[PATCH 0/3] remove kvm's use of augmented rbtree

[Michel Lespinasse]

On Thu, Nov 22, 2012 at 9:49 PM, Michel Lespinasse <walken@xxxxxxxxxx> wrote:
> On Thu, Nov 22, 2012 at 9:14 AM, Sasha Levin <sasha.levin@xxxxxxxxxx> 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 ?

Thanks,

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