bpf: Add percpu LRU list

Instead of having a common LRU list, this patch allows a
percpu LRU list which can be selected by specifying a map
attribute.  The map attribute will be added in the later
patch.

While the common use case for LRU is #reads >> #updates,
percpu LRU list allows bpf prog to absorb unusual #updates
under pathological case (e.g. external traffic facing machine which
could be under attack).

Each percpu LRU is isolated from each other.  The LRU nodes (including
free nodes) cannot be moved across different LRU Lists.

Here are the update performance comparison between
common LRU list and percpu LRU list (the test code is
at the last patch):

[root@kerneltest003.31.prn1 ~]# for i in 1 4 8; do echo -n "$i cpus: "; \
./map_perf_test 16 $i | awk '{r += $3}END{print r " updates"}'; done
 1 cpus: 2934082 updates
 4 cpus: 7391434 updates
 8 cpus: 6500576 updates

[root@kerneltest003.31.prn1 ~]# for i in 1 4 8; do echo -n "$i cpus: "; \
./map_perf_test 32 $i | awk '{r += $3}END{printr " updates"}'; done
  1 cpus: 2896553 updates
  4 cpus: 9766395 updates
  8 cpus: 17460553 updates

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 2 deletions

diff --git a/kernel/bpf/bpf_lru_list.h b/kernel/bpf/bpf_lru_list.h
index aaa2445ed1ca..5c35a98d02bf 100644
--- a/kernel/bpf/bpf_lru_list.h
+++ b/kernel/bpf/bpf_lru_list.h
@@ -53,11 +53,15 @@ struct bpf_common_lru {
 typedef bool (*del_from_htab_func)(void *arg, struct bpf_lru_node *node);
 
 struct bpf_lru {
-	struct bpf_common_lru common_lru;
+	union {
+		struct bpf_common_lru common_lru;
+		struct bpf_lru_list __percpu *percpu_lru;
+	};
 	del_from_htab_func del_from_htab;
 	void *del_arg;
 	unsigned int hash_offset;
 	unsigned int nr_scans;
+	bool percpu;
 };
 
 static inline void bpf_lru_node_set_ref(struct bpf_lru_node *node)
@@ -68,7 +72,7 @@ static inline void bpf_lru_node_set_ref(struct bpf_lru_node *node)
 	node->ref = 1;
 }
 
-int bpf_lru_init(struct bpf_lru *lru, u32 hash_offset,
+int bpf_lru_init(struct bpf_lru *lru, bool percpu, u32 hash_offset,
 		 del_from_htab_func del_from_htab, void *delete_arg);
 void bpf_lru_populate(struct bpf_lru *lru, void *buf, u32 node_offset,
 		      u32 elem_size, u32 nr_elems);