linux-kernel - Re: [RFC][PATCH 0/2] Quicklist is slighly problematic.

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Message-ID: <20080821021332.GA23397@sgi.com>
Date:	Wed, 20 Aug 2008 21:13:32 -0500
From:	Robin Holt <holt@....com>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	tokunaga.keiich@...fujitsu.com
Subject: Re: [RFC][PATCH 0/2] Quicklist is slighly problematic.

On Wed, Aug 20, 2008 at 09:10:47AM -0500, Christoph Lameter wrote:
> KOSAKI Motohiro wrote:
> > Hi Cristoph,
> > 
> > Thank you for explain your quicklist plan at OLS.
> > 
> > So, I made summary to issue of quicklist.
> > if you have a bit time, Could you please read this mail and patches?
> > And, if possible, Could you please tell me your feeling?
> 
> I believe what I said at the OLS was that quicklists are fundamentally crappy
> and should be replaced by something that works (Guess that is what you meant
> by "plan"?). Quicklists were generalized from the IA64 arch code.
> 
> Good fixup but I would think that some more radical rework is needed.
> 
> Maybe some of this needs to vanish into the TLB handling logic?
> 
> Then I have thought for awhile that the main reason that quicklists exist are
> the performance problems in the page allocator. If you can make the single
> page alloc / free pass competitive in performance with quicklists then we
> could get rid of all uses.

It is more than the free/alloc cycle, the quicklist saves us from
having to zero the page.  In a sparsely filled page table, it saves time
and cache footprint.  In a heavily used page table, you end up with a
near wash.

One problem I see is somebody got rid of the node awareness.  We used
to not put pages onto a quicklist when they were being released from a
different node than the cpu is on.  Not sure where that went.  It was
done because of the trap page problem described here.

Thanks,
Robin
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