linux-kernel - Re: [PATCH 0/3] remove kvm's use of augmented rbtree

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Date:	Mon, 10 Dec 2012 13:50:39 -0800
From:	Michel Lespinasse <walken@...gle.com>
To:	Sasha Levin <levinsasha928@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Pekka Enberg <penberg@...nel.org>,
	Asias He <asias.hejun@...il.com>, Ingo Molnar <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] remove kvm's use of augmented rbtree

On Mon, Dec 10, 2012 at 8:22 AM, Sasha Levin <levinsasha928@...il.com> wrote:
> Ping?

Hey Sasha,

There seems to have been some confusion here. After your last message,
I expected *you* to take the patches and push them towards kvm tree.
But, I guess you were waiting for Pekka's reply first ? Or did you
expect me to go push the patches ?

If it helps, I could push this through Andrew's -mm tree; however I
think it would make the most sense if these could reach linus's tree
through a kvm merge rather than through Andrew's -mm...

> On Sun, Nov 25, 2012 at 5:14 PM, Sasha Levin <levinsasha928@...il.com> wrote:
>> On Sat, Nov 24, 2012 at 9:40 PM, Michel Lespinasse <walken@...gle.com> wrote:
>>> On Thu, Nov 22, 2012 at 9:49 PM, Michel Lespinasse <walken@...gle.com> wrote:
>>>> On Thu, Nov 22, 2012 at 9:14 AM, Sasha Levin <sasha.levin@...cle.com> wrote:
>>>>> The following patch fixed the problem for me:
>>>>>
>>>>> diff --git a/include/linux/rbtree_augmented.h b/include/linux/rbtree_augmented.h
>>>>> index 214caa3..5cfdca6 100644
>>>>> --- a/include/linux/rbtree_augmented.h
>>>>> +++ b/include/linux/rbtree_augmented.h
>>>>> @@ -47,6 +47,7 @@ rb_insert_augmented(struct rb_node *node, struct rb_root *root,
>>>>>                     const struct rb_augment_callbacks *augment)
>>>>>  {
>>>>>         __rb_insert_augmented(node, root, augment->rotate);
>>>>> +       augment->propagate(node, NULL);
>>>>>  }
>>>>
>>>> This would work, but would slow down all sites which already take care
>>>> of updating the augmented information before calling
>>>> rb_insert_augmented, so please don't do that.
>>>>
>>>> The simplest fix would be to add the propagate call where your
>>>> rb_insert_augmented() call site is; the better fix would be to do the
>>>> update incrementally as you search down the tree for the insertion
>>>> point; and the best fix may be to just avoid duplicating that code and
>>>> use interval_tree.h (if your keys are longs) or
>>>> interval_tree_generic.h to generate the proper insert / remove
>>>> functions.
>>>
>>> So I had a quick look at linux-next, and my understanding is that the
>>> rbtree-interval API in kvm always stores non-overlapping intervals.
>>> Based on this, the use of augmented rbtrees isn't really justified; it
>>> is just as easy to use a simple rbtree of intervals sorted by the
>>> addresses they cover.
>>>
>>> This patchset was generated against the current linux-next. I only
>>> verified that kvm still compiled; obviously this would need more
>>> testing. On the other hand, there are currently some correctness
>>> issues in kvm's implementatin of rbtree intervals, so I think this
>>> simplification should be beneficial.
>>>
>>> Michel Lespinasse (3):
>>>   kvm: ensure non-overlapping intervals in rb_int_insert()
>>>   kvm: rb_int_search_single simplification
>>>   kvm: remove max_high field in rb_int_node structure
>>>
>>>  tools/kvm/include/kvm/rbtree-interval.h |   13 +++--
>>>  tools/kvm/util/rbtree-interval.c        |   86 ++++---------------------------
>>>  2 files changed, 18 insertions(+), 81 deletions(-)
>>>
>>> Sasha, could you please check my logic and apply this to the kvm tree ?
>>
>> When I've initially added the interval tree I figured we might need to
>> allow overlapping for future arches which might need it. Since we now
>> have extra 2 arches I guess we don't really need it. So I guess we're
>> fine with removing it.
>>
>> Pekka?
>>
>>
>> Thanks,
>> Sasha



-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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