linux-kernel - Re: [PATCH 06/13] mm: Preemptible mmu

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Date:	Mon, 19 Apr 2010 21:16:15 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Nick Piggin <npiggin@...e.de>
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,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Mel Gorman <mel@....ul.ie>
Subject: Re: [PATCH 06/13] mm: Preemptible mmu_gather

On Fri, 2010-04-09 at 22:36 +0200, Peter Zijlstra wrote:
> On Fri, 2010-04-09 at 13:25 +1000, Nick Piggin wrote:
> > Have you done some profiling on this? What I would like to see, if
> > it's not too much complexity, is to have a small set of pages to
> > handle common size frees, and then use them up first by default
> > before attempting to allocate more.
> > 
> > Also, it would be cool to be able to chain allocations to avoid
> > TLB flushes even on big frees (overridable by arch of course, in
> > case they're doing some non-preeemptible work or you wish to break
> > up lock hold times). But that might be just getting over engineered.

[ patch to do very long queues ]

One thing that comes from having preemptible mmu_gather, and esp. when
we allow such very long gathers, is that we can potentially have a very
large amount of pages stuck on these lists.

So we'd need to hook into reclaim somehow to allow flushing of them when
we're falling short.

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