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

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Message-Id: <20100712104602.EA1A.A69D9226@jp.fujitsu.com>
Date:	Mon, 12 Jul 2010 10:58:01 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	kosaki.motohiro@...fujitsu.com, Eric B Munson <emunson@...bm.net>,
	akpm@...ux-foundation.org, mingo@...hat.com,
	hugh.dickins@...cali.co.uk, riel@...hat.com, peterz@...radead.org,
	anton@...ba.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] Add trace events to mmap and brk

> Hmm, thinking about it a bit more, what do you trace events give us that
> the event based syscall tracer doesn't?

Yup. I think we need two tracepoint.

 1) need to know userland argument.
    -> syscall tracer
 2) need to know actual vma change.
    -> need to trace more low layer


As I said, if userland app have following code,

	mmap(0x10000, PROT_READ|PROT_WRITE)
	mmap(0x10000, PROT_NONE)

second mmap implicitly unmap firt mmap region and map another region.
so if we want to track munmap activity, syscall exiting point is not
so good place. we need to trace per-vma activity.

btw, perf_event_mmap() already take vma argument.





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