> On 9. Jan 2025, at 18:37, Anton Protopopov <aspsk@xxxxxxxxxxxxx> wrote: > > On 25/01/07 12:10PM, Charalampos Stylianopoulos wrote: >> (sorry for double posting, this time in plain text) >> Thanks a lot for the feedback! >> >> So, to double check, the suggestion is to only extend the libbpf API >> with a new helper that does pretty much what get_cur_elements() does >> in tools/testing/selftests/bpf/map_tests/map_percpu_stats.c ? > > What is your use case for getting the number of elements in a > particular map? Will it work for you to just use a variant of > get_cur_elements() from selftests vs. adding new API to libbpf? (On behalf of Charalampos Stylianopoulos) we would like to get the number of elements in some maps for monitoring purposes. The end goal is to get someone paged when a fixed-capacity map is about to start rejecting inserts. We aim to operate a large number of apps in containers (custom packet processing services, telekom). We find it most convenient for an app itself to expose metrics concerning the maps it has created. We currently use a map iterator and a bunch of bpf_probe_read_kernel. We foresee the number of maps in our systems getting significantly higher in the near future. Therefore enumerating every map in the system to get a number of elements in a particular map doesn't look sustainable. How do you feel about introducing bpf_map_sum_elem_count_by_fd kfunc, available in syscall programs? > > [Also, please try not to top-post, see https://www.idallen.com/topposting.html] > >>> On Tue, 7 Jan 2025 at 08:44, Anton Protopopov <aspsk@xxxxxxxxxxxxx> wrote: >>>> >>>> On 25/01/06 05:19PM, Daniel Borkmann wrote: >>>>> On 1/6/25 3:53 PM, Charalampos Stylianopoulos wrote: >>>>>> This patch series provides an easy way for userspace applications to >>>>>> query the number of entries currently present in a map. >>>>>> >>>>>> Currently, the number of entries in a map is accessible only from kernel space >>>>>> and eBPF programs. A userspace program that wants to track map utilization has to >>>>>> create and attach an eBPF program solely for that purpose. >>>>>> >>>>>> This series makes the number of entries in a map easily accessible, by extending the >>>>>> main bpf syscall with a new command. The command supports only maps that already >>>>>> track utilization, namely hash maps, LPM maps and queue/stack maps. >>>>> >>>>> An earlier attempt to directly expose it to user space can be found here [0], which >>>>> eventually led to [1] to only expose it via kfunc for BPF programs in order to avoid >>>>> extending UAPI. >>>>> >>>>> Perhaps instead add a small libbpf helper (e.g. bpf_map__current_entries to complement >>>>> bpf_map__max_entries) which does all the work to extract that info via [1] underneath? >>>> >>>> One small thingy here is that bpf_map_sum_elem_count() is only >>>> available from the map iterator. Which means that to get the >>>> bpf_map_sum_elem_count() for one map only, one have to iterate >>>> through the whole set of maps (and filter out all but one). >>>> >>>> I wanted to follow up my series by either adding the result of >>>> calling bpf_map_sum_elem_count() to map_info as u32 or to add >>>> possibility to provide a map_fd/map_id when creating an iterator >>>> (so that it is only called for one map). But so far I haven't >>>> a real use case for getting the number of elements for one map only. >>>> >>>>> Thanks, >>>>> Daniel >>>>> >>>>> [0] https://lore.kernel.org/bpf/20230531110511.64612-1-aspsk@xxxxxxxxxxxxx/ >>>>> [1] https://lore.kernel.org/bpf/20230705160139.19967-1-aspsk@xxxxxxxxxxxxx/ >>>>> https://lore.kernel.org/bpf/20230719092952.41202-1-aspsk@xxxxxxxxxxxxx/ >>>>> >>>>>> Charalampos Stylianopoulos (4): >>>>>> bpf: Add map_num_entries map op >>>>>> bpf: Add bpf command to get number of map entries >>>>>> libbpf: Add support for MAP_GET_NUM_ENTRIES command >>>>>> selftests/bpf: Add tests for bpf_map_get_num_entries >>>>>> >>>>>> include/linux/bpf.h | 3 ++ >>>>>> include/linux/bpf_local_storage.h | 1 + >>>>>> include/uapi/linux/bpf.h | 17 +++++++++ >>>>>> kernel/bpf/devmap.c | 14 ++++++++ >>>>>> kernel/bpf/hashtab.c | 10 ++++++ >>>>>> kernel/bpf/lpm_trie.c | 8 +++++ >>>>>> kernel/bpf/queue_stack_maps.c | 11 +++++- >>>>>> kernel/bpf/syscall.c | 32 +++++++++++++++++ >>>>>> tools/include/uapi/linux/bpf.h | 17 +++++++++ >>>>>> tools/lib/bpf/bpf.c | 16 +++++++++ >>>>>> tools/lib/bpf/bpf.h | 2 ++ >>>>>> tools/lib/bpf/libbpf.map | 1 + >>>>>> .../bpf/map_tests/lpm_trie_map_basic_ops.c | 5 +++ >>>>>> tools/testing/selftests/bpf/test_maps.c | 35 +++++++++++++++++++ >>>>>> 14 files changed, 171 insertions(+), 1 deletion(-) >>>>>> >>>>>
