linux-kernel - Re: [PATCH 4/4] IA64: SPARSE_VIRTUAL 16M page size support

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Date:	Thu, 05 Apr 2007 16:10:27 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	tony.luck@...el.com
Cc:	clameter@....com, akpm@...ux-foundation.org,
	linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org,
	mbligh@...gle.com, linux-mm@...ck.org, ak@...e.de,
	hansendc@...ibm.com, kamezawa.hiroyu@...fujitsu.com
Subject: Re: [PATCH 4/4] IA64: SPARSE_VIRTUAL 16M page size support

From: "Luck, Tony" <tony.luck@...el.com>
Date: Thu, 5 Apr 2007 15:50:02 -0700

> Maybe a granule is not the right unit of allocation ... perhaps 4M
> would work better (4M/56 ~= 75000 pages ~= 1.1G)?  But if this is
> too small, then a hard-coded 16M would be better than a granule,
> because 64M is (IMHO) too big.

A 4MB chunk of page structs covers about 512MB of ram (I'm rounding up
to 64-bytes in my calculations and using an 8K page size, sorry :-).
So I think that is too small although on the sparc64 side that is the
biggest I have available on most processor models.

But I do agree that 64MB is way too big and 16MB is a good compromise
chunk size for this stuff.  That covers about 2GB of ram with the
above parameters, which should be about right.
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