From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 06/13] mm: Preemptible mmu_gather
Date: Mon, 19 Apr 2010 21:16:15 +0200
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To: Nick Piggin <npiggin@suse.de>
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>, akpm@linux-foundation.org, Linus Torvalds <torvalds@linux-foundation.org>, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.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>

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.