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

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Date:	Fri, 3 Sep 2010 08:09:27 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Eric B Munson <emunson@...bm.net>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	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


* Eric B Munson <emunson@...bm.net> wrote:

> Sorry for the long delay, the enter/exit routines are not compatible 
> with the information that these new trace points provides.  When 
> tracing mmap, for instance, the addr and len arguments can be altered 
> by the function.  If you use the enter/exit trace points you would not 
> see this as the arguments are sampled at function entrance and not 
> given again on exit.  Also, the new trace points are only hit on 
> function success, the exit trace point happens any time you leave the 
> system call.

Would it be feasible to use enter/exit information as the main source of 
events - and only add new tracepoints for the _missing_ information? 
(such as when mmap arguments change)

Then user-space can combine the two. The new tracepoints would also 
carry useful information in themselves: they would show the cases where 
user-space did not get what it wished. (or so)

Thanks,

	Ingo
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