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

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Date:	Tue, 26 Jun 2012 15:45:49 +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, danielfsantos@....net
Subject: Re: [PATCH -mm v2 01/11] mm: track free size between VMAs in VMA
 rbtree

On Tue, 2012-06-26 at 09:05 -0400, Rik van Riel wrote:
> On 06/26/2012 04:31 AM, Peter Zijlstra wrote:
> 
> > If you look at your patch 1, __vma_unlink has an adjust_free_gap() right
> > next to the rb_augment_erase(), vma_adjust() has 3 adjust_free_gap()
> > calls right next to each other.
> >
> > All these will do an entire path walk back to the root. I would think we
> > could save quite a bit of updating by not having them all walk back to
> > the root. No point in re-computing the top levels if you know the next
> > update will change them again anyway.
> 
> The problem is, unless we look at the augmented data at
> rotate time, we do not know when it is safe to stop
> iterating up the tree.

argh,.. you're using adjust_vma_gap() for insertions instead of
rb_augment_insert().

I was going on the premise that you're doing updates for augmented data
without modifying the tree structure and that doing insert/delete will
keep the stuff up-to-date.

So now I'm not sure why you do if (insert) adjust_free_gap(insert),
since __insert_vm_struct(mm, insert) -> __vma_link() -> __vma_link_rb()
already does an augment update.


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