Detailed explanations for the patch:
When the small inline cache is exhausted, created a new rbtree,
and the new rbtree uses original spaces the inline nodes placed for
saving memory.
By using the rbtree can gain a better performance when nnodes gets larger.
Sorry for I doest't did much more measurements, but the average lookup time
increases slower then the original linear policy when nnodes goes larger.
For this is my first patch I submitted, I'm too excited to find something I can
hack the kernel, however I didn't consider the whole thing.
I will continue to dive into the btrfs implementation, and work harder.
:-)
- Rock
On 2012-10-4, at 下午5:44, Arne Jansen <sensi...@gmx.net> wrote:
> On 04.10.2012 11:26, David Sterba wrote:
>>> @@ -207,16 +266,23 @@ EXPORT_SYMBOL(ulist_add);
>>> * end is reached. No guarantee is made with respect to the order in which
>>> * the elements are returned. They might neither be returned in order of
>>> * addition nor in ascending order.
>>> - * It is allowed to call ulist_add during an enumeration. Newly added items
>>> - * are guaranteed to show up in the running enumeration.
>>> */
>>> struct ulist_node *ulist_next(struct ulist *ulist, struct ulist_iterator
>>> *uiter)
>>
>> Quick observation:
>>
>> If there's code relying on the behaviour stated in the removed part of
>> the comment, it will break. Have you verified this is not the case?
>
> It's a good thing to use rb-trees when the small inline cache is exhausted,
> but of course it should keep the semantics. We heavily rely on the removed
> part.
> It should be possible to keep the semantics if the elements are also kept
> in a linked list. As it inflates the size of struct ulist_node even more,
> it might make sense to use a smaller struct for the inline cache to keep
> the footprint low.
>
> Also, a commit message might be good that explains the motivation for the
> change. Have you done any measurements?
>
> Thanks for working on this.
>
> -Arne
>
>>
>>
>> david
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