Re: [PATCH v4] mm/memcg: try harder to decrease [memory,memsw].limit_in_bytes

[Michal Hocko]

On Wed 10-01-18 15:43:17, Andrey Ryabinin wrote:
[...]
> @@ -2506,15 +2480,13 @@ static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
>  		if (!ret)
>  			break;
>  
> -		try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, !memsw);
> -
> -		curusage = page_counter_read(counter);
> -		/* Usage is reduced ? */
> -		if (curusage >= oldusage)
> -			retry_count--;
> -		else
> -			oldusage = curusage;
> -	} while (retry_count);
> +		usage = page_counter_read(counter);
> +		if (!try_to_free_mem_cgroup_pages(memcg, usage - limit,
> +						GFP_KERNEL, !memsw)) {

If the usage drops below limit in the meantime then you get underflow
and reclaim the whole memcg. I do not think this is a good idea. This
can also lead to over reclaim. Why don't you simply stick with the
original SWAP_CLUSTER_MAX (aka 1 for try_to_free_mem_cgroup_pages)?

> +			ret = -EBUSY;
> +			break;
> +		}
> +	} while (true);

-- 
Michal Hocko
SUSE Labs