't mean that 
> there's a demand for them, nor that anyone will _use_ this stuff.

c'mon Andrew ...

Did you never want to see whether firefox is leaking [any sort of] 
memory, and if yes, on what callsites? Try something like on an 
already running firefox context:

  perf stat -e kmem:mm_page_alloc \
            -e kmem:mm_pagevec_free \
            -e kmem:mm_page_free_direct \
     -p $(pidof firefox-bin) sleep 10

... and "perf record" for the specific callsites.

this perf stuff is immensely flexible and a very unixish 
abstraction. The perf.data contains timestamped trace entries of 
page allocations and freeing done.

[...]
> It would be nice to at least partially remove the vmstat/meminfo 
> infrastructure but I don't think we can do that?

at least meminfo is an ABI for sure - vmstat too really.

But we can stop adding new fields into obsolete, inflexible and 
clearly deficient interfaces, and we can standardize new 
instrumentation to use modern instrumentation facilities - i.e. 
tracepoints and perfcounters.

I'm not saying to put a tracepoint on every second line of the 
kernel, but obviously Mel and Rik wanted this kind of info because 
they found it useful in practice.

	Ingo
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