Date: Thu, 11 Sep 2025 15:20:23 +1200
From: Tao Liu <ltao@redhat.com>
Subject: [Crash-utility] [PATCH] bpf: Implement ringbuf_map memory
usage calculation
To: devel@lists.crash-utility.osci.io
Cc: Tao Liu <ltao@redhat.com>
Message-ID: <20250911032023.16833-1-ltao@redhat.com>
Content-Type: text/plain; charset="US-ASCII"; x-default=true
This patch replicates the kernel code for bpf ringbuf_map mm usage
calculation.
$ bpftool map create /sys/fs/bpf/rb0 type ringbuf key 0 value 0 entries $((1<<24)) name rb0
Before:
crash> bpf -m 12
ID BPF_MAP BPF_MAP_TYPE MAP_FLAGS
12 ffff8dc4d7c0ed00 RINGBUF 00000000
KEY_SIZE: 0 VALUE_SIZE: 0 MAX_ENTRIES: 16777216 MEMLOCK: (unknown)
NAME: "rb0" UID: (unused)
After:
crash> bpf -m 12
ID BPF_MAP BPF_MAP_TYPE MAP_FLAGS
12 ffff8dc4d7c0ed00 RINGBUF 00000000
KEY_SIZE: 0 VALUE_SIZE: 0 MAX_ENTRIES: 16777216 MEMLOCK: 16855320
NAME: "rb0" UID: (unused)
Thus, the output will be the same as bpftool:
$ bpftool map show id 12
12: ringbuf name rb0 flags 0x0
key 0B value 0B max_entries 16777216 memlock 16855320B
Signed-off-by: Tao Liu <ltao@redhat.com>
---
bpf.c | 30 +++++++++++++++++++++++++++++-
defs.h | 5 +++++
symbols.c | 5 +++++
3 files changed, 39 insertions(+), 1 deletion(-)
diff --git a/bpf.c b/bpf.c
index 466b244..43e4ff5 100644
--- a/bpf.c
+++ b/bpf.c
@@ -121,6 +121,26 @@ static ulong bpf_map_memory_size(int map_type, uint value_size,
return roundup((max_entries * size), PAGESIZE());
}
+/*
+ * Code replicated from kernel/bpf/ringbuf.c:ringbuf_map_mem_usage()
+*/
+static ulong ringbuf_map_mem_usage(struct bpf_info *bpf, int i)
+{
+ ulong nr_pages;
+ ulong usage = SIZE(bpf_ringbuf_map);
+ ulong rb = (ulong)(bpf->maplist[i].value) - OFFSET(bpf_ringbuf_map_map)
+ + OFFSET(bpf_ringbuf_map_rb);
+ readmem(rb, KVADDR, &rb, sizeof(ulong), "bpf_ringbuf *", RETURN_ON_ERROR);
It should be good to use the "FAULT_ON_ERROR" in readmem(), or you can check the returned error(if any) here. Both are fine to me.
+ readmem(rb + OFFSET(bpf_ringbuf_nr_pages), KVADDR, &nr_pages,
+ sizeof(ulong), "bpf_ringbuf.nr_pages", RETURN_ON_ERROR);
Ditto.
Other changes are good for me.
