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

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Message-ID: <20200116152214.GX19428@dhcp22.suse.cz>
Date:   Thu, 16 Jan 2020 16:22:14 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Scott Cheloha <cheloha@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        nathanl@...ux.ibm.com, ricklind@...ux.vnet.ibm.com,
        Scott Cheloha <cheloha@...ux.ibm.com>,
        Donald Dutile <ddutile@...hat.com>
Subject: Re: [PATCH v4] drivers/base/memory.c: cache blocks in radix tree to
 accelerate lookup

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@...ux.ibm.com>
> > Acked-by: David Hildenbrand <david@...hat.com>
> > Acked-by: Nathan Lynch <nathanl@...ux.ibm.com>
> > Acked-by: Michal Hocko <mhocko@...e.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.

Thanks for noticing!

-- 
Michal Hocko
SUSE Labs