linux-kernel - Re: [PATCH 2/2] mm/cgroup: delay soft limit data allocation

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Message-ID: <20170223011644.GB8841@balbir.ozlabs.ibm.com>
Date:   Thu, 23 Feb 2017 12:16:44 +1100
From:   Balbir Singh <bsingharora@...il.com>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm/cgroup: delay soft limit data allocation

On Wed, Feb 22, 2017 at 04:58:11PM +0100, Laurent Dufour wrote:
> Until a soft limit is set to a cgroup, the soft limit data are useless
> so delay this allocation when a limit is set.
> 
> Suggested-by: Michal Hocko <mhocko@...nel.org>
> Signed-off-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
> ---
<snip>
> @@ -3000,6 +3035,8 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
>  		}
>  		break;
>  	case RES_SOFT_LIMIT:
> +		if (!soft_limit_initialized)
> +			soft_limit_initialize();

What happens if this fails? Do we disable this interface?
It's a good idea, but I wonder if we can deal with certain
memory cgroups not supporting soft limits due to memory
shortage at the time of using them.

>  		memcg->soft_limit = nr_pages;
>  		ret = 0;
>  		break;

Balbir Singh.