linux-kernel - Re: [PATCH] Documentation/memcg: warn about incomplete kmemcg state

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Date:	Tue, 22 Apr 2014 11:25:08 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] Documentation/memcg: warn about incomplete kmemcg state

On Mon 21-04-14 11:47:00, Vladimir Davydov wrote:
> Kmemcg is currently under development and lacks some important features.
> In particular, it does not have support of kmem reclaim on memory
> pressure inside cgroup, which practically makes it unusable in real
> life. Let's warn about it in both Kconfig and Documentation to prevent
> complaints arising.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>

Thanks! This should have been merged log time ago...

Acked-by: Michal Hocko <mhocko@...e.cz>

> ---
>  Documentation/cgroups/memory.txt |    5 +++++
>  init/Kconfig                     |    6 ++++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> index 2622115276aa..af3cdfa3c07a 100644
> --- a/Documentation/cgroups/memory.txt
> +++ b/Documentation/cgroups/memory.txt
> @@ -270,6 +270,11 @@ When oom event notifier is registered, event will be delivered.
>  
>  2.7 Kernel Memory Extension (CONFIG_MEMCG_KMEM)
>  
> +WARNING: Current implementation lacks reclaim support. That means allocation
> +	 attempts will fail when close to the limit even if there are plenty of
> +	 kmem available for reclaim. That makes this option unusable in real
> +	 life so DO NOT SELECT IT unless for development purposes.
> +
>  With the Kernel memory extension, the Memory Controller is able to limit
>  the amount of kernel memory used by the system. Kernel memory is fundamentally
>  different than user memory, since it can't be swapped out, which makes it
> diff --git a/init/Kconfig b/init/Kconfig
> index 427ba60d638f..4d6e645c8ad4 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -993,6 +993,12 @@ config MEMCG_KMEM
>  	  the kmem extension can use it to guarantee that no group of processes
>  	  will ever exhaust kernel resources alone.
>  
> +	  WARNING: Current implementation lacks reclaim support. That means
> +	  allocation attempts will fail when close to the limit even if there
> +	  are plenty of kmem available for reclaim. That makes this option
> +	  unusable in real life so DO NOT SELECT IT unless for development
> +	  purposes.
> +
>  config CGROUP_HUGETLB
>  	bool "HugeTLB Resource Controller for Control Groups"
>  	depends on RESOURCE_COUNTERS && HUGETLB_PAGE
> -- 
> 1.7.10.4
> 

-- 
Michal Hocko
SUSE Labs
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