linux-kernel - Re: [PATCH -mm v2 01/11] mm: track free size between VMAs in VMA rbtree

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Date:	Fri, 22 Jun 2012 16:37:52 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	Rik van Riel <riel@...riel.com>, linux-mm@...ck.org,
	akpm@...ux-foundation.org, aarcange@...hat.com, minchan@...il.com,
	kosaki.motohiro@...il.com, andi@...stfloor.org, hannes@...xchg.org,
	mel@....ul.ie, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm v2 01/11] mm: track free size between VMAs in VMA
 rbtree

On Fri, 2012-06-22 at 10:25 -0400, Rik van Riel wrote:
> On 06/22/2012 10:13 AM, Peter Zijlstra wrote:
> > On Fri, 2012-06-22 at 10:11 -0400, Rik van Riel wrote:
> >>
> >> I am still trying to wrap my brain around your alternative
> >> search algorithm, not sure if/how it can be combined with
> >> arbitrary address limits and alignment...
> >
> > for alignment we can do: len += align - 1;
> 
> We could, but that might lead us to returning -ENOMEM
> when we actually have memory available.
> 
> When you consider architectures like HPPA, which use
> a pretty large alignment, but align everything the same,
> chances are pretty much every freed hole will have the
> right alignment...

Well, if you don't your gap heap is next to useless and you'll revert to
simply walking all gaps until you find a suitable one.

I really worry about this search function of yours, its complexity is
very non obvious.
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