linux-kernel - Re: [PATCH 2/8] mm: Remove i_mmap

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Message-Id: <20110218024603.2089221d.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 18 Feb 2011 02:46:03 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rik van Riel <riel@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	akpm@...ux-foundation.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-mm@...ck.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
Subject: Re: [PATCH 2/8] mm: Remove i_mmap_mutex lockbreak

On Thu, 17 Feb 2011 18:05:22 +0100
Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> Hugh says:
>  "The only significant loser, I think, would be page reclaim (when
>   concurrent with truncation): could spin for a long time waiting for
>   the i_mmap_mutex it expects would soon be dropped? "
> 
> Counter points:
>  - cpu contention makes the spin stop (need_resched())
>  - zap pages should be freeing pages at a higher rate than reclaim
>    ever can
>  - shouldn't hold up reclaim more than lock_page() would
> 
> I think the simplification of the truncate code is definately worth
> it.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>

Maybe I have to improve batched-uncharge in memcg, whose work depends
on ZAP_BLOCK_SIZE....but the zap routine seems cleaner.

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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