linux-kernel - Re: [PATCH v3] drivers/base/memory.c: cache blocks in radix tree to accelerate lookup

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Date:   Wed, 18 Dec 2019 10:00:49 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Scott Cheloha <cheloha@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     nathanl@...ux.ibm.com, ricklind@...ux.vnet.ibm.com
Subject: Re: [PATCH v3] drivers/base/memory.c: cache blocks in radix tree to
 accelerate lookup

On 17.12.19 20:32, Scott Cheloha wrote:
> Searching for a particular memory block by id is slow because each block
> device is kept in an unsorted linked list on the subsystem bus.
> 
> Lookup is much faster if we cache the blocks in a radix tree.  Memory
> subsystem initialization and hotplug/hotunplug is at least a little faster
> for any machine with more than ~100 blocks, and the speedup grows with
> the block count.
> 
> Signed-off-by: Scott Cheloha <cheloha@...ux.vnet.ibm.com>
> Acked-by: David Hildenbrand <david@...hat.com>
> ---
> v2 incorporates suggestions from David Hildenbrand.
> 
> v3 changes:
>   - Rebase atop "drivers/base/memory.c: drop the mem_sysfs_mutex"
> 
>   - Be conservative: don't use radix_tree_for_each_slot() in
>     walk_memory_blocks() yet.  It introduces RCU which could
>     change behavior.  Walking the tree "by hand" with
>     find_memory_block_by_id() is slower but keeps the patch
>     simple.

Fine with me (splitting it out, e.g., into an addon patch), however, as
readers/writers run mutually exclusive, there is nothing to worry about
here. RCU will not make a difference.

Thanks!

-- 
Thanks,

David / dhildenb