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[PATCH 2/2] cgroup: reset css on destruction

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  [PATCH 2/2] cgroup: reset css on destruction Vladimir Davydov <vdavydov@virtuozzo.com> - 2016-03-01 12:20 +0100
    Re: [PATCH 2/2] cgroup: reset css on destruction Tejun Heo <tj@kernel.org> - 2016-03-01 17:40 +0100
      Re: [PATCH 2/2] cgroup: reset css on destruction Vladimir Davydov <vdavydov@virtuozzo.com> - 2016-03-01 18:00 +0100
        Re: [PATCH 2/2] cgroup: reset css on destruction Tejun Heo <tj@kernel.org> - 2016-03-01 18:10 +0100
        Re: [PATCH 2/2] cgroup: reset css on destruction Johannes Weiner <hannes@cmpxchg.org> - 2016-03-01 21:00 +0100

#1346533 — [PATCH 2/2] cgroup: reset css on destruction

An associated css can be around for quite a while after a cgroup
directory has been removed. In general, it makes sense to reset it to
defaults so as not to worry about any remnants. For instance, memory
cgroup needs to reset memory.low, otherwise pages charged to a dead
cgroup might never get reclaimed. There's ->css_reset callback, which
would fit perfectly for the purpose. Currently, it's only called when a
subsystem is disabled in the unified hierarchy and there are other
subsystems dependant on it. Let's call it on css destruction as well.

Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>
---
 kernel/cgroup.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index cc40463e7b69..2ef78912c996 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -5138,6 +5138,8 @@ static void kill_css(struct cgroup_subsys_state *css)
 	 * See seq_css() for details.
 	 */
 	css_clear_dir(css, NULL);
+	if (css->ss->css_reset)
+		css->ss->css_reset(css);
 
 	/*
 	 * Killing would put the base ref, but we need to keep it alive
-- 
2.1.4

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#1346743

On Tue, Mar 01, 2016 at 02:13:13PM +0300, Vladimir Davydov wrote:
> @@ -5138,6 +5138,8 @@ static void kill_css(struct cgroup_subsys_state *css)
>  	 * See seq_css() for details.
>  	 */
>  	css_clear_dir(css, NULL);
> +	if (css->ss->css_reset)
> +		css->ss->css_reset(css);

I think the better spot for this is in offline_css() right before
->css_offline() is called.

Thanks.

-- 
tejun

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#1346754

On Tue, Mar 01, 2016 at 11:30:18AM -0500, Tejun Heo wrote:
> On Tue, Mar 01, 2016 at 02:13:13PM +0300, Vladimir Davydov wrote:
> > @@ -5138,6 +5138,8 @@ static void kill_css(struct cgroup_subsys_state *css)
> >  	 * See seq_css() for details.
> >  	 */
> >  	css_clear_dir(css, NULL);
> > +	if (css->ss->css_reset)
> > +		css->ss->css_reset(css);
> 
> I think the better spot for this is in offline_css() right before
> ->css_offline() is called.

Okay, here it goes.
---
From: Vladimir Davydov <vdavydov@virtuozzo.com>
Subject: [PATCH] cgroup: reset css on destruction

An associated css can be around for quite a while after a cgroup
directory has been removed. In general, it makes sense to reset it to
defaults so as not to worry about any remnants. For instance, memory
cgroup needs to reset memory.low, otherwise pages charged to a dead
cgroup might never get reclaimed. There's ->css_reset callback, which
would fit perfectly for the purpose. Currently, it's only called when a
subsystem is disabled in the unified hierarchy and there are other
subsystems dependant on it. Let's call it on css destruction as well.

Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index cc40463e7b69..bb1900b70b01 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4876,6 +4876,9 @@ static void offline_css(struct cgroup_subsys_state *css)
 	if (!(css->flags & CSS_ONLINE))
 		return;
 
+	if (ss->css_reset)
+		ss->css_reset(css);
+
 	if (ss->css_offline)
 		ss->css_offline(css);
 

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#1346763

On Tue, Mar 01, 2016 at 07:56:30PM +0300, Vladimir Davydov wrote:
> From: Vladimir Davydov <vdavydov@virtuozzo.com>
> Subject: [PATCH] cgroup: reset css on destruction
> 
> An associated css can be around for quite a while after a cgroup
> directory has been removed. In general, it makes sense to reset it to
> defaults so as not to worry about any remnants. For instance, memory
> cgroup needs to reset memory.low, otherwise pages charged to a dead
> cgroup might never get reclaimed. There's ->css_reset callback, which
> would fit perfectly for the purpose. Currently, it's only called when a
> subsystem is disabled in the unified hierarchy and there are other
> subsystems dependant on it. Let's call it on css destruction as well.
> 
> Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

Applied to cgroup/for-4.6.  Thanks.

-- 
tejun

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#1346971

On Tue, Mar 01, 2016 at 07:56:30PM +0300, Vladimir Davydov wrote:
> From: Vladimir Davydov <vdavydov@virtuozzo.com>
> Subject: [PATCH] cgroup: reset css on destruction
> 
> An associated css can be around for quite a while after a cgroup
> directory has been removed. In general, it makes sense to reset it to
> defaults so as not to worry about any remnants. For instance, memory
> cgroup needs to reset memory.low, otherwise pages charged to a dead
> cgroup might never get reclaimed. There's ->css_reset callback, which
> would fit perfectly for the purpose. Currently, it's only called when a
> subsystem is disabled in the unified hierarchy and there are other
> subsystems dependant on it. Let's call it on css destruction as well.
> 
> Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Vladimir Davydov <vdavydov@virtuozzo.com>

It's already in a git tree, but FWIW

Acked-by: Johannes Weiner <hannes@cmpxchg.org>

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