linux-kernel - Re: HOLES_IN

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Date:	Fri, 6 Feb 2009 08:59:45 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	mel@....ul.ie, kamezawa.hiroyu@...fujitsu.com,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	sparclinux@...r.kernel.org
Subject: Re: HOLES_IN_ZONE...

On Thu, 05 Feb 2009 15:44:03 -0800 (PST)
David Miller <davem@...emloft.net> wrote:

> > Later I reduced MAX_ORDER to 9 on s390, so we don't leave large
> > portions of memory unused.
> 
> Isn't is easier to just make sure your vmemmap mappings extend to such
> boundaries, whether they contain available memory or not?
> 
> That's the only requirement you have to satisfy to avoid having to
> specify HOLES_IN_ZONE.  You don't have to have memory there, just
> some vmmemmap page structs have to be mapped at those indices.
> 
> And then you won't need waste memory with these MAX_ORDER boundary
> adjustments.

Sounds reasonable. Back then I was under the impression that it is not
sufficient to only have a struct page but also a page for each PFN.
I'll give it a try as soon as time permits.

Thanks!
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