linux-kernel - Re: RFC: CONFIG_PAGE_SHIFT (aka software PAGE

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Date:	Thu, 12 Jul 2007 09:34:57 -0700
From:	Dave Hansen <haveblue@...ibm.com>
To:	Andrea Arcangeli <andrea@...e.de>
Cc:	David Chinner <dgc@....com>, linux-kernel@...r.kernel.org,
	David Kleikamp <shaggy@...ibm.com>
Subject: Re: RFC: CONFIG_PAGE_SHIFT (aka software PAGE_SIZE)

On Thu, 2007-07-12 at 18:31 +0200, Andrea Arcangeli wrote:
> On Fri, Jul 13, 2007 at 12:44:49AM +1000, David Chinner wrote:
> > That's crap. Just because a machine has lots of memory does not
> > make it OK to waste lots of memory.
> 
> It's not just wasted, it lowers overhead all over the place. Yes, the
> benefit of wasting less pagecache may largely outweight the benefit of
> having a larger page size, but if you've a lot of memory perhaps your
> working set already fits in the cache, or perhaps you don't fit in the
> cache regardless of the page size.

Have you guys seen Shaggy's page cache tails?

http://kernel.org/pub/linux/kernel/people/shaggy/OLS-2006/kleikamp.pdf

We've had the same memory waste issue on ppc64 with 64k hardware
pages.  

-- Dave

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