Re: [PATCH][for -mm] Fix and Enhancements for memory cgroup [6/6] add force reclaim interface

[Balbir Singh <balbir@linux.vnet.ibm.com>]

KAMEZAWA Hiroyuki wrote:
> This patch adds an interface "memory.force_reclaim".
> Any write to this file will drop all charges in this cgroup if
> there is no task under.
> 
> %echo 1 > /....../memory.force_reclaim
> 

Looks like a good name, do you think system administrators would
find force_empty more useful?

> will drop all charges of memory cgroup if cgroup's tasks is empty.
> 
> This is useful to invoke rmdir() against memory cgroup successfully.
> 
> Tested and worked well on x86_64/fake-NUMA system.
> 
> Changelog:
>   - added a new interface force_relcaim.
>   - changes spin_lock to spin_lock_irqsave().
> 
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> 
>  mm/memcontrol.c |   79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
> 
> Index: devel-2.6.23-rc8-mm2/mm/memcontrol.c
> ===================================================================
> --- devel-2.6.23-rc8-mm2.orig/mm/memcontrol.c
> +++ devel-2.6.23-rc8-mm2/mm/memcontrol.c
> @@ -507,6 +507,55 @@ retry:
>  	return;
>  }
> 
> +static void
> +mem_cgroup_force_reclaim_list(struct mem_cgroup *mem, struct list_head *list)
> +{
> +	struct page_cgroup *pc;
> +	struct page *page;
> +	int count = SWAP_CLUSTER_MAX;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&mem->lru_lock, flags);
> +

Can we add a comment here stating that this routine reclaims just
from the per cgroup LRU and not from the zone LRU to which the
page belongs.

> +	while (!list_empty(list)) {
> +		pc = list_entry(list->prev, struct page_cgroup, lru);
> +		page = pc->page;
> +		if (clear_page_cgroup(page, pc) == pc) {
> +			css_put(&mem->css);
> +			res_counter_uncharge(&mem->res, PAGE_SIZE);
> +			list_del_init(&pc->lru);
> +			kfree(pc);
> +		} else
> +			count = 1; /* race? ...do relax */
> +
> +		if (--count == 0) {
> +			spin_unlock_irqrestore(&mem->lru_lock, flags);
> +			cond_resched();
> +			spin_lock_irqsave(&mem->lru_lock, flags);
> +			count = SWAP_CLUSTER_MAX;
> +		}
> +	}
> +	spin_unlock_irqrestore(&mem->lru_lock, flags);
> +}
> +
> +int mem_cgroup_force_reclaim(struct mem_cgroup *mem)
> +{
> +	int ret = -EBUSY;
> +	while (!list_empty(&mem->active_list) ||
> +	       !list_empty(&mem->inactive_list)) {
> +		if (atomic_read(&mem->css.cgroup->count) > 0)
> +			goto out;
> +		mem_cgroup_force_reclaim_list(mem, &mem->active_list);
> +		mem_cgroup_force_reclaim_list(mem, &mem->inactive_list);
> +	}
> +	ret = 0;
> +out:
> +	css_put(&mem->css);

We do a css_put() here, did we do a css_get() anywhere?

> +	return ret;
> +}
> +
> +
> +
>  int mem_cgroup_write_strategy(char *buf, unsigned long long *tmp)
>  {
>  	*tmp = memparse(buf, &buf);
> @@ -592,6 +641,31 @@ static ssize_t mem_control_type_read(str
>  			ppos, buf, s - buf);
>  }
> 
> +
> +static ssize_t mem_force_reclaim_write(struct cgroup *cont,
> +				struct cftype *cft, struct file *file,
> +				const char __user *userbuf,
> +				size_t nbytes, loff_t *ppos)
> +{
> +	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
> +	int ret;
> +	ret = mem_cgroup_force_reclaim(mem);
> +	if (!ret)
> +		ret = nbytes;
> +	return ret;
> +}
> +
> +static ssize_t mem_force_reclaim_read(struct cgroup *cont,
> +				struct cftype *cft,
> +				struct file *file, char __user *userbuf,
> +				size_t nbytes, loff_t *ppos)
> +{
> +	char buf[2] = "0";
> +	return simple_read_from_buffer((void __user *)userbuf, nbytes,
> +			ppos, buf, strlen(buf));
> +}
> +
> +
>  static struct cftype mem_cgroup_files[] = {
>  	{
>  		.name = "usage_in_bytes",
> @@ -614,6 +688,11 @@ static struct cftype mem_cgroup_files[] 
>  		.write = mem_control_type_write,
>  		.read = mem_control_type_read,
>  	},
> +	{
> +		.name = "force_reclaim",
> +		.write = mem_force_reclaim_write,
> +		.read = mem_force_reclaim_read,
> +	},
>  };
> 
>  static struct mem_cgroup init_mem_cgroup;
> 
> 


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

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