linux-kernel - Re: [PATCH 1/2] Add trace points to mmap, munmap, and brk

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Date:	Tue, 27 Jul 2010 12:09:04 +0100
From:	Eric B Munson <emunson@...bm.net>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, mingo@...hat.com,
	hugh.dickins@...cali.co.uk, riel@...hat.com, peterz@...radead.org,
	anton@...ba.org, hch@...radead.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 1/2] Add trace points to mmap, munmap, and brk

On Wed, 21 Jul 2010, KOSAKI Motohiro wrote:

> > This patch adds trace points to mmap, munmap, and brk that will report
> > relevant addresses and sizes before each function exits successfully.
> > 
> > Signed-off-by: Eric B Munson <emunson@...bm.net>
> 
> I don't think this is good idea. if you need syscall result, you should 
> use syscall tracer. IOW, This tracepoint bring zero information.
> 
> Please see perf_event_mmap() usage. Our kernel manage adress space by
> vm_area_struct. we need to trace it if we need to know what kernel does.
> 
> Thanks.

The syscall tracer does not give you the address and size of the mmaped areas
so this does provide information above simply tracing the enter/exit points
for each call.

perf_event_mmap does provide the information for mmap calls.  Originally I sent
a patch to add a trace point to munmap and Peter Z asked for corresponding points
in the mmap family.  If the consensus is that the trace point in munmap is the
only one that should be added I can resend that patch.

-- 
Eric B Munson
IBM Linux Technology Center
ebmunson@...ibm.com

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