Re: [PATCH] kmalloc_percpu

Rusty Russell (rusty@rustcorp.com.au)
Tue, 06 May 2003 14:08:27 +1000

In message <1052187119.983.5.camel@rth.ninka.net> you write:
> On Mon, 2003-05-05 at 18:52, Andrew Morton wrote:
> > Rusty Russell <rusty@rustcorp.com.au> wrote:
> > > OK. It has a size restriction: PERCPU_POOL_SIZE is the maximum total
> > > kmalloc_percpu + static DECLARE_PER_CPU you'll get, ever. This is the
> > > main downside. It's allocated at boot.
> >
> > And is subject to fragmentation.
> >
> > Is it not possible to go allocate another N * PERCPU_POOL_SIZE from
> > slab if it runs out?
>
> No, then you go back to things requireing multiple levels of
> dereferencing.

Actually, you can; my previous patch did this. But then all CPUS have
to be one continuous allocation: since modern big-SMP machines are
non-uniform, so you don't want this.

http://www.kernel.org/pub/linux/kernel/people/rusty/patches/Misc/kmalloc_percpu-orig.patch.gz

> I think the fixed size pool is perfectly reasonable.

Yes. It's a tradeoff. I think it's worth it at the moment (although
I'll add a limited printk to __alloc_percpu if it fails).

Cheers,
Rusty.

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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