Messages in this thread | | | From | David Hildenbrand <> | Subject | Re: [PATCH v4] drivers/base/memory.c: cache blocks in radix tree to accelerate lookup | Date | Thu, 9 Jan 2020 23:35:28 +0100 |
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> Am 09.01.2020 um 23:28 schrieb Andrew Morton <akpm@linux-foundation.org>: > > On Thu, 9 Jan 2020 23:17:09 +0100 David Hildenbrand <david@redhat.com> wrote: > >> >> >>>> Am 09.01.2020 um 23:00 schrieb Andrew Morton <akpm@linux-foundation.org>: >>> >>> On Thu, 9 Jan 2020 15:25:16 -0600 Scott Cheloha <cheloha@linux.vnet.ibm.com> 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. >>>> >>>> ... >>>> >>>> @@ -56,6 +57,13 @@ static struct bus_type memory_subsys = { >>>> .offline = memory_subsys_offline, >>>> }; >>>> >>>> +/* >>>> + * Memory blocks are cached in a local radix tree to avoid >>>> + * a costly linear search for the corresponding device on >>>> + * the subsystem bus. >>>> + */ >>>> +static RADIX_TREE(memory_blocks, GFP_KERNEL); >>> >>> What protects this tree from racy accesses? >> >> I think the device hotplug lock currently (except during boot where no races can happen). >> > > So this? > > --- a/drivers/base/memory.c~drivers-base-memoryc-cache-blocks-in-radix-tree-to-accelerate-lookup-fix > +++ a/drivers/base/memory.c > @@ -61,6 +61,9 @@ static struct bus_type memory_subsys = { > * Memory blocks are cached in a local radix tree to avoid > * a costly linear search for the corresponding device on > * the subsystem bus. > + * > + * Protected by mem_hotplug_lock in mem_hotplug_begin(), and by the guaranteed > + * single-threadness at boot time. > */ > static RADIX_TREE(memory_blocks, GFP_KERNEL); > > > But are we sure this is all true?
I think the device hotplug lock, not the memory hotplug lock. Will double check later. >
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