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

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Message-ID: <181caae3-ffb8-c745-a4c9-1aef93ea6dd5@redhat.com>
Date:   Wed, 15 Jan 2020 20:09:48 +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>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     nathanl@...ux.ibm.com, ricklind@...ux.vnet.ibm.com,
        mhocko@...e.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 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.

include/linux/radix-tree.h:

/* Keep unconverted code working */
#define radix_tree_root		xarray
[...]

Do we want to convert this code before sending it to Linus'? (resend
this patch, or a fixup on top)

-- 
Thanks,

David / dhildenb