Re: [PATCH v2 11/14] futex: Implement FUTEX2_NUMA
From: Thomas Gleixner <hidden>
Date: 2023-08-07 21:11:11
Also in:
linux-arch, linux-mm, lkml
On Mon, Aug 07 2023 at 14:18, Peter Zijlstra wrote:
quoted hunk ↗ jump to hunk
/** * 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.
+ /*
+ * 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.
+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 :) Aside of that this thing is really hard to review :)