Thanks
Lianbo
+ usage += (nr_pages << PAGESHIFT());
+ ulong nr_meta_pages = (OFFSET(bpf_ringbuf_consumer_pos) >> PAGESHIFT()) + 2;
+ ulong nr_data_pages = UINT(bpf->bpf_map_buf + OFFSET(bpf_map_max_entries)) >> PAGESHIFT();
+ usage += (nr_meta_pages + 2 * nr_data_pages) * sizeof(void *);
+
+ return usage;
+}
+
void
cmd_bpf(void)
{
@@ -217,6 +237,7 @@ bpf_init(struct bpf_info *bpf)
STRUCT_SIZE_INIT(bpf_prog_aux, "bpf_prog_aux");
STRUCT_SIZE_INIT(bpf_map, "bpf_map");
STRUCT_SIZE_INIT(bpf_insn, "bpf_insn");
+ STRUCT_SIZE_INIT(bpf_ringbuf_map, "bpf_ringbuf_map");
MEMBER_OFFSET_INIT(bpf_prog_aux, "bpf_prog", "aux");
MEMBER_OFFSET_INIT(bpf_prog_type, "bpf_prog", "type");
MEMBER_OFFSET_INIT(bpf_prog_tag, "bpf_prog", "tag");
@@ -228,6 +249,10 @@ bpf_init(struct bpf_info *bpf)
MEMBER_OFFSET_INIT(bpf_map_map_flags, "bpf_map", "map_flags");
MEMBER_OFFSET_INIT(bpf_prog_aux_used_maps, "bpf_prog_aux", "used_maps");
MEMBER_OFFSET_INIT(bpf_prog_aux_used_map_cnt, "bpf_prog_aux", "used_map_cnt");
+ MEMBER_OFFSET_INIT(bpf_ringbuf_map_map, "bpf_ringbuf_map", "map");
+ MEMBER_OFFSET_INIT(bpf_ringbuf_map_rb, "bpf_ringbuf_map", "rb");
+ MEMBER_OFFSET_INIT(bpf_ringbuf_consumer_pos, "bpf_ringbuf", "consumer_pos");
+ MEMBER_OFFSET_INIT(bpf_ringbuf_nr_pages, "bpf_ringbuf", "nr_pages");
if (!VALID_STRUCT(bpf_prog) ||
!VALID_STRUCT(bpf_prog_aux) ||
!VALID_STRUCT(bpf_map) ||
@@ -664,7 +689,10 @@ do_map_only:
fprintf(fp, "%d\n", map_pages * PAGESIZE());
} else if ((msize = bpf_map_memory_size(type, value_size, key_size, max_entries)))
fprintf(fp, "%ld\n", msize);
- else
+#define BPF_MAP_TYPE_RINGBUF (0x1BUL)
+ else if (type == BPF_MAP_TYPE_RINGBUF) {
+ fprintf(fp, "%ld\n", ringbuf_map_mem_usage(bpf, i));
+ } else
fprintf(fp, "(unknown)");
fprintf(fp, " NAME: ");
diff --git a/defs.h b/defs.h
index 4fecb83..498c262 100644
--- a/defs.h
+++ b/defs.h
@@ -2274,6 +2274,10 @@ struct offset_table { /* stash of commonly-used offsets */
long request_queue_tag_set;
long blk_mq_tag_set_flags;
long blk_mq_tag_set_shared_tags;
+ long bpf_ringbuf_map_map;
+ long bpf_ringbuf_map_rb;
+ long bpf_ringbuf_consumer_pos;
+ long bpf_ringbuf_nr_pages;
};
struct size_table { /* stash of commonly-used sizes */
@@ -2452,6 +2456,7 @@ struct size_table { /* stash of commonly-used sizes */
long vmap_node;
long cpumask_t;
long task_struct_exit_state;
+ long bpf_ringbuf_map;
};
struct array_table {
diff --git a/symbols.c b/symbols.c
index ce0b441..19e1316 100644
--- a/symbols.c
+++ b/symbols.c
@@ -11868,6 +11868,10 @@ dump_offset_table(char *spec, ulong makestruct)
fprintf(fp, " thread_struct_gsbase: %ld\n", OFFSET(thread_struct_gsbase));
fprintf(fp, " thread_struct_fs: %ld\n", OFFSET(thread_struct_fs));
fprintf(fp, " thread_struct_gs: %ld\n", OFFSET(thread_struct_gs));
+ fprintf(fp, " bpf_ringbuf_map_map: %ld\n", OFFSET(bpf_ringbuf_map_map));
+ fprintf(fp, " bpf_ringbuf_map_rb: %ld\n", OFFSET(bpf_ringbuf_map_rb));
+ fprintf(fp, " bpf_ringbuf_consumer_pos: %ld\n", OFFSET(bpf_ringbuf_consumer_pos));
+ fprintf(fp, " bpf_ringbuf_nr_pages: %ld\n", OFFSET(bpf_ringbuf_nr_pages));
fprintf(fp, "\n size_table:\n");
fprintf(fp, " page: %ld\n", SIZE(page));
@@ -12148,6 +12152,7 @@ dump_offset_table(char *spec, ulong makestruct)
fprintf(fp, " percpu_counter: %ld\n", SIZE(percpu_counter));
fprintf(fp, " cpumask_t: %ld\n", SIZE(cpumask_t));
+ fprintf(fp, " bpf_ringbuf_map: %ld\n", SIZE(bpf_ringbuf_map));
fprintf(fp, "\n array_table:\n");
/*
--
2.47.0