Re: [PATCH bpf-next] bpf: cap BPF_PROG_PACK_SIZE to 2MB * num_possible_nodes()

[Alexei Starovoitov]

On Fri, Mar 8, 2024 at 8:55 AM Song Liu <song@xxxxxxxxxx> wrote:
>
> On Fri, Mar 8, 2024 at 4:07 AM Puranjay Mohan <puranjay12@xxxxxxxxx> wrote:
> >
> > On some architectures like ARM64, PMD_SIZE can be really large in some
> > configurations. Like with CONFIG_ARM64_64K_PAGES=y the PMD_SIZE is
> > 512MB.
> >
> > Use 2MB * num_possible_nodes() as the upper limit for allocations done
> > through the prog pack allocator.
> >
> > Fixes: ea2babac63d4 ("bpf: Simplify bpf_prog_pack_[size|mask]")
> > Reported-by: "kernelci.org bot" <bot@xxxxxxxxxxxx>
> > Closes: https://lore.kernel.org/all/7e216c88-77ee-47b8-becc-a0f780868d3c@xxxxxxxxxxxxx/
> > Suggested-by: Song Liu <song@xxxxxxxxxx>
> > Signed-off-by: Puranjay Mohan <puranjay12@xxxxxxxxx>
> > ---
> >  kernel/bpf/core.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> > index 134b7979f537..83a3b6964e54 100644
> > --- a/kernel/bpf/core.c
> > +++ b/kernel/bpf/core.c
> > @@ -893,8 +893,17 @@ static LIST_HEAD(pack_list);
> >   * CONFIG_MMU=n. Use PAGE_SIZE in these cases.
> >   */
> >  #ifdef PMD_SIZE
> > +/*
> > + * PMD_SIZE is really big for some archs. It doesn't make sense to
> > + * reserve too much memory in one allocation. Cap BPF_PROG_PACK_SIZE to
> > + * 2MiB * num_possible_nodes().
> > + */
>
> In BPF code, we prefer a different style of multiple line comments:
>
> /* PMD_SIZE is really big for some archs. It doesn't make sense to
>  * reserve too much memory in one allocation. Cap BPF_PROG_PACK_SIZE to
>  * 2MiB * num_possible_nodes().
>  */

Fixed up while applying. Thanks everyone.