linux-kernel - Re: larger default page sizes...

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Message-ID: <Pine.LNX.4.64.0803251045510.16206@schroedinger.engr.sgi.com>
Date:	Tue, 25 Mar 2008 10:48:19 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	David Miller <davem@...emloft.net>
cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-ia64@...r.kernel.org, torvalds@...ux-foundation.org
Subject: Re: larger default page sizes...

On Mon, 24 Mar 2008, David Miller wrote:

> We should fix the underlying problems.
> 
> I'm hitting issues on 128 cpu Niagara2 boxes, and it's all fundamental
> stuff like contention on the per-zone page allocator locks.
> 
> Which is very fixable, without going to larger pages.

No its not fixable. You are doing linear optimizations to a slowdown that 
grows exponentially. Going just one order up for page size reduces the
necessary locks and handling of the kernel by 50%.
 
> > powerpc also runs HPC codes. They certainly see the same results
> > that we see.
> 
> There are ways to get large pages into the process address space for
> compute bound tasks, without suffering the well known negative side
> effects of using larger pages for everything.

These hacks have limitations. F.e. they do not deal with I/O and 
require application changes.
 
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