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

[Don Dutile]

On 1/16/20 10:28 AM, David Hildenbrand wrote:
> 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@xxxxxxxxxxxxx>
> > > > Acked-by: David Hildenbrand <david@xxxxxxxxxx>
> > > > Acked-by: Nathan Lynch <nathanl@xxxxxxxxxxxxx>
> > > > Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> > >
> > > 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 :)
Backporting XArray to RHEL-8, and continuing to support radix-tree api in RHEL-8 due to RHEL rulz, it wasn't stable/bug-free everyewhere, etc., was a challenge, thus my 'sensitivity' to seeing new radix-tree code upstream.

>