[PATCH] memcg: fix return value of mem_cgroup_hierarchy_write()

[PATCH] memcg: fix return value of mem_cgroup_hierarchy_write()

[Li Zefan]

When there are sub-dirs, writing to memory.use_hierarchy returns -EBUSY,
this doesn't seem to fit the meaning of EBUSY, and is inconsistent with
memory.swappiness, which returns -EINVAL in this case.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 mm/memcontrol.c |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index bc8f101..2497f7d 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1760,6 +1760,9 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
 	struct cgroup *parent = cont->parent;
 	struct mem_cgroup *parent_mem = NULL;
 
+	if (val != 0 && val != 1)
+		return -EINVAL;
+
 	if (parent)
 		parent_mem = mem_cgroup_from_cont(parent);
 
@@ -1773,12 +1776,9 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
 	 * set if there are no children.
 	 */
 	if ((!parent_mem || !parent_mem->use_hierarchy) &&
-				(val == 1 || val == 0)) {
-		if (list_empty(&cont->children))
+	    list_empty(&cont->children))
 			mem->use_hierarchy = val;
-		else
-			retval = -EBUSY;
-	} else
+	else
 		retval = -EINVAL;
 	cgroup_unlock();
 
-- 
1.5.4.rc3

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Re: [PATCH] memcg: fix return value of mem_cgroup_hierarchy_write()

[KAMEZAWA Hiroyuki]

On Wed, 14 Jan 2009 16:10:52 +0800
Li Zefan <lizf@cn.fujitsu.com> wrote:

> When there are sub-dirs, writing to memory.use_hierarchy returns -EBUSY,
> this doesn't seem to fit the meaning of EBUSY, and is inconsistent with
> memory.swappiness, which returns -EINVAL in this case.
> 

Hmm...I'm not sure what error code is the best.

In usual, -EINVAL means parameter to write() is bad. In this case, it isn't.

Considering that, -EBUSY seems ok at returning error because of children.
How about change swappiness to return -EBUSY ?

Thanks,
-Kame






> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
>  mm/memcontrol.c |   10 +++++-----
>  1 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index bc8f101..2497f7d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1760,6 +1760,9 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
>  	struct cgroup *parent = cont->parent;
>  	struct mem_cgroup *parent_mem = NULL;
>  
> +	if (val != 0 && val != 1)
> +		return -EINVAL;
> +
>  	if (parent)
>  		parent_mem = mem_cgroup_from_cont(parent);
>  
> @@ -1773,12 +1776,9 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
>  	 * set if there are no children.
>  	 */
>  	if ((!parent_mem || !parent_mem->use_hierarchy) &&
> -				(val == 1 || val == 0)) {
> -		if (list_empty(&cont->children))
> +	    list_empty(&cont->children))
>  			mem->use_hierarchy = val;
> -		else
> -			retval = -EBUSY;
> -	} else
> +	else
>  		retval = -EINVAL;
>  	cgroup_unlock();
>  
> -- 
> 1.5.4.rc3
> 

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Re: [PATCH] memcg: fix return value of mem_cgroup_hierarchy_write()

[Daisuke Nishimura]

On Wed, 14 Jan 2009 16:10:52 +0800, Li Zefan <lizf@cn.fujitsu.com> wrote:
> When there are sub-dirs, writing to memory.use_hierarchy returns -EBUSY,
> this doesn't seem to fit the meaning of EBUSY, and is inconsistent with
> memory.swappiness, which returns -EINVAL in this case.
> 
I also think -EBUSY is not so bad in this case.

Thanks,
Daisuke Nishimura.

> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
>  mm/memcontrol.c |   10 +++++-----
>  1 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index bc8f101..2497f7d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1760,6 +1760,9 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
>  	struct cgroup *parent = cont->parent;
>  	struct mem_cgroup *parent_mem = NULL;
>  
> +	if (val != 0 && val != 1)
> +		return -EINVAL;
> +
>  	if (parent)
>  		parent_mem = mem_cgroup_from_cont(parent);
>  
> @@ -1773,12 +1776,9 @@ static int mem_cgroup_hierarchy_write(struct cgroup *cont, struct cftype *cft,
>  	 * set if there are no children.
>  	 */
>  	if ((!parent_mem || !parent_mem->use_hierarchy) &&
> -				(val == 1 || val == 0)) {
> -		if (list_empty(&cont->children))
> +	    list_empty(&cont->children))
>  			mem->use_hierarchy = val;
> -		else
> -			retval = -EBUSY;
> -	} else
> +	else
>  		retval = -EINVAL;
>  	cgroup_unlock();
>  
> -- 
> 1.5.4.rc3

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Re: [PATCH] memcg: fix return value of mem_cgroup_hierarchy_write()

[Balbir Singh]

* Li Zefan <lizf@cn.fujitsu.com> [2009-01-14 16:10:52]:

> When there are sub-dirs, writing to memory.use_hierarchy returns -EBUSY,
> this doesn't seem to fit the meaning of EBUSY, and is inconsistent with
> memory.swappiness, which returns -EINVAL in this case.
> 
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

The patch does much more than the changelog says. The reason for EBUSY
is that the group is in use due to children or existing references and
tasks. I think EBUSY is the correct error code to return.

-- 
	Balbir

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Re: [PATCH] memcg: fix return value of mem_cgroup_hierarchy_write()

[Li Zefan]

Balbir Singh wrote:
> * Li Zefan <lizf@cn.fujitsu.com> [2009-01-14 16:10:52]:
> 
>> When there are sub-dirs, writing to memory.use_hierarchy returns -EBUSY,
>> this doesn't seem to fit the meaning of EBUSY, and is inconsistent with
>> memory.swappiness, which returns -EINVAL in this case.
>>
>> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> 
> The patch does much more than the changelog says. The reason for EBUSY
> is that the group is in use due to children or existing references and
> tasks. I think EBUSY is the correct error code to return.
> 

Sounds reasonable for me. Thanks.

Regards
Li Zefan

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