linux-kernel - Re: [PATCH v4 1/8] Basic kernel memory functionality for the Memory Controller

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Message-Id: <20111004093851.7536e505.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 4 Oct 2011 09:38:51 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, paul@...lmenage.org,
	lizf@...fujitsu.com, ebiederm@...ssion.com, davem@...emloft.net,
	gthelen@...gle.com, netdev@...r.kernel.org, linux-mm@...ck.org,
	kirill@...temov.name, avagin@...allels.com
Subject: Re: [PATCH v4 1/8] Basic kernel memory functionality for the Memory
 Controller

On Mon,  3 Oct 2011 14:18:36 +0400
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>
> CC: Paul Menage <paul@...lmenage.org>
> CC: Greg Thelen <gthelen@...gle.com>
> ---
>  Documentation/cgroups/memory.txt |   30 +++++++++++-
>  init/Kconfig                     |   11 ++++
>  mm/memcontrol.c                  |   94 +++++++++++++++++++++++++++++++++++---
>  3 files changed, 126 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> index 6f3c598..6f1954a 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 +262,25 @@ 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.
> +

Please add some CAUTION like
==
"CAUTION: the kmem extetion prevents 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. And more, until the resource is
 fully released, the cgroup cannot be destroyed. So, please consider 
 your use cases and set kmem extention config carefully".
==

And add some memo to KCONFIG. This should be warned.

> +config CGROUP_MEM_RES_CTLR_KMEM
> +	bool "Memory Resource Controller Kernel Memory accounting (EXPERIMENTAL)"
> +	depends on CGROUP_MEM_RES_CTLR && EXPERIMENTAL
> +	default y

default must be n until you fixes the bug.


Thanks,
-Kame









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