Re: [Patch 1/2] CPU hotplug compatible alloc_percpu

[Martin Peschke <mp3@de.ibm.com>]

Andrew Morton wrote:
> On Mon, 24 Jul 2006 19:16:54 +0200
> Martin Peschke <mp3@de.ibm.com> wrote:
>
> > This patch splits alloc_percpu() up into two phases. Likewise for
> > free_percpu(). This allows clients to limit initial allocations to
> > online cpu's, and to populate or depopulate per-cpu data at run time as
> > needed:
> >
> >   struct my_struct *obj;
> >
> >   /* initial allocation for online cpu's */
> >   obj = percpu_alloc(sizeof(struct my_struct), GFP_KERNEL);
> >
> >   ...
> >
> >   /* populate per-cpu data for cpu coming online */
> >   ptr = percpu_populate(obj, sizeof(struct my_struct), GFP_KERNEL, cpu);
> >
> >   ...
> >
> >   /* access per-cpu object */
> >   ptr = percpu_ptr(obj, smp_processor_id());
> >
> >   ...
> >
> >   /* depopulate per-cpu data for cpu going offline */
> >   percpu_depopulate(obj, cpu);
> >
> >   ...
> >
> >   /* final removal */
> >   percpu_free(obj);
>
> That looks pretty thorough.
>
> The one little nit I'd have is that the code passes cpumasks by value.  See
> the tricks in <linux/cpumask.h> which pretend to take the caller's cpumask
> by value but which instead pass it via const reference to the callee.
>
> CONFIG_NR_CPUS=1024 leads to a 128-byte cpumask_t.  It's worth doing.

Oops. I will send a patch.

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