[PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Sridhar Samudrala]

Add a new kernel API to attach a task to current task's cgroup
in all the active hierarchies.

Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -570,6 +570,7 @@ struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
 void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it);
 int cgroup_scan_tasks(struct cgroup_scanner *scan);
 int cgroup_attach_task(struct cgroup *, struct task_struct *);
+int cgroup_attach_task_current_cg(struct task_struct *);
 
 /*
  * CSS ID is ID for cgroup_subsys_state structs under subsys. This only works
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 6d870f2..6cfeb06 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1788,6 +1788,29 @@ out:
 	return retval;
 }
 
+/**
+ * cgroup_attach_task_current_cg - attach task 'tsk' to current task's cgroup
+ * @tsk: the task to be attached
+ */
+int cgroup_attach_task_current_cg(struct task_struct *tsk)
+{
+	struct cgroupfs_root *root;
+	struct cgroup *cur_cg;
+	int retval = 0;
+
+	cgroup_lock();
+	for_each_active_root(root) {
+		cur_cg = task_cgroup_from_root(current, root);
+		retval = cgroup_attach_task(cur_cg, tsk);
+		if (retval)
+			break;
+	}
+	cgroup_unlock();
+
+	return retval;
+}
+EXPORT_SYMBOL_GPL(cgroup_attach_task_current_cg);
+
 /*
  * Attach task with pid 'pid' to cgroup 'cgrp'. Call with cgroup_mutex
  * held. May take task_lock of task

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Paul Menage]

On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
<samudrala.sridhar@gmail.com> wrote:
> Add a new kernel API to attach a task to current task's cgroup
> in all the active hierarchies.
>
> Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>

Reviewed-by: Paul Menage <menage@google.com>

It would be more efficient to just attach directly to current->cgroups
rather than potentially creating/destroying one css_set for each
hierarchy until we've completely converged on current->cgroups - but
that would require a bunch of refactoring of the guts of
cgroup_attach_task() to ensure that the right can_attach()/attach()
callbacks are made. That doesn't really seem worthwhile right now for
the initial use, that I imagine isn't going to be
performance-sensitive.

Paul

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Paul Menage]

On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
<samudrala.sridhar@gmail.com> wrote:
> Add a new kernel API to attach a task to current task's cgroup
> in all the active hierarchies.
>
> Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>

Reviewed-by: Paul Menage <menage@google.com>

It would be more efficient to just attach directly to current->cgroups
rather than potentially creating/destroying one css_set for each
hierarchy until we've completely converged on current->cgroups - but
that would require a bunch of refactoring of the guts of
cgroup_attach_task() to ensure that the right can_attach()/attach()
callbacks are made. That doesn't really seem worthwhile right now for
the initial use, that I imagine isn't going to be
performance-sensitive.

Paul

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Paul Menage]

On Thu, May 20, 2010 at 3:22 PM, Paul Menage <menage@google.com> wrote:
> On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
> <samudrala.sridhar@gmail.com> wrote:
>> Add a new kernel API to attach a task to current task's cgroup
>> in all the active hierarchies.
>>
>> Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
>
> Reviewed-by: Paul Menage <menage@google.com>
>

One other thought on this - this would be the first piece of code
that's attaching a task to a cgroup without holding the cgroup
directory inode i_mutex. I believe that this is probably OK.

Paul

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Paul Menage]

On Thu, May 20, 2010 at 3:22 PM, Paul Menage <menage@google.com> wrote:
> On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
> <samudrala.sridhar@gmail.com> wrote:
>> Add a new kernel API to attach a task to current task's cgroup
>> in all the active hierarchies.
>>
>> Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
>
> Reviewed-by: Paul Menage <menage@google.com>
>

One other thought on this - this would be the first piece of code
that's attaching a task to a cgroup without holding the cgroup
directory inode i_mutex. I believe that this is probably OK.

