cpuset: record old_mems_allowed in struct cpuset

When we update a cpuset's mems_allowed and thus update tasks'
mems_allowed, it's required to pass the old mems_allowed and new
mems_allowed to cpuset_migrate_mm().

Currently we save old mems_allowed in a temp local variable before
changing cpuset->mems_allowed. This patch changes it by saving
old mems_allowed in cpuset->old_mems_allowed.

This currently won't change any behavior, but it will later allow
us to keep tasks in empty cpusets.

v3: restored "cpuset_attach_nodemask_to = cs->mems_allowed"

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 36 insertions, 25 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 608fe1308b22..2b4554588a04 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -88,6 +88,18 @@ struct cpuset {
         cpumask_var_t cpus_allowed;     /* CPUs allowed to tasks in cpuset */
         nodemask_t mems_allowed;        /* Memory Nodes allowed to tasks */
 
+        /*
+         * This is old Memory Nodes tasks took on.
+         *
+         * - top_cpuset.old_mems_allowed is initialized to mems_allowed.
+         * - A new cpuset's old_mems_allowed is initialized when some
+         *   task is moved into it.
+         * - old_mems_allowed is used in cpuset_migrate_mm() when we change
+         *   cpuset.mems_allowed and have tasks' nodemask updated, and
+         *   then old_mems_allowed is updated to mems_allowed.
+         */
+        nodemask_t old_mems_allowed;
+
         struct fmeter fmeter;           /* memory_pressure filter */
 
         /*
@@ -972,16 +984,12 @@ static void cpuset_change_task_nodemask(struct task_struct *tsk,
 static void cpuset_change_nodemask(struct task_struct *p,
                                    struct cgroup_scanner *scan)
 {
+        struct cpuset *cs = cgroup_cs(scan->cg);
         struct mm_struct *mm;
-        struct cpuset *cs;
         int migrate;
-        const nodemask_t *oldmem = scan->data;
-        static nodemask_t newmems;      /* protected by cpuset_mutex */
-
-        cs = cgroup_cs(scan->cg);
-        guarantee_online_mems(cs, &newmems);
+        nodemask_t *newmems = scan->data;
 
-        cpuset_change_task_nodemask(p, &newmems);
+        cpuset_change_task_nodemask(p, newmems);
 
         mm = get_task_mm(p);
         if (!mm)
@@ -991,7 +999,7 @@ static void cpuset_change_nodemask(struct task_struct *p,
 
         mpol_rebind_mm(mm, &cs->mems_allowed);
         if (migrate)
-                cpuset_migrate_mm(mm, oldmem, &cs->mems_allowed);
+                cpuset_migrate_mm(mm, &cs->old_mems_allowed, newmems);
         mmput(mm);
 }
 
@@ -1000,25 +1008,26 @@ static void *cpuset_being_rebound;
 /**
  * update_tasks_nodemask - Update the nodemasks of tasks in the cpuset.
  * @cs: the cpuset in which each task's mems_allowed mask needs to be changed
- * @oldmem: old mems_allowed of cpuset cs
  * @heap: if NULL, defer allocating heap memory to cgroup_scan_tasks()
  *
  * Called with cpuset_mutex held
  * No return value. It's guaranteed that cgroup_scan_tasks() always returns 0
  * if @heap != NULL.
  */
-static void update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem,
-                                 struct ptr_heap *heap)
+static void update_tasks_nodemask(struct cpuset *cs, struct ptr_heap *heap)
 {
+        static nodemask_t newmems;      /* protected by cpuset_mutex */
         struct cgroup_scanner scan;
 
         cpuset_being_rebound = cs;              /* causes mpol_dup() rebind */
 
+        guarantee_online_mems(cs, &newmems);
+
         scan.cg = cs->css.cgroup;
         scan.test_task = NULL;
         scan.process_task = cpuset_change_nodemask;
         scan.heap = heap;
-        scan.data = (nodemask_t *)oldmem;
+        scan.data = &newmems;
 
