linux-kernel - Re: [RFC v1][PATCH]page_fault retry with NOPAGE

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Message-Id: <20081127200501.3CF9.KOSAKI.MOTOHIRO@jp.fujitsu.com>
Date:	Thu, 27 Nov 2008 20:08:29 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	kosaki.motohiro@...fujitsu.com, Mike Waychison <mikew@...gle.com>,
	Nick Piggin <npiggin@...e.de>, Ying Han <yinghan@...gle.com>,
	Ingo Molnar <mingo@...e.hu>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, akpm <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Rohit Seth <rohitseth@...gle.com>,
	Hugh Dickins <hugh@...itas.com>,
	"H. Peter Anvin" <hpa@...or.com>, edwintorok@...il.com
Subject: Re: [RFC v1][PATCH]page_fault retry with NOPAGE_RETRY

> 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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