On Fri, Jul 3, 2009 at 9:50 AM, Andrew Morton<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I think you're saying "for each pid N in the cgroup, set the Nth
> element in an IDR tree".
Right.
> That would work. And it automatically gives
> ordered traversal and dupe removal.
>
> I don't think IDRs permit in-order traversal, whereas radix-trees do
> support this.
I thought that an IDR *was* a form of radix tree.
Looking at the IDR API it doesn't appear support the notion of "insert
an entry with id N" anyway.
> Unfortunately radix-trees are presented as operating on
> void* data, so one would need to do some typecasting when storing
> BITS_PER_LONG-sized bitfields inside them.
That would mean adding something a bit like the IDA wrapper that
converts IDR to deal with bitfields?
Is the benefit of avoiding a vmalloc() at all costs really worth the
additional complexity, versus just doing:
if (size > 2 * PAGE_SIZE) {
array = vmalloc(size);
} else {
array = kmalloc(size, GFP_KERNEL);
}
?
That would only require vmalloc on cgroups with >2048 tasks, which is
going to be pretty rare, and is way simpler.
Paul
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