Re: [PATCH v4] drivers/base/memory.c: cache blocks in radix tree to accelerate lookup

David Hildenbrand
2020-01-16T15:28:19Z

On 16.01.20 16:22, Michal Hocko wrote:
> On Wed 15-01-20 20:09:48, David Hildenbrand wrote:
>> On 09.01.20 22:25, Scott Cheloha wrote:
>>> Searching for a particular memory block by id is an O(n) operation
>>> because each memory block's underlying device is kept in an unsorted
>>> linked list on the subsystem bus.
>>>
>>> We can cut the lookup cost to O(log n) if we cache the memory blocks in
>>> a radix tree. With a radix tree cache in place both memory subsystem
>>> initialization and memory hotplug run palpably faster on systems with a
>>> large number of memory blocks.
>>>
>>> Signed-off-by: Scott Cheloha <cheloha@linux.ibm.com>
>>> Acked-by: David Hildenbrand <david@redhat.com>
>>> Acked-by: Nathan Lynch <nathanl@linux.ibm.com>
>>> Acked-by: Michal Hocko <mhocko@suse.com>
>>
>> Soooo,
>>
>> I just learned that radix trees are nowadays only a wrapper for xarray
>> (for quite a while already!), and that the xarray interface shall be
>> used in new code.
>
> Good point. I somehow didn't realize this would add more work for a
> later code refactoring. The mapping should be pretty straightforward.

Yes it is. @Scott, care to send a fixup that does the mapping?

>
> Thanks for noticing!

Don noticed it, so thanks to him :)

--
Thanks,

David / dhildenb