linux-kernel - Re: quicklists confuse meminfo

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Message-Id: <200803111507.20870.nickpiggin@yahoo.com.au>
Date:	Tue, 11 Mar 2008 15:07:20 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Bart Van Assche <bart.vanassche@...il.com>
Subject: Re: quicklists confuse meminfo

On Tuesday 11 March 2008 02:54, Christoph Lameter wrote:
> On Sun, 9 Mar 2008, Andrew Morton wrote:
> > - They are pretty marginal from a performance POV (iirc)
>
> Pretty significant in our experience.
>
> >   Making __GFP_ZERO smarter/more efficient would be a preferable way of
> >   addressing any performance problems we have in there.
>
> Looking at the page allocator "fastpath": The basic reaons that this was
> such a good optimization was that the page allocator is expensive to call.
> The hotpath gets more and more clogged with logic. Fixing the page
> allocator to be more efficient may be the right approach here. That could
> also include having a list of zeroed pages.

This is insane. We add more and more of this NUMA and cpuset and anti-frag
and page zeroing logic to the page allocator, and then decide that we
don't actually need to obey any of those rules when we're running lat_proc.

You will never be able to make the page allocator faster than a single list
of pages. The reason is because we actually *want* some of these checks and
heuristics in the page allocator.

And I doubt a list of zeroed pages is the right approach. That's just
adding more complexity for lat_proc AFAIKS.


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