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Subject: Re: [PATCH v4] drivers/base/memory.c: cache blocks in radix tree to
 accelerate lookup
To:     Michal Hocko <mhocko@kernel.org>
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>
References: <20191217193238-1-cheloha@linux.vnet.ibm.com>
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From:   David Hildenbrand <david@redhat.com>
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Message-ID: <765a07fe-47e9-fe3d-716a-44d9ee4a5e99@redhat.com>
Date:   Thu, 16 Jan 2020 16:28:10 +0100
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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