[RFC PATCH 5/5] refresh VM committed space after a task migration

[RFC PATCH 5/5] refresh VM committed space after a task migration

[Andrea Righi]

Update VM committed space statistics when a task is migrated from a cgroup to
another. To implement this feature we must keep track of the space committed by
each task (that is directly accounted in the task_struct).

Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
---
 include/linux/sched.h |    3 +++
 kernel/fork.c         |    3 +++
 mm/memcontrol.c       |    6 ++++++
 3 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index ae0be3c..8b458df 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1277,6 +1277,9 @@ struct task_struct {
 	/* cg_list protected by css_set_lock and tsk->alloc_lock */
 	struct list_head cg_list;
 #endif
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR
+	atomic_long_t vm_committed_space;
+#endif
 #ifdef CONFIG_FUTEX
 	struct robust_list_head __user *robust_list;
 #ifdef CONFIG_COMPAT
diff --git a/kernel/fork.c b/kernel/fork.c
index eaffa56..9fafbdb 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -219,6 +219,9 @@ static struct task_struct *dup_task_struct(struct task_struct *orig)
 	/* One for us, one for whoever does the "release_task()" (usually parent) */
 	atomic_set(&tsk->usage,2);
 	atomic_set(&tsk->fs_excl, 0);
+#ifdef CONFIG_CGROUP_MEM_RES_CTLR
+	atomic_long_set(&tsk->vm_committed_space, 0);
+#endif
 #ifdef CONFIG_BLK_DEV_IO_TRACE
 	tsk->btrace_seq = 0;
 #endif
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index e3e34e9..bc4923e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1334,6 +1334,7 @@ static void mem_cgroup_move_task(struct cgroup_subsys *ss,
 {
 	struct mm_struct *mm;
 	struct mem_cgroup *mem, *old_mem;
+	long committed;
 
 	if (mem_cgroup_subsys.disabled)
 		return;
@@ -1355,6 +1356,11 @@ static void mem_cgroup_move_task(struct cgroup_subsys *ss,
 	if (!thread_group_leader(p))
 		goto out;
 
+	preempt_disable();
+	committed = atomic_long_read(&p->vm_committed_space);
+	atomic_long_sub(committed, &old_mem->vmacct.vm_committed_space);
+	atomic_long_add(committed, &mem->vmacct.vm_committed_space);
+	preempt_enable();
 out:
 	mmput(mm);
 }
-- 
1.5.4.3

Re: [RFC PATCH 5/5] refresh VM committed space after a task migration

[Dave Hansen]

On Tue, 2008-06-10 at 01:33 +0200, Andrea Righi wrote:
> +       preempt_disable();
> +       committed = atomic_long_read(&p->vm_committed_space);
> +       atomic_long_sub(committed, &old_mem->vmacct.vm_committed_space);
> +       atomic_long_add(committed, &mem->vmacct.vm_committed_space);
> +       preempt_enable();
>  out:
>         mmput(mm);
>  }

Why bother with the preempt stuff here?  What does the actually protect
against?  I assume that you're trying to keep other tasks that might run
on this CPU from seeing weird, inconsistent numbers in here.  Is there
some other looks that keeps *other* cpus from seeing this?

In any case, I think it needs a big, fat comment.

-- Dave

Re: [RFC PATCH 5/5] refresh VM committed space after a task migration

[Andrea Righi]

Dave Hansen wrote:
> On Tue, 2008-06-10 at 01:33 +0200, Andrea Righi wrote:
>> +       preempt_disable();
>> +       committed = atomic_long_read(&p->vm_committed_space);
>> +       atomic_long_sub(committed, &old_mem->vmacct.vm_committed_space);
>> +       atomic_long_add(committed, &mem->vmacct.vm_committed_space);
>> +       preempt_enable();
>>  out:
>>         mmput(mm);
>>  }
> 
> Why bother with the preempt stuff here?  What does the actually protect
> against?  I assume that you're trying to keep other tasks that might run
> on this CPU from seeing weird, inconsistent numbers in here.  Is there
> some other looks that keeps *other* cpus from seeing this?
> 
> In any case, I think it needs a big, fat comment.

Yes, true, mem_cgroup_move_task() is called after the task->cgroups
pointer has been changed. So, even if task changes its committed space
between the atomic_long_sub() and atomic_long_add() it will be correctly
accounted in the new cgroup.

-Andrea