On Tue, Jul 12, 2022 at 1:53 AM Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > On Mon, Jul 11, 2022 at 04:35:19PM -0700, Hao Luo wrote: > > Hi Hao Xiang, > > > > On Mon, Jul 11, 2022 at 3:50 PM Hao Xiang . <hao.xiang@xxxxxxxxxxxxx> wrote: > > > > > > Ping... > > > > > > Can someone please help to shed some light on this? > > > > > > Thanks, Hao > > > > > > On Sun, Jul 3, 2022 at 3:33 PM Hao Xiang . <hao.xiang@xxxxxxxxxxxxx> wrote: > > > > > > > > Hi everyone, > > > > > > > > I am super new to bpf and the open source community in general. Please > > > > bear with me asking some basic questions. > > > > We are working on a bpf monitoring tool to track the CPU and memory > > > > usage for all bpf programs loaded in the system. We were able to get > > > > CPU usage per bpf program with the BPF_OBJ_GET_INFO_BY_ID syscall on a > > > > bpf prog object. We are trying to do the same on a map object to query > > > > for per map memory usage. The information returned from bpf_map_info > > > > only contains things like max_entries, key_size, value_size, which can > > > > be used to calculate estimated memory allocation size. But we are also > > > > interested in knowing how much memory is actually being used by our > > > > program. For instance, one of our bpf program uses a map with type > > > > hashtable. The hashtable is created with a chunk of pre-allocated > > > > memory based on the max_entres, key_size and value size. The > > > > pre-allocated size is useful information to know but so is the current > > > > number of entries in the hashtable. We used to run into a performance > > > > issue where our bpf map's max_entries is set to be too small and we > > > > end up totally exhausting the pre-allocated memory. So knowing things > > > > like current entry count VS max entry count of a hashtable is useful > > > > information for us. > > > > With that being said, we have a few questions and hopefully we can get > > > > some help from the community. > > > > 1) We couldn't find anything in bpf_map_info to give us the current > > > > entry count of a hashtable. I read that bpf_map_info returns > > > > information about a map object in general. So it makes total sense to > > > > not have information of a particular map type. But is there an > > > > existing place we can get the per map type information (eg, the > > > > current entry count of a hashtable, the number of elements pushed to a > > > > stack, etc)? > > > > cc more BPF experts for their comments. > > > > I agree with you that knowing the current space usage of a map is > > quite helpful. In my understanding, a naive and inefficient way to > > estimate space usage is iterating the map and counting the map > > elements. That's doable, but may not be the best method though. > > Regarding auto-adjusting map size, I remember Andrii talked about > > resizable hash maps, maybe he can tell you more [1]. > > we keep entries count for hash map, maybe we could just add > 'current count' to bpf_map_info, it seems generic enough We actually don't keep a count for the default case of prealloc.
