linux-kernel - Re: [PATCH] Documentation/memcg: update memcg/kmem status

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Date:	Tue, 7 Apr 2015 17:13:58 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH] Documentation/memcg: update memcg/kmem status

On Wed 01-04-15 17:30:36, Vladimir Davydov wrote:
> Memcg/kmem reclaim support has been finally merged. Reflect this in the
> documentation.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>

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

> ---
>  Documentation/cgroups/memory.txt |    8 +++-----
>  init/Kconfig                     |    6 ------
>  2 files changed, 3 insertions(+), 11 deletions(-)
> 
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> index a22df3ad35ff..f456b4315e86 100644
> --- a/Documentation/cgroups/memory.txt
> +++ b/Documentation/cgroups/memory.txt
> @@ -275,11 +275,6 @@ 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
> @@ -345,6 +340,9 @@ set:
>      In this case, the admin could set up K so that the sum of all groups is
>      never greater than the total memory, and freely set U at the cost of his
>      QoS.
> +    WARNING: In the current implementation, memory reclaim will NOT be
> +    triggered for a cgroup when it hits K while staying below U, which makes
> +    this setup impractical.
>  
>      U != 0, K >= U:
>      Since kmem charges will also be fed to the user counter and reclaim will be
> diff --git a/init/Kconfig b/init/Kconfig
> index 7766b500f679..caffca37ccb7 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1059,12 +1059,6 @@ 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 HUGETLB_PAGE
> -- 
> 1.7.10.4
> 
> --
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-- 
Michal Hocko
SUSE Labs
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