Paul

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Sridhar Samudrala]

On 5/20/2010 3:22 PM, Paul Menage wrote:
> On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
> <samudrala.sridhar@gmail.com>  wrote:
>    
>> Add a new kernel API to attach a task to current task's cgroup
>> in all the active hierarchies.
>>
>> Signed-off-by: Sridhar Samudrala<sri@us.ibm.com>
>>      
> Reviewed-by: Paul Menage<menage@google.com>
>
> It would be more efficient to just attach directly to current->cgroups
> rather than potentially creating/destroying one css_set for each
> hierarchy until we've completely converged on current->cgroups - but
> that would require a bunch of refactoring of the guts of
> cgroup_attach_task() to ensure that the right can_attach()/attach()
> callbacks are made. That doesn't really seem worthwhile right now for
> the initial use, that I imagine isn't going to be
> performance-sensitive.
>    
Yes. In our use-case, this will be called only once per guest interface 
when the guest comes up.
Hope you or someone more familiar with cgroups subsystem can optimize 
this function later.

Thanks
Sridhar

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Michael S. Tsirkin]

On Thu, May 20, 2010 at 03:22:15PM -0700, Paul Menage wrote:
> On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
> <samudrala.sridhar@gmail.com> wrote:
> > Add a new kernel API to attach a task to current task's cgroup
> > in all the active hierarchies.
> >
> > Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
> 
> Reviewed-by: Paul Menage <menage@google.com>
> 
> It would be more efficient to just attach directly to current->cgroups
> rather than potentially creating/destroying one css_set for each
> hierarchy until we've completely converged on current->cgroups - but
> that would require a bunch of refactoring of the guts of
> cgroup_attach_task() to ensure that the right can_attach()/attach()
> callbacks are made. That doesn't really seem worthwhile right now for
> the initial use, that I imagine isn't going to be
> performance-sensitive.
> 
> Paul

Is this patch suitable for 2.6.35?
It is needed to fix the case where vhost user might cause a kernel thread
to consume more CPU than allowed by the cgroup.
Should I just merge it through the vhost tree?
Ack for this?

Thanks,

-- 
MST

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Paul Menage]

On Tue, May 25, 2010 at 9:53 AM, Michael S. Tsirkin <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> On Thu, May 20, 2010 at 03:22:15PM -0700, Paul Menage wrote:
>> On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
>> <samudrala.sridhar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> > Add a new kernel API to attach a task to current task's cgroup
>> > in all the active hierarchies.
>> >
>> > Signed-off-by: Sridhar Samudrala <sri-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
>>
>> Reviewed-by: Paul Menage <menage-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
>>
>> It would be more efficient to just attach directly to current->cgroups
>> rather than potentially creating/destroying one css_set for each
>> hierarchy until we've completely converged on current->cgroups - but
>> that would require a bunch of refactoring of the guts of
>> cgroup_attach_task() to ensure that the right can_attach()/attach()
>> callbacks are made. That doesn't really seem worthwhile right now for
>> the initial use, that I imagine isn't going to be
>> performance-sensitive.
>>
>> Paul
>
> Is this patch suitable for 2.6.35?

Should be OK, yes.

Paul

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Paul Menage]

On Tue, May 25, 2010 at 9:53 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Thu, May 20, 2010 at 03:22:15PM -0700, Paul Menage wrote:
>> On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
>> <samudrala.sridhar@gmail.com> wrote:
>> > Add a new kernel API to attach a task to current task's cgroup
>> > in all the active hierarchies.
>> >
>> > Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
>>
>> Reviewed-by: Paul Menage <menage@google.com>
>>
>> It would be more efficient to just attach directly to current->cgroups
>> rather than potentially creating/destroying one css_set for each
>> hierarchy until we've completely converged on current->cgroups - but
>> that would require a bunch of refactoring of the guts of
>> cgroup_attach_task() to ensure that the right can_attach()/attach()
>> callbacks are made. That doesn't really seem worthwhile right now for
>> the initial use, that I imagine isn't going to be
>> performance-sensitive.
>>
>> Paul
>
> Is this patch suitable for 2.6.35?

Should be OK, yes.

Paul

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Paul Menage]

On Tue, May 25, 2010 at 9:53 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> On Thu, May 20, 2010 at 03:22:15PM -0700, Paul Menage wrote:
>> On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
>> <samudrala.sridhar@gmail.com> wrote:
>> > Add a new kernel API to attach a task to current task's cgroup
>> > in all the active hierarchies.
>> >
>> > Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
>>
>> Reviewed-by: Paul Menage <menage@google.com>
>>
>> It would be more efficient to just attach directly to current->cgroups
>> rather than potentially creating/destroying one css_set for each
>> hierarchy until we've completely converged on current->cgroups - but
>> that would require a bunch of refactoring of the guts of
>> cgroup_attach_task() to ensure that the right can_attach()/attach()
>> callbacks are made. That doesn't really seem worthwhile right now for
>> the initial use, that I imagine isn't going to be
>> performance-sensitive.
>>
>> Paul
>
> Is this patch suitable for 2.6.35?

