perf_mem__lvl_scnprintf
n += perf_mem__lvl_scnprintf(out + n, sizeof out - n, mi);
i += perf_mem__lvl_scnprintf(out + i, sz, mem_info);
int perf_mem__lvl_scnprintf(char *out, size_t sz, const struct mem_info *mem_info);
perf_mem__lvl_scnprintf(out, sizeof(out), he->mem_info);