On Fri, Feb 7, 2020 at 12:18 AM Martin KaFai Lau <kafai@xxxxxx> wrote:
>
> It was reported that the max_t, ilog2, and roundup_pow_of_two macros have
> exponential effects on the number of states in the sparse checker.
Patch looks good, but I'd like to point out that it's not just sparse.
You can see it with a simple
make net/core/bpf_sk_storage.i
grep 'smap->bucket_log = ' net/core/bpf_sk_storage.i | wc
and see the end result:
1 365071 2686974
That's one line (the assignment line) that is 2,686,974 characters in length.
Now, sparse does happen to react particularly badly to that (I didn't
look to why, but I suspect it's just that evaluating all the types
that don't actually ever end up getting used ends up being much more
expensive than it should be), but I bet it's not good for gcc either.
I do think this is a good test-case for sparse. Luc, have you looked
at what it is that then makes sparse use *so* much memory for this one
line?
Linus
