From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [RFC v1][PATCH]page_fault retry with NOPAGE_RETRY
Cc: kosaki.motohiro@jp.fujitsu.com, Mike Waychison <mikew@google.com>,
       Nick Piggin <npiggin@suse.de>, Ying Han <yinghan@google.com>,
       Ingo Molnar <mingo@elte.hu>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org, akpm <akpm@linux-foundation.org>,
       David Rientjes <rientjes@google.com>, Rohit Seth <rohitseth@google.com>,
       Hugh Dickins <hugh@veritas.com>, "H. Peter Anvin" <hpa@zytor.com>,
       edwintorok@gmail.com
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Date: Thu, 27 Nov 2008 20:08:29 +0900 (JST)
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> Furthermore, /proc code usually isn't written with performance in mind,
> so its usually simple and robust code. Adding it to a 'hot'-path like
> you're doing doesn't seem advisable.
> 
> Also, releasing and re-acquiring mmap_sem can significantly add to the
> cacheline bouncing that thing already has.

Interesting.

I tryed to demonstration /proc slowness.

1. make many process
	$ nice ./hackbench 120 process 10000

2. read /proc
	$ time ps -ef

	0.16s user 0.57s system 1% cpu 46.859 total


HAHAHA!
That is really slow over my expected.


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