Should be OK, yes.

Paul

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Michael S. Tsirkin]

On Tue, May 25, 2010 at 11:34:12AM -0700, Paul Menage wrote:
> On Tue, May 25, 2010 at 9:53 AM, Michael S. Tsirkin <mst@redhat.com> wrote:
> > On Thu, May 20, 2010 at 03:22:15PM -0700, Paul Menage wrote:
> >> On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
> >> <samudrala.sridhar@gmail.com> wrote:
> >> > Add a new kernel API to attach a task to current task's cgroup
> >> > in all the active hierarchies.
> >> >
> >> > Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
> >>
> >> Reviewed-by: Paul Menage <menage@google.com>
> >>
> >> It would be more efficient to just attach directly to current->cgroups
> >> rather than potentially creating/destroying one css_set for each
> >> hierarchy until we've completely converged on current->cgroups - but
> >> that would require a bunch of refactoring of the guts of
> >> cgroup_attach_task() to ensure that the right can_attach()/attach()
> >> callbacks are made. That doesn't really seem worthwhile right now for
> >> the initial use, that I imagine isn't going to be
> >> performance-sensitive.
> >>
> >> Paul
> >
> > Is this patch suitable for 2.6.35?
> 
> Should be OK, yes.
> 
> Paul

So I'll add your Acked-by tag then, and merge through the vhost tree
together with the patch that uses this.

-- 
MST

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Michael S. Tsirkin]

On Tue, May 25, 2010 at 11:34:12AM -0700, Paul Menage wrote:
> On Tue, May 25, 2010 at 9:53 AM, Michael S. Tsirkin <mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
> > On Thu, May 20, 2010 at 03:22:15PM -0700, Paul Menage wrote:
> >> On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
> >> <samudrala.sridhar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> >> > Add a new kernel API to attach a task to current task's cgroup
> >> > in all the active hierarchies.
> >> >
> >> > Signed-off-by: Sridhar Samudrala <sri-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
> >>
> >> Reviewed-by: Paul Menage <menage-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> >>
> >> It would be more efficient to just attach directly to current->cgroups
> >> rather than potentially creating/destroying one css_set for each
> >> hierarchy until we've completely converged on current->cgroups - but
> >> that would require a bunch of refactoring of the guts of
> >> cgroup_attach_task() to ensure that the right can_attach()/attach()
> >> callbacks are made. That doesn't really seem worthwhile right now for
> >> the initial use, that I imagine isn't going to be
> >> performance-sensitive.
> >>
> >> Paul
> >
> > Is this patch suitable for 2.6.35?
> 
> Should be OK, yes.
> 
> Paul

So I'll add your Acked-by tag then, and merge through the vhost tree
together with the patch that uses this.

-- 
MST

Re: [PATCH 1/3] cgroups: Add an API to attach a task to current task's cgroup

[Michael S. Tsirkin]

On Thu, May 20, 2010 at 03:22:15PM -0700, Paul Menage wrote:
> On Tue, May 18, 2010 at 5:04 PM, Sridhar Samudrala
> <samudrala.sridhar-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > Add a new kernel API to attach a task to current task's cgroup
> > in all the active hierarchies.
> >
> > Signed-off-by: Sridhar Samudrala <sri-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
> 
> Reviewed-by: Paul Menage <menage-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> 
> It would be more efficient to just attach directly to current->cgroups
> rather than potentially creating/destroying one css_set for each
> hierarchy until we've completely converged on current->cgroups - but
> that would require a bunch of refactoring of the guts of
> cgroup_attach_task() to ensure that the right can_attach()/attach()
> callbacks are made. That doesn't really seem worthwhile right now for
> the initial use, that I imagine isn't going to be
> performance-sensitive.
> 
> Paul

Is this patch suitable for 2.6.35?
It is needed to fix the case where vhost user might cause a kernel thread
to consume more CPU than allowed by the cgroup.
Should I just merge it through the vhost tree?
Ack for this?

Thanks,

-- 
MST