Re: [PATCH bpf-next v2 2/7] mm/percpu.c: introduce pcpu_alloc_size()

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Thu, Oct 19, 2023 at 9:09 PM Dennis Zhou <dennis@kernel.org> wrote:
>
> On Wed, Oct 18, 2023 at 07:33:38PM +0800, Hou Tao wrote:
> > From: Hou Tao <houtao1@huawei.com>
> >
> > Introduce pcpu_alloc_size() to get the size of the dynamic per-cpu
> > area. It will be used by bpf memory allocator in the following patches.
> > BPF memory allocator maintains per-cpu area caches for multiple area
> > sizes and its free API only has the to-be-freed per-cpu pointer, so it
> > needs the size of dynamic per-cpu area to select the corresponding cache
> > when bpf program frees the dynamic per-cpu pointer.
> >
> > Signed-off-by: Hou Tao <houtao1@huawei.com>
> > ---
> >  include/linux/percpu.h |  1 +
> >  mm/percpu.c            | 30 ++++++++++++++++++++++++++++++
> >  2 files changed, 31 insertions(+)
> >
> > diff --git a/include/linux/percpu.h b/include/linux/percpu.h
> > index 68fac2e7cbe6..8c677f185901 100644
> > --- a/include/linux/percpu.h
> > +++ b/include/linux/percpu.h
> > @@ -132,6 +132,7 @@ extern void __init setup_per_cpu_areas(void);
> >  extern void __percpu *__alloc_percpu_gfp(size_t size, size_t align, gfp_t gfp) __alloc_size(1);
> >  extern void __percpu *__alloc_percpu(size_t size, size_t align) __alloc_size(1);
> >  extern void free_percpu(void __percpu *__pdata);
> > +extern size_t pcpu_alloc_size(void __percpu *__pdata);
> >
> >  DEFINE_FREE(free_percpu, void __percpu *, free_percpu(_T))
> >
> > diff --git a/mm/percpu.c b/mm/percpu.c
> > index 76b9c5e63c56..b0cea2dc16a9 100644
> > --- a/mm/percpu.c
> > +++ b/mm/percpu.c
> > @@ -2244,6 +2244,36 @@ static void pcpu_balance_workfn(struct work_struct *work)
> >       mutex_unlock(&pcpu_alloc_mutex);
> >  }
> >
> > +/**
> > + * pcpu_alloc_size - the size of the dynamic percpu area
> > + * @ptr: pointer to the dynamic percpu area
> > + *
> > + * Return the size of the dynamic percpu area @ptr.
> > + *
>
> Alexei, can you modify the above comment to:
>
> Returns the size of the @ptr allocation.  This is undefined for statically
> defined percpu variables as there is no corresponding chunk->bound_map.

Good point! Will do.

Thanks for the quick review!