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

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Message-Id: <d301eb31-9c95-60c2-3d41-fc2fcb53f2eb@linux.vnet.ibm.com>
Date:   Thu, 23 Feb 2017 10:15:03 +0100
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     Balbir Singh <bsingharora@...il.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 23/02/2017 02:16, Balbir Singh wrote:
> 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.

Thanks Balbir for the review.

Regarding this point, Michal sent a new proposal which will return
-ENOMEM in the case the initialization failed. I'll send a new series in
that way.

> 
>>  		memcg->soft_limit = nr_pages;
>>  		ret = 0;
>>  		break;
> 
> Balbir Singh.
>