On Mon, Aug 07, 2023 at 11:11:04PM +0200, Thomas Gleixner wrote:
> On Mon, Aug 07 2023 at 14:18, Peter Zijlstra wrote:
> > /**
> > * futex_hash - Return the hash bucket in the global hash
> > * @key: Pointer to the futex key for which the hash is calculated
> > @@ -114,10 +137,29 @@ late_initcall(fail_futex_debugfs);
> > */
> > struct futex_hash_bucket *futex_hash(union futex_key *key)
> > {
> > - u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
> > + u32 hash = jhash2((u32 *)key,
> > + offsetof(typeof(*key), both.offset) / sizeof(u32),
> > key->both.offset);
> > + int node = key->both.node;
> > +
> > + if (node == -1) {
>
> NUMA_NO_NODE please all over the place.
Ah, so our (futex2) ABI states this needs to be -1, but in theory
someone could come along and change the kernel internal NUMA_NO_NODE to
something else.
That is, I explicitly chose not to use it. I can of course, because as
of now these values do match.
> > + /*
> > + * In case of !FLAGS_NUMA, use some unused hash bits to pick a
> > + * node -- this ensures regular futexes are interleaved across
> > + * the nodes and avoids having to allocate multiple
> > + * hash-tables.
> > + *
> > + * NOTE: this isn't perfectly uniform, but it is fast and
> > + * handles sparse node masks.
> > + */
> > + node = (hash >> futex_hashshift) % nr_node_ids;
> > + if (!node_possible(node)) {
> > + node = find_next_bit_wrap(node_possible_map.bits,
> > + nr_node_ids, node);
> > + }
>
> Smart.
Thanks :-)
> >
> > +static inline unsigned int futex_size(unsigned int flags)
> > +{
> > + return 1 << (flags & FLAGS_SIZE_MASK);
> > +}
> > +
> > static inline bool futex_flags_valid(unsigned int flags)
>
> If you reorder these two functions in the patch which introduces them,
> this diff gets readable :)
Durr, I knew I was forgetting something, will do.
