Re: [PATCH] kallsyms: cache bpf symbols to avoid quadratic iteration

[Ivan Babrou]

On Thu, Feb 5, 2026 at 3:11 PM Alexei Starovoitov
<alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Thu, Jan 29, 2026 at 8:50 PM Ivan Babrou via B4 Relay
> <devnull+ivan.cloudflare.com@xxxxxxxxxx> wrote:
> >
> > From: Ivan Babrou <ivan@xxxxxxxxxxxxxx>
> >
> > The existing code iterates the whole list of bpf ksyms until the right
> > one is found, which means quadratic complexity on top of linked list
> > pointer chasing under rcu. This is't noticeable for most installations,
> > but when one has 10000 bpf programs loaded, things start to add up and
> > reading from `/proc/kallsyms` slows down a lot.
>
> How real is this? 10k bpf programs?

Very much real.

> >  static int get_ksymbol_bpf(struct kallsym_iter *iter)
> >  {
> > +       unsigned int index = iter->pos - iter->pos_ftrace_mod_end;
> >         int ret;
> >
> > +       if (iter->bpf_cache) {
> > +               if (index >= iter->bpf_cache_count) {
> > +                       iter->pos_bpf_end = iter->pos;
> > +                       return 0;
> > +               }
> > +
> > +               strscpy(iter->module_name, "bpf", MODULE_NAME_LEN);
> > +               iter->exported = 0;
> > +               strscpy(iter->name, iter->bpf_cache[index].name, KSYM_NAME_LEN);
> > +               iter->value = iter->bpf_cache[index].value;
> > +               iter->type = BPF_SYM_ELF_TYPE;
> > +
> > +               return 1;
> > +       }
>
> I'm sure there are other ways to speed up get_ksymbol_bpf().
> bpf_kallsyms is a list, but the same symbols are also in
> struct latch_tree_root bpf_tree
> Integrate it into get_ksymbol_bpf().
> latch_tree_find() will be surely faster than linear search in the list.
> Or go the extra mile and implement an iterator for latch_tree.

How do you feel about Florian's (cc'd) patch here?

* https://gist.github.com/florianl/41e2bce29ffde797536eef9b2e47ba92

I can take a stab at using bpf_tree like you suggested, but if you
like his patch, we can just go with that.

>
> pw-bot: cr