Re: [bpf-next:master 5/7] kernel/bpf/core.c:900:5: warning: '__pte_index_size' is not defined, evaluates to 0

[Puranjay Mohan <puranjay12@xxxxxxxxx>]

Hi Alexei,

On Sat, Mar 9, 2024 at 5:38 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> Puranjay,
>
> Looks like I have to drop this patch for now,
> since PMD_SIZE is not a constant on all archs
> that can be evaluated by a preprocessor.
>
> We need to find a different way.
>

How about we define it like:
-#define BPF_PROG_PACK_SIZE (PMD_SIZE * num_possible_nodes())
+/*
+ * 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().
+ */
+#define BPF_PROG_PACK_SIZE ((PMD_SIZE <= (1 << 21)) ? (PMD_SIZE *
num_possible_nodes())  \
+
                             : ((1 << 21) * num_possible_nodes()))

So, it will be computed at runtime. This adds more performance
overhead but this is called very infrequently
so shouldn't matter.

Or we can hardcode it as `2MB * num_possible_nodes()` because
PMD size in most architectures will be 2MB or larger but never smaller.

Thanks,
Puranjay