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

On Mon, Sep 15, 2025 at 1:16 PM <devel-request(a)lists.crash-utility.osci.io&gt; wrote: > > 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); 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