         /*
          * The mpol_rebind_mm() call takes mmap_sem, which we couldn't
@@ -1032,6 +1041,12 @@ static void update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem,
          */
         cgroup_scan_tasks(&scan);
 
+        /*
+         * All the tasks' nodemasks have been updated, update
+         * cs->old_mems_allowed.
+         */
+        cs->old_mems_allowed = newmems;
+
         /* We're done rebinding vmas to this cpuset's new mems_allowed. */
         cpuset_being_rebound = NULL;
 }
@@ -1052,13 +1067,9 @@ static void update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem,
 static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
                            const char *buf)
 {
-        NODEMASK_ALLOC(nodemask_t, oldmem, GFP_KERNEL);
         int retval;
         struct ptr_heap heap;
 
-        if (!oldmem)
-                return -ENOMEM;
-
         /*
          * top_cpuset.mems_allowed tracks node_stats[N_MEMORY];
          * it's read-only
@@ -1087,8 +1098,8 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
                         goto done;
                 }
         }
-        *oldmem = cs->mems_allowed;
-        if (nodes_equal(*oldmem, trialcs->mems_allowed)) {
+
+        if (nodes_equal(cs->mems_allowed, trialcs->mems_allowed)) {
                 retval = 0;             /* Too easy - nothing to do */
                 goto done;
         }
@@ -1104,11 +1115,10 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
         cs->mems_allowed = trialcs->mems_allowed;
         mutex_unlock(&callback_mutex);
 
-        update_tasks_nodemask(cs, oldmem, &heap);
+        update_tasks_nodemask(cs, &heap);
 
         heap_free(&heap);
 done:
-        NODEMASK_FREE(oldmem);
         return retval;
 }
 
@@ -1431,6 +1441,8 @@ static void cpuset_attach(struct cgroup *cgrp, struct cgroup_taskset *tset)
                 mmput(mm);
         }
 
+        cs->old_mems_allowed = cpuset_attach_nodemask_to;
+
         cs->attach_in_progress--;
         if (!cs->attach_in_progress)
                 wake_up(&cpuset_attach_wq);
@@ -1985,7 +1997,7 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
 static void cpuset_hotplug_update_tasks(struct cpuset *cs)
 {
         static cpumask_t off_cpus;
-        static nodemask_t off_mems, tmp_mems;
+        static nodemask_t off_mems;
         bool is_empty;
 
 retry:
@@ -2015,11 +2027,10 @@ retry:
 
         /* remove offline mems from @cs */
         if (!nodes_empty(off_mems)) {
-                tmp_mems = cs->mems_allowed;
                 mutex_lock(&callback_mutex);
                 nodes_andnot(cs->mems_allowed, cs->mems_allowed, off_mems);
                 mutex_unlock(&callback_mutex);
-                update_tasks_nodemask(cs, &tmp_mems, NULL);
+                update_tasks_nodemask(cs, NULL);
         }
 
         is_empty = cpumask_empty(cs->cpus_allowed) ||
@@ -2083,11 +2094,10 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
 
         /* synchronize mems_allowed to N_MEMORY */
         if (mems_updated) {
-                tmp_mems = top_cpuset.mems_allowed;
                 mutex_lock(&callback_mutex);
                 top_cpuset.mems_allowed = new_mems;
                 mutex_unlock(&callback_mutex);
-                update_tasks_nodemask(&top_cpuset, &tmp_mems, NULL);
+                update_tasks_nodemask(&top_cpuset, NULL);
         }
 
         mutex_unlock(&cpuset_mutex);
@@ -2158,6 +2168,7 @@ void __init cpuset_init_smp(void)
 {
         cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
         top_cpuset.mems_allowed = node_states[N_MEMORY];
+        top_cpuset.old_mems_allowed = top_cpuset.mems_allowed;
 
         register_hotmemory_notifier(&cpuset_track_online_nodes_nb);
 }