[PATCH 2/3] memcg: put a restriction on writing memory.force_empty

[PATCH 2/3] memcg: put a restriction on writing memory.force_empty

[Li Zefan]

We can write whatever to memory.force_empty:

        echo 999 > memory.force_empty
        echo wow > memory.force_empty

This is odd, so let's make '1' to be the only valid value.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 mm/memcontrol.c |   21 ++++++++++++---------
 1 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index eb681a6..6145031 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -868,15 +868,18 @@ static ssize_t mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
 				mem_cgroup_write_strategy);
 }
 
-static ssize_t mem_force_empty_write(struct cgroup *cont,
-				struct cftype *cft, struct file *file,
-				const char __user *userbuf,
-				size_t nbytes, loff_t *ppos)
+static int mem_force_empty_write(struct cgroup *cont, struct cftype *cft,
+				 u64 val)
 {
-	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
-	int ret = mem_cgroup_force_empty(mem);
-	if (!ret)
-		ret = nbytes;
+	struct mem_cgroup *mem;
+	int ret;
+
+	if (val != 1)
+		return -EINVAL;
+
+	mem = mem_cgroup_from_cont(cont);
+	ret = mem_cgroup_force_empty(mem);
+
 	return ret;
 }
 
@@ -935,7 +938,7 @@ static struct cftype mem_cgroup_files[] = {
 	},
 	{
 		.name = "force_empty",
-		.write = mem_force_empty_write,
+		.write_u64 = mem_force_empty_write,
 	},
 	{
 		.name = "stat",
-- 
1.5.4.rc3

Re: [PATCH 2/3] memcg: put a restriction on writing memory.force_empty

[Balbir Singh]

Li Zefan wrote:
> We can write whatever to memory.force_empty:
> 
>         echo 999 > memory.force_empty
>         echo wow > memory.force_empty
> 
> This is odd, so let's make '1' to be the only valid value.

I suspect as long as there is no unreasonable side-effect, writing 999 or wow
should be OK.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL

Re: [PATCH 2/3] memcg: put a restriction on writing memory.force_empty

[KAMEZAWA Hiroyuki]

On Tue, 11 Mar 2008 15:45:06 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> Li Zefan wrote:
> > We can write whatever to memory.force_empty:
> > 
> >         echo 999 > memory.force_empty
> >         echo wow > memory.force_empty
> > 
> > This is odd, so let's make '1' to be the only valid value.
> 
> I suspect as long as there is no unreasonable side-effect, writing 999 or wow
> should be OK.
> 
I agree with Balbir.

Thanks,
-Kame