用crash工具学习Linux内核 —— 查看cgroup_roots

内核版本：5.14
ubuntu版本：20.04

参考：
Linux_schedule_cgroup.pdf

在开机时，会自动挂载cgroup文件系统，可以通过cat /proc/cgroups来查看当前在用的cgroup子系统。

root@ubuntu-vm:~# cat /proc/cgroups
#subsys_name    hierarchy       num_cgroups     enabled
cpuset             8                 1             1
cpu                7                 1             1
cpuacct            7                 1             1
blkio              6                 1             1
memory             4                 52            1
devices           12                 23            1
freezer           13                 1             1
perf_event        11                 1             1
hugetlb            3                 1             1
pids              10                 29            1
rdma               5                 1             1
misc               9                 1             1
debug              2                 1             1
root@ubuntu-vm:~# cat /proc/cgroups | wc -l
14

上面cpu和cpuacct的hierarchy是相同的，表示这两个子系统是一同挂载的，即：mount -t cgroup -o cpu,cpuacct，这里的log是通过proc_cgroupstats_show输出的:

**/* Display information about each subsystem and each hierarchy */
int proc_cgroupstats_show(struct seq_file *m, void *v)
{
	struct cgroup_subsys *ss;
	int i;

	seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n");
	/*
	 * ideally we don't want subsystems moving around while we do this.
	 * cgroup_mutex is also necessary to guarantee an atomic snapshot of
	 * subsys/hierarchy state.
	 */
	mutex_lock(&cgroup_mutex);

	for_each_subsys(ss, i)
		seq_printf(m, "%s\t%d\t%d\t%d\n",
			   ss->legacy_name, ss->root->hierarchy_id,
			   atomic_read(&ss->root->nr_cgrps),
			   cgroup_ssid_enabled(i));

	mutex_unlock(&cgroup_mutex);
	return 0;
}

当mount -t cgroup -o memory,xxx时，如果memory子系统还没有cgroup_root的话，会创建新的cgroup_root结构，并将其加入到全局cgroup_roots链表中，下面用crash工具的list命令
来遍历这个链表，输出每个cgroup_root的信息。

• 获取cgroup_roots的地址

crash> sym cgroup_roots
ffffffffb7f509a0 (D) cgroup_roots

• 遍历1

crash> list -o cgroup_root.root_list  -H ffffffffb7f509a0 | wc -l
14
crash> list -o cgroup_root.root_list  -H ffffffffb7f509a0
ffffa3b7802cc000
ffffa3b7802ca000
ffffa3b7802c8000
ffffa3b782b8e000
ffffa3b782b8c000
ffffa3b782b8a000
ffffa3b782b88000
ffffa3b780bf6000
ffffa3b780bf4000
ffffa3b780bf2000
ffffa3b780bf0000
ffffa3b781696000
ffffa3b781694000
ffffffffb7f509c0

• 查看具体每个cgroup_root的hierarchy：

crash> list -o cgroup_root.root_list -s cgroup_root.hierarchy_id -H ffffffffb7f509a0 -r
ffffffffb7f509c0
  hierarchy_id = 0,  # 默认cgroup_root
ffffa3b781694000
  hierarchy_id = 1,
ffffa3b781696000
  hierarchy_id = 2,
ffffa3b780bf0000
  hierarchy_id = 3,
ffffa3b780bf2000
  hierarchy_id = 4,
ffffa3b780bf4000
  hierarchy_id = 5,
ffffa3b780bf6000
  hierarchy_id = 6,
ffffa3b782b88000
  hierarchy_id = 7,
ffffa3b782b8a000
  hierarchy_id = 8,
ffffa3b782b8c000
  hierarchy_id = 9,
ffffa3b782b8e000
  hierarchy_id = 10,
ffffa3b7802c8000
  hierarchy_id = 11,
ffffa3b7802ca000
  hierarchy_id = 12,
ffffa3b7802cc000
  hierarchy_id = 13,

• 查看具体每个cgroup_root的更多信息：

crash> list -o cgroup_root.root_list -s cgroup_root.hierarchy_id,subsys_mask,nr_cgrps -H ffffffffb7f509a0 -rx
ffffffffb7f509c0
  hierarchy_id = 0x0,
  subsys_mask = 0x0,
  nr_cgrps = {
    counter = 0x1f
  },
ffffa3b781694000
  hierarchy_id = 0x1,
  subsys_mask = 0x0,
  nr_cgrps = {
    counter = 0x1f
  },
ffffa3b781696000
  hierarchy_id = 0x2,
  subsys_mask = 0x1000,
  nr_cgrps = {
    counter = 0x1
  },
ffffa3b780bf0000
  hierarchy_id = 0x3,
  subsys_mask = 0x100,
  nr_cgrps = {
    counter = 0x1
  },
ffffa3b780bf2000
  hierarchy_id = 0x4,
  subsys_mask = 0x10,
  nr_cgrps = {
    counter = 0x34
  },
ffffa3b780bf4000
  hierarchy_id = 0x5,
  subsys_mask = 0x400,
  nr_cgrps = {
    counter = 0x1
  },
ffffa3b780bf6000
  hierarchy_id = 0x6,
  subsys_mask = 0x8,
  nr_cgrps = {
    counter = 0x1
  },
ffffa3b782b88000
  hierarchy_id = 0x7,
  subsys_mask = 0x6,
  nr_cgrps = {
    counter = 0x1
  },
ffffa3b782b8a000
  hierarchy_id = 0x8,
  subsys_mask = 0x1,
  nr_cgrps = {
    counter = 0x1
  },
ffffa3b782b8c000
  hierarchy_id = 0x9,
  subsys_mask = 0x800,
  nr_cgrps = {
    counter = 0x1
  },
ffffa3b782b8e000
  hierarchy_id = 0xa,
  subsys_mask = 0x200,
  nr_cgrps = {
    counter = 0x1d
  },
ffffa3b7802c8000
  hierarchy_id = 0xb,
  subsys_mask = 0x80,
  nr_cgrps = {
    counter = 0x1
  },
ffffa3b7802ca000
  hierarchy_id = 0xc,
  subsys_mask = 0x20,
  nr_cgrps = {
    counter = 0x17
  },
ffffa3b7802cc000
  hierarchy_id = 0xd,
  subsys_mask = 0x40,
  nr_cgrps = {
    counter = 0x1
  },

完。