kernel/sched/psi.c: expose pressure metrics on root cgroup

Pressure metrics are already recorded and exposed in procfs for the
entire system, but any tool which monitors cgroup pressure has to
special case the root cgroup to read from procfs.  This patch exposes
the already recorded pressure metrics on the root cgroup.

Link: http://lkml.kernel.org/r/20190510174938.3361741-1-dschatzberg@fb.com
Signed-off-by: Dan Schatzberg <dschatzberg@fb.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 14 insertions, 7 deletions

diff --git a/include/linux/psi.h b/include/linux/psi.h
index af892c290116..7b3de7321219 100644
--- a/include/linux/psi.h
+++ b/include/linux/psi.h
@@ -12,6 +12,7 @@ struct css_set;
 #ifdef CONFIG_PSI
 
 extern struct static_key_false psi_disabled;
+extern struct psi_group psi_system;
 
 void psi_init(void);
 
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 1140357d46f4..217cec4e22c6 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -3540,15 +3540,24 @@ static int cpu_stat_show(struct seq_file *seq, void *v)
 #ifdef CONFIG_PSI
 static int cgroup_io_pressure_show(struct seq_file *seq, void *v)
 {
-        return psi_show(seq, &seq_css(seq)->cgroup->psi, PSI_IO);
+        struct cgroup *cgroup = seq_css(seq)->cgroup;
+        struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
+
+        return psi_show(seq, psi, PSI_IO);
 }
 static int cgroup_memory_pressure_show(struct seq_file *seq, void *v)
 {
-        return psi_show(seq, &seq_css(seq)->cgroup->psi, PSI_MEM);
+        struct cgroup *cgroup = seq_css(seq)->cgroup;
+        struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
+
+        return psi_show(seq, psi, PSI_MEM);
 }
 static int cgroup_cpu_pressure_show(struct seq_file *seq, void *v)
 {
-        return psi_show(seq, &seq_css(seq)->cgroup->psi, PSI_CPU);
+        struct cgroup *cgroup = seq_css(seq)->cgroup;
+        struct psi_group *psi = cgroup->id == 1 ? &psi_system : &cgroup->psi;
+
+        return psi_show(seq, psi, PSI_CPU);
 }
 
 static ssize_t cgroup_pressure_write(struct kernfs_open_file *of, char *buf,
@@ -4801,7 +4810,6 @@ static struct cftype cgroup_base_files[] = {
 #ifdef CONFIG_PSI
         {
                 .name = "io.pressure",
-                .flags = CFTYPE_NOT_ON_ROOT,
                 .seq_show = cgroup_io_pressure_show,
                 .write = cgroup_io_pressure_write,
                 .poll = cgroup_pressure_poll,
@@ -4809,7 +4817,6 @@ static struct cftype cgroup_base_files[] = {
         },
         {
                 .name = "memory.pressure",
-                .flags = CFTYPE_NOT_ON_ROOT,
                 .seq_show = cgroup_memory_pressure_show,
                 .write = cgroup_memory_pressure_write,
                 .poll = cgroup_pressure_poll,
@@ -4817,7 +4824,6 @@ static struct cftype cgroup_base_files[] = {
         },
         {
                 .name = "cpu.pressure",
-                .flags = CFTYPE_NOT_ON_ROOT,
                 .seq_show = cgroup_cpu_pressure_show,
                 .write = cgroup_cpu_pressure_write,
                 .poll = cgroup_pressure_poll,
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index e88918e0bb6d..7acc632c3b82 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -173,7 +173,7 @@ static u64 psi_period __read_mostly;
 
 /* System-level pressure and stall tracking */
 static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu);
-static struct psi_group psi_system = {
+struct psi_group psi_system = {
         .pcpu = &system_group_pcpu,
 };