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Date:	Mon, 28 Nov 2011 11:24:41 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, lizf@...fujitsu.com,
	ebiederm@...ssion.com, davem@...emloft.net, paul@...lmenage.org,
	gthelen@...gle.com, netdev@...r.kernel.org, linux-mm@...ck.org,
	kirill@...temov.name, avagin@...allels.com, devel@...nvz.org,
	eric.dumazet@...il.com, cgroups@...r.kernel.org
Subject: Re: [PATCH v6 01/10] Basic kernel memory functionality for the
 Memory Controller

On Fri, 25 Nov 2011 15:38:07 -0200
Glauber Costa <glommer@...allels.com> wrote:

> This patch lays down the foundation for the kernel memory component
> of the Memory Controller.
> 
> As of today, I am only laying down the following files:
> 
>  * memory.independent_kmem_limit
>  * memory.kmem.limit_in_bytes (currently ignored)
>  * memory.kmem.usage_in_bytes (always zero)
> 
> Signed-off-by: Glauber Costa <glommer@...allels.com>
> Reviewed-by: Kirill A. Shutemov <kirill@...temov.name>
> CC: Paul Menage <paul@...lmenage.org>
> CC: Greg Thelen <gthelen@...gle.com>
> ---
>  Documentation/cgroups/memory.txt |   36 ++++++++++++-
>  init/Kconfig                     |   14 +++++
>  mm/memcontrol.c                  |  107 ++++++++++++++++++++++++++++++++++++--
>  3 files changed, 150 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> index 06eb6d9..bf00cd2 100644
> --- a/Documentation/cgroups/memory.txt
> +++ b/Documentation/cgroups/memory.txt
> @@ -44,8 +44,9 @@ Features:
>   - oom-killer disable knob and oom-notifier
>   - Root cgroup has no limit controls.
>  
> - Kernel memory and Hugepages are not under control yet. We just manage
> - pages on LRU. To add more controls, we have to take care of performance.
> + Hugepages is not under control yet. We just manage pages on LRU. To add more
> + controls, we have to take care of performance. Kernel memory support is work
> + in progress, and the current version provides basically functionality.
>  
>  Brief summary of control files.
>  
> @@ -56,8 +57,11 @@ Brief summary of control files.
>  				 (See 5.5 for details)
>   memory.memsw.usage_in_bytes	 # show current res_counter usage for memory+Swap
>  				 (See 5.5 for details)
> + memory.kmem.usage_in_bytes	 # show current res_counter usage for kmem only.
> +				 (See 2.7 for details)
>   memory.limit_in_bytes		 # set/show limit of memory usage
>   memory.memsw.limit_in_bytes	 # set/show limit of memory+Swap usage
> + memory.kmem.limit_in_bytes	 # if allowed, set/show limit of kernel memory
>   memory.failcnt			 # show the number of memory usage hits limits
>   memory.memsw.failcnt		 # show the number of memory+Swap hits limits
>   memory.max_usage_in_bytes	 # show max memory usage recorded
> @@ -72,6 +76,9 @@ Brief summary of control files.
>   memory.oom_control		 # set/show oom controls.
>   memory.numa_stat		 # show the number of memory usage per numa node
>  
> + memory.independent_kmem_limit	 # select whether or not kernel memory limits are
> +				   independent of user limits
> +
>  1. History
>  
>  The memory controller has a long history. A request for comments for the memory
> @@ -255,6 +262,31 @@ When oom event notifier is registered, event will be delivered.
>    per-zone-per-cgroup LRU (cgroup's private LRU) is just guarded by
>    zone->lru_lock, it has no lock of its own.
>  
> +2.7 Kernel Memory Extension (CONFIG_CGROUP_MEM_RES_CTLR_KMEM)
> +
> + 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
> +possible to DoS the system by consuming too much of this precious resource.
> +Kernel memory limits are not imposed for the root cgroup.
> +
> +Memory limits as specified by the standard Memory Controller may or may not
> +take kernel memory into consideration. This is achieved through the file
> +memory.independent_kmem_limit. A Value different than 0 will allow for kernel
> +memory to be controlled separately.
> +
> +When kernel memory limits are not independent, the limit values set in
> +memory.kmem files are ignored.
> +
> +Currently no soft limit is implemented for kernel memory. It is future work
> +to trigger slab reclaim when those limits are reached.
> +
> +CAUTION: As of this writing, the kmem extention may prevent tasks from moving
> +among cgroups. If a task has kmem accounting in a cgroup, the task cannot be
> +moved until the kmem resource is released. Also, until the resource is fully
> +released, the cgroup cannot be destroyed. So, please consider your use cases
> +and set kmem extention config option carefully.
> +

This seems that memcg 'has' kernel memory limiting feature for all kinds of kmem..
Could you add a list of "currently controled kmems" section ?
And update the list in later patch ?

Thanks,
-Kame


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