cpuset: rewrite update_tasks_nodemask()

This patch uses cgroup_scan_tasks() to rebind tasks' vmas to new cpuset's
mems_allowed.

Not only simplify the code largely, but also avoid allocating an array to
hold mm pointers of all the tasks in the cpuset.  This array can be big
(size > PAGESIZE) if we have lots of tasks in that cpuset, thus has a
chance to fail the allocation when under memory stress.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 39 insertions, 70 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 31737957cb62..dca455e0482e 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1026,6 +1026,31 @@ static void cpuset_migrate_mm(struct mm_struct *mm, const nodemask_t *from,
         mutex_unlock(&callback_mutex);
 }
 
+/*
+ * Rebind task's vmas to cpuset's new mems_allowed, and migrate pages to new
+ * nodes if memory_migrate flag is set. Called with cgroup_mutex held.
+ */
+static void cpuset_change_nodemask(struct task_struct *p,
+                                   struct cgroup_scanner *scan)
+{
+        struct mm_struct *mm;
+        struct cpuset *cs;
+        int migrate;
+        const nodemask_t *oldmem = scan->data;
+
+        mm = get_task_mm(p);
+        if (!mm)
+                return;
+
+        cs = cgroup_cs(scan->cg);
+        migrate = is_memory_migrate(cs);
+
+        mpol_rebind_mm(mm, &cs->mems_allowed);
+        if (migrate)
+                cpuset_migrate_mm(mm, oldmem, &cs->mems_allowed);
+        mmput(mm);
+}
+
 static void *cpuset_being_rebound;
 
 /**
@@ -1038,88 +1063,32 @@ static void *cpuset_being_rebound;
  */
 static int update_tasks_nodemask(struct cpuset *cs, const nodemask_t *oldmem)
 {
-        struct task_struct *p;
-        struct mm_struct **mmarray;
-        int i, n, ntasks;
-        int migrate;
-        int fudge;
-        struct cgroup_iter it;
         int retval;
+        struct cgroup_scanner scan;
 
         cpuset_being_rebound = cs;              /* causes mpol_dup() rebind */
 
-        fudge = 10;                             /* spare mmarray[] slots */
-        fudge += cpumask_weight(cs->cpus_allowed);/* imagine 1 fork-bomb/cpu */
-        retval = -ENOMEM;
-
-        /*
-         * Allocate mmarray[] to hold mm reference for each task
-         * in cpuset cs.  Can't kmalloc GFP_KERNEL while holding
-         * tasklist_lock.  We could use GFP_ATOMIC, but with a
-         * few more lines of code, we can retry until we get a big
-         * enough mmarray[] w/o using GFP_ATOMIC.
-         */
-        while (1) {
-                ntasks = cgroup_task_count(cs->css.cgroup);  /* guess */
-                ntasks += fudge;
-                mmarray = kmalloc(ntasks * sizeof(*mmarray), GFP_KERNEL);
-                if (!mmarray)
-                        goto done;
-                read_lock(&tasklist_lock);              /* block fork */
-                if (cgroup_task_count(cs->css.cgroup) <= ntasks)
-                        break;                          /* got enough */
-                read_unlock(&tasklist_lock);            /* try again */
-                kfree(mmarray);
-        }
-
-        n = 0;
-
-        /* Load up mmarray[] with mm reference for each task in cpuset. */
-        cgroup_iter_start(cs->css.cgroup, &it);
-        while ((p = cgroup_iter_next(cs->css.cgroup, &it))) {
-                struct mm_struct *mm;
-
-                if (n >= ntasks) {
-                        printk(KERN_WARNING
-                                "Cpuset mempolicy rebind incomplete.\n");
-                        break;
-                }
-                mm = get_task_mm(p);
-                if (!mm)
-                        continue;
-                mmarray[n++] = mm;
-        }
-        cgroup_iter_end(cs->css.cgroup, &it);
-        read_unlock(&tasklist_lock);
+        scan.cg = cs->css.cgroup;
+        scan.test_task = NULL;
+        scan.process_task = cpuset_change_nodemask;
+        scan.heap = NULL;
+        scan.data = (nodemask_t *)oldmem;
 
         /*
-         * Now that we've dropped the tasklist spinlock, we can
-         * rebind the vma mempolicies of each mm in mmarray[] to their
-         * new cpuset, and release that mm.  The mpol_rebind_mm()
-         * call takes mmap_sem, which we couldn't take while holding
-         * tasklist_lock.  Forks can happen again now - the mpol_dup()
-         * cpuset_being_rebound check will catch such forks, and rebind
-         * their vma mempolicies too.  Because we still hold the global
-         * cgroup_mutex, we know that no other rebind effort will
-         * be contending for the global variable cpuset_being_rebound.
+         * The mpol_rebind_mm() call takes mmap_sem, which we couldn't
+         * take while holding tasklist_lock.  Forks can happen - the
+         * mpol_dup() cpuset_being_rebound check will catch such forks,
+         * and rebind their vma mempolicies too.  Because we still hold
+         * the global cgroup_mutex, we know that no other rebind effort
+         * will be contending for the global variable cpuset_being_rebound.
          * It's ok if we rebind the same mm twice; mpol_rebind_mm()
          * is idempotent.  Also migrate pages in each mm to new nodes.
          */
-        migrate = is_memory_migrate(cs);
-        for (i = 0; i < n; i++) {
-                struct mm_struct *mm = mmarray[i];
-
-                mpol_rebind_mm(mm, &cs->mems_allowed);
-                if (migrate)
-                        cpuset_migrate_mm(mm, oldmem, &cs->mems_allowed);
-                mmput(mm);
-        }
+        retval = cgroup_scan_tasks(&scan);
 
         /* We're done rebinding vmas to this cpuset's new mems_allowed. */
-        kfree(mmarray);
         cpuset_being_rebound = NULL;
-        retval = 0;
-done:
+
         return retval;
 }