[Crash-utility] Re: [PATCH] bpf: Implement ringbuf_map memory usage calculation

Date: Thu, 11 Sep 2025 15:20:23 +1200 From: Tao Liu <ltao(a)redhat.com&gt; Subject: [Crash-utility] [PATCH] bpf: Implement ringbuf_map memory usage calculation To: devel(a)lists.crash-utility.osci.io Cc: Tao Liu <ltao(a)redhat.com&gt; Message-ID: <20250911032023.16833-1-ltao(a)redhat.com&gt; 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(a)redhat.com&gt; --- 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);

+ sizeof(ulong), "bpf_ringbuf.nr_pages", RETURN_ON_ERROR);

+ 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