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Date:   Thu, 16 Jan 2020 16:22:14 +0100
From:   Michal Hocko <mhocko@kernel.org>
To:     David Hildenbrand <david@redhat.com>
Cc:     Scott Cheloha <cheloha@linux.vnet.ibm.com>,
        linux-kernel@vger.kernel.org,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        nathanl@linux.ibm.com, ricklind@linux.vnet.ibm.com,
        Scott Cheloha <cheloha@linux.ibm.com>,
        Donald Dutile <ddutile@redhat.com>
Subject: Re: [PATCH v4] drivers/base/memory.c: cache blocks in radix tree to
 accelerate lookup
Message-ID: <20200116152214.GX19428@dhcp22.suse.cz>
References: <20191217193238-1-cheloha@linux.vnet.ibm.com>
 <20200109212516.17849-1-cheloha@linux.vnet.ibm.com>
 <181caae3-ffb8-c745-a4c9-1aef93ea6dd5@redhat.com>
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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.

Thanks for noticing!

-- 
Michal Hocko
SUSE Labs