[RFC 02/18] cgroup_pids: track maximum pids

[Topi Miettinen]

Track maximum pids in the cgroup, present it in cgroup pids.current_max.

Signed-off-by: Topi Miettinen <toiwo...@gmail.com>
---
 kernel/cgroup_pids.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/kernel/cgroup_pids.c b/kernel/cgroup_pids.c
index 303097b..53fb21d 100644
--- a/kernel/cgroup_pids.c
+++ b/kernel/cgroup_pids.c
@@ -48,6 +48,7 @@ struct pids_cgroup {
         * %PIDS_MAX = (%PID_MAX_LIMIT + 1).
         */
        atomic64_t                      counter;
+       atomic64_t                      cur_max;
        int64_t                         limit;
 };
 
@@ -72,6 +73,7 @@ pids_css_alloc(struct cgroup_subsys_state *parent)
 
        pids->limit = PIDS_MAX;
        atomic64_set(&pids->counter, 0);
+       atomic64_set(&pids->cur_max, 0);
        return &pids->css;
 }
 
@@ -182,6 +184,10 @@ static int pids_can_attach(struct cgroup_taskset *tset)
 
                pids_charge(pids, 1);
                pids_uncharge(old_pids, 1);
+               if (atomic64_read(&pids->cur_max) <
+                   atomic64_read(&pids->counter))
+                       atomic64_set(&pids->cur_max,
+                                    atomic64_read(&pids->counter));
        }
 
        return 0;
@@ -202,6 +208,10 @@ static void pids_cancel_attach(struct cgroup_taskset *tset)
 
                pids_charge(old_pids, 1);
                pids_uncharge(pids, 1);
+               if (atomic64_read(&old_pids->cur_max) <
+                   atomic64_read(&old_pids->counter))
+                       atomic64_set(&old_pids->cur_max,
+                                    atomic64_read(&old_pids->counter));
        }
 }
 
@@ -236,6 +246,14 @@ static void pids_free(struct task_struct *task)
        pids_uncharge(pids, 1);
 }
 
+static void pids_fork(struct task_struct *task)
+{
+       struct pids_cgroup *pids = css_pids(task_css(task, pids_cgrp_id));
+
+       if (atomic64_read(&pids->cur_max) < atomic64_read(&pids->counter))
+               atomic64_set(&pids->cur_max, atomic64_read(&pids->counter));
+}
+
 static ssize_t pids_max_write(struct kernfs_open_file *of, char *buf,
                              size_t nbytes, loff_t off)
 {
@@ -288,6 +306,14 @@ static s64 pids_current_read(struct cgroup_subsys_state 
*css,
        return atomic64_read(&pids->counter);
 }
 
+static s64 pids_current_max_read(struct cgroup_subsys_state *css,
+                                struct cftype *cft)
+{
+       struct pids_cgroup *pids = css_pids(css);
+
+       return atomic64_read(&pids->cur_max);
+}
+
 static struct cftype pids_files[] = {
        {
                .name = "max",
@@ -300,6 +326,11 @@ static struct cftype pids_files[] = {
                .read_s64 = pids_current_read,
                .flags = CFTYPE_NOT_ON_ROOT,
        },
+       {
+               .name = "current_max",
+               .read_s64 = pids_current_max_read,
+               .flags = CFTYPE_NOT_ON_ROOT,
+       },
        { }     /* terminate */
 };
 
@@ -313,4 +344,5 @@ struct cgroup_subsys pids_cgrp_subsys = {
        .free           = pids_free,
        .legacy_cftypes = pids_files,
        .dfl_cftypes    = pids_files,
+       .fork           = pids_fork,
 };
-- 
2.8.1