Merge branch 'bpf: add percpu stats for bpf_map'

Anton Protopopov says:

====================
This series adds a mechanism for maps to populate per-cpu counters on
insertions/deletions. The sum of these counters can be accessed by a new kfunc
from map iterator and tracing programs.

The following patches are present in the series:

  * Patch 1 adds a generic per-cpu counter to struct bpf_map
  * Patch 2 adds a new kfunc to access the sum of per-cpu counters
  * Patch 3 utilizes this mechanism for hash-based maps
  * Patch 4 extends the preloaded map iterator to dump the sum
  * Patch 5 adds a self-test for the change

The reason for adding this functionality in our case (Cilium) is to get signals
about how full some heavy-used maps are and what the actual dynamic profile of
map capacity is. In the case of LRU maps this is impossible to get this
information anyhow else. The original presentation can be found here [1].

  [1] https://lpc.events/event/16/contributions/1368/

v4 -> v5:
* don't pass useless empty opts when creating a link, pass NULL (Hou)
* add a debug message (Hou)
* make code more readable (Alexei)
* remove the selftest which only checked that elem_count != NULL

v3 -> v4:
* fix selftests:
  * added test code for batch map operations
  * added a test for BPF_MAP_TYPE_HASH_OF_MAPS (Hou)
  * added tests for BPF_MAP_TYPE_LRU* with BPF_F_NO_COMMON_LRU (Hou)
  * map_info was called multiple times unnecessarily (Hou)
  * small fixes + some memory leaks (Hou)
* fixed wrong error path for freeing a non-prealloc map (Hou)
* fixed counters for batch delete operations (Hou)

v2 -> v3:
- split commits to better represent update logic (Alexei)
- remove filter from kfunc to allow all tracing programs (Alexei)
- extend selftests (Alexei)

v1 -> v2:
- make the counters generic part of struct bpf_map (Alexei)
- don't use map_info and /proc/self/fdinfo in favor of a kfunc (Alexei)
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 30 insertions, 0 deletions

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index f58895830ada..360433f14496 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -275,6 +275,7 @@ struct bpf_map {
 	} owner;
 	bool bypass_spec_v1;
 	bool frozen; /* write-once; write-protected by freeze_mutex */
+	s64 __percpu *elem_count;
 };
 
 static inline const char *btf_field_type_name(enum btf_field_type type)
@@ -2040,6 +2041,35 @@ bpf_map_alloc_percpu(const struct bpf_map *map, size_t size, size_t align,
 }
 #endif
 
+static inline int
+bpf_map_init_elem_count(struct bpf_map *map)
+{
+	size_t size = sizeof(*map->elem_count), align = size;
+	gfp_t flags = GFP_USER | __GFP_NOWARN;
+
+	map->elem_count = bpf_map_alloc_percpu(map, size, align, flags);
+	if (!map->elem_count)
+		return -ENOMEM;
+
+	return 0;
+}
+
+static inline void
+bpf_map_free_elem_count(struct bpf_map *map)
+{
+	free_percpu(map->elem_count);
+}
+
+static inline void bpf_map_inc_elem_count(struct bpf_map *map)
+{
+	this_cpu_inc(*map->elem_count);
+}
+
+static inline void bpf_map_dec_elem_count(struct bpf_map *map)
+{
+	this_cpu_dec(*map->elem_count);
+}
+
 extern int sysctl_unprivileged_bpf_disabled;
 
 static inline bool bpf_allow_ptr_leaks(void)