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

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Date:	Tue, 03 Jul 2012 17:37:46 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Michel Lespinasse <walken@...gle.com>
CC:	Rik van Riel <riel@...riel.com>, linux-mm@...ck.org,
	akpm@...ux-foundation.org, aarcange@...hat.com,
	peterz@...radead.org, 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 06/29/2012 07:46 PM, Michel Lespinasse wrote:

I have the free_gap(node) function now.

>>   	rb_link_node(&vma->vm_rb, rb_parent, rb_link);
>>   	rb_insert_color(&vma->vm_rb,&mm->mm_rb);
>> +	adjust_free_gap(vma);
>> +	/* Propagate the new free gap between next and us up the tree. */
>> +	if (vma->vm_next)
>> +		adjust_free_gap(vma->vm_next);
>>   }
>
> So this will work, and may be fine for a first implementation. However,
> the augmented rbtree support really seems inadequate here. What we
> would want is for adjust_free_gap to adjust the node's free_gap as
> well as its parents, and *stop* when it reaches a node that already
> has the desired free_gap instead of going all the way to the root as
> it does now. But, to do that we would also need rb_insert_color() to
> adjust free_gap as needed when doing tree rotations, and it doesn't
> have the necessary support there.
>
> Basically, I think lib/rbtree.c should provide augmented rbtree support
> in the form of (versions of) rb_insert_color() and rb_erase() being able to
> callback to adjust the augmented node information around tree rotations,
> instead of using (conservative, overkill) loops to adjust the augmented
> node information after the fact

That is what I originally worked on.

I threw out that code after people told me (at LSF/MM) in
no uncertain terms that I should use the augmented rbtree
code :)

Will CC you on the next version.

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