Re: [RFC/PATCH 4/6] memcg: shmem reclaim helper

[Li Zefan <lizf@cn.fujitsu.com>]

KAMEZAWA Hiroyuki wrote:
> A new call, mem_cgroup_shrink_usage() is added for shmem handling
> and removing not usual usage of mem_cgroup_charge/uncharge.
> 
> Now, shmem calls mem_cgroup_charge() just for reclaim some pages from
> mem_cgroup. In general, shmem is used by some process group and not for
> global resource (like file caches). So, it's reasonable to reclaim pages from
> mem_cgroup where shmem is mainly used.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> ---
>  mm/memcontrol.c |   18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> Index: linux-2.6.26-rc2/mm/memcontrol.c
> ===================================================================
> --- linux-2.6.26-rc2.orig/mm/memcontrol.c
> +++ linux-2.6.26-rc2/mm/memcontrol.c
> @@ -783,6 +783,30 @@ static void mem_cgroup_drop_all_pages(st
>  }
>  
>  /*
> + * A call to try to shrink memory usage under specified resource controller.
> + * This is typically used for page reclaiming for shmem for reducing side
> + * effect of page allocation from shmem, which is used by some mem_cgroup.
> + */
> +int mem_cgroup_shrink_usage(struct mm_struct *mm, gfp_t gfp_mask)
> +{
> +	struct mem_cgroup *mem;
> +	int progress = 0;
> +	int retry = MEM_CGROUP_RECLAIM_RETRIES;
> +
> +	rcu_read_lock();
> +	mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
> +	css_get(&mem->css);
> +	rcu_read_unlock();
> +
> +	while(!progress && --retry) {
> +		progress = try_to_free_mem_cgroup_pages(mem, gfp_mask);
> +	}

This is wrong. How about:
	do {
		...
	} while (!progress && --retry);

> +	if (!retry)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
> +/*
>   * This routine traverse page_cgroup in given list and drop them all.
>   * *And* this routine doesn't reclaim page itself, just removes page_cgroup.
>   */