From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 14/20] mm: Remove i_mmap_lock lockbreak
Date: Tue, 19 Apr 2011 13:07:19 -0700
Message-ID: <20110419130719.86093a27.akpm@linux-foundation.org>
References: <20110401121258.211963744@chello.nl>
	<20110401121725.991633993@chello.nl>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Avi Kivity <avi@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, Rik van Riel <riel@redhat.com>, Ingo Molnar <mingo@elte.hu>, Linus Torvalds <torvalds@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Benjamin Herrenschmidt <benh@kernel.crashing.org>, David Miller <davem@davemloft.net>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Mel Gorman <mel@csn.ul.ie>, Nick Piggin <npiggin@kernel.dk>, Paul McKenney <paulmck@linux.vnet.ibm.com>, Yanmin Zhang <yanmin_zhang@linux.intel.com>
List-Id: linux-arch.vger.kernel.org

On Fri, 01 Apr 2011 14:13:12 +0200
Peter Zijlstra <a.p.zijlstra@chello.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
> 
> I think the simplification of the truncate code is definately worth it.

Well, we don't need to guess.  These things are testable!

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Date: Tue, 19 Apr 2011 13:07:19 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 14/20] mm: Remove i_mmap_lock lockbreak
Message-ID: <20110419130719.86093a27.akpm@linux-foundation.org>
In-Reply-To: <20110401121725.991633993@chello.nl>
References: <20110401121258.211963744@chello.nl>
	<20110401121725.991633993@chello.nl>
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Avi Kivity <avi@redhat.com>, Thomas Gleixner <tglx@linutronix.de>, Rik van Riel <riel@redhat.com>, Ingo Molnar <mingo@elte.hu>, Linus Torvalds <torvalds@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Benjamin Herrenschmidt <benh@kernel.crashing.org>, David Miller <davem@davemloft.net>, Hugh Dickins <hugh.dickins@tiscali.co.uk>, Mel Gorman <mel@csn.ul.ie>, Nick Piggin <npiggin@kernel.dk>, Paul McKenney <paulmck@linux.vnet.ibm.com>, Yanmin Zhang <yanmin_zhang@linux.intel.com>
Message-ID: <20110419200719.hvbmRla4Ry03TLWfjJ93K1nEs8yy95QDowEl1_gSCRc@z>

On Fri, 01 Apr 2011 14:13:12 +0200
Peter Zijlstra <a.p.zijlstra@chello.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
> 
> I think the simplification of the truncate code is definately worth it.

Well, we don't need to guess.  These things are testable!