bpf: ringbuf memory usage

A new helper ringbuf_map_mem_usage() is introduced to calculate ringbuf
memory usage.

The result as follows,
- before
15: ringbuf  name count_map  flags 0x0
        key 0B  value 0B  max_entries 65536  memlock 0B

- after
15: ringbuf  name count_map  flags 0x0
        key 0B  value 0B  max_entries 65536  memlock 78424B
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20230305124615.12358-8-laoar.shao@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/ringbuf.c

@@ -19,6 +19,7 @@
 	(offsetof(struct bpf_ringbuf, consumer_pos) >> PAGE_SHIFT)
 /* consumer page and producer page */
 #define RINGBUF_POS_PAGES 2
+#define RINGBUF_NR_META_PAGES (RINGBUF_PGOFF + RINGBUF_POS_PAGES)
 
 #define RINGBUF_MAX_RECORD_SZ (UINT_MAX/4)
 
@@ -96,7 +97,7 @@ static struct bpf_ringbuf *bpf_ringbuf_area_alloc(size_t data_sz, int numa_node)
 {
 	const gfp_t flags = GFP_KERNEL_ACCOUNT | __GFP_RETRY_MAYFAIL |
 			    __GFP_NOWARN | __GFP_ZERO;
-	int nr_meta_pages = RINGBUF_PGOFF + RINGBUF_POS_PAGES;
+	int nr_meta_pages = RINGBUF_NR_META_PAGES;
 	int nr_data_pages = data_sz >> PAGE_SHIFT;
 	int nr_pages = nr_meta_pages + nr_data_pages;
 	struct page **pages, *page;
@@ -336,6 +337,21 @@ static __poll_t ringbuf_map_poll_user(struct bpf_map *map, struct file *filp,
 	return 0;
 }
 
+static u64 ringbuf_map_mem_usage(const struct bpf_map *map)
+{
+	struct bpf_ringbuf *rb;
+	int nr_data_pages;
+	int nr_meta_pages;
+	u64 usage = sizeof(struct bpf_ringbuf_map);
+
+	rb = container_of(map, struct bpf_ringbuf_map, map)->rb;
+	usage += (u64)rb->nr_pages << PAGE_SHIFT;
+	nr_meta_pages = RINGBUF_NR_META_PAGES;
+	nr_data_pages = map->max_entries >> PAGE_SHIFT;
+	usage += (nr_meta_pages + 2 * nr_data_pages) * sizeof(struct page *);
+	return usage;
+}
+
 BTF_ID_LIST_SINGLE(ringbuf_map_btf_ids, struct, bpf_ringbuf_map)
 const struct bpf_map_ops ringbuf_map_ops = {
 	.map_meta_equal = bpf_map_meta_equal,
@@ -347,6 +363,7 @@ const struct bpf_map_ops ringbuf_map_ops = {
 	.map_update_elem = ringbuf_map_update_elem,
 	.map_delete_elem = ringbuf_map_delete_elem,
 	.map_get_next_key = ringbuf_map_get_next_key,
+	.map_mem_usage = ringbuf_map_mem_usage,
 	.map_btf_id = &ringbuf_map_btf_ids[0],
 };
 
@@ -361,6 +378,7 @@ const struct bpf_map_ops user_ringbuf_map_ops = {
 	.map_update_elem = ringbuf_map_update_elem,
 	.map_delete_elem = ringbuf_map_delete_elem,
 	.map_get_next_key = ringbuf_map_get_next_key,
+	.map_mem_usage = ringbuf_map_mem_usage,
 	.map_btf_id = &user_ringbuf_map_btf_ids[0],
 };