Re: [RFC][PATCH 1/5] Memory controller soft limit documentation (v8)

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Thu, 09 Jul 2009 22:44:49 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> Feature: Add documentation for soft limits
> 
> From: Balbir Singh <balbir@linux.vnet.ibm.com>
> 
> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
> 
>  Documentation/cgroups/memory.txt |   31 ++++++++++++++++++++++++++++++-
>  1 files changed, 30 insertions(+), 1 deletions(-)
> 
> 
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> index ab0a021..b47815c 100644
> --- a/Documentation/cgroups/memory.txt
> +++ b/Documentation/cgroups/memory.txt
> @@ -379,7 +379,36 @@ cgroups created below it.
>  
>  NOTE2: This feature can be enabled/disabled per subtree.
>  
> -7. TODO
> +7. Soft limits
> +
> +Soft limits allow for greater sharing of memory. The idea behind soft limits
> +is to allow control groups to use as much of the memory as needed, provided
> +
> +a. There is no memory contention
> +b. They do not exceed their hard limit
> +
> +When the system detects memory contention or low memory control groups
> +are pushed back to their soft limits. If the soft limit of each control
> +group is very high, they are pushed back as much as possible to make
> +sure that one control group does not starve the others of memory.
> +

It's better to write "this is best-effort service". We add hook only to kswapd.
And hou successfull this work depends on ZONE.

Thanks,
-Kame

> +7.1 Interface
> +
> +Soft limits can be setup by using the following commands (in this example we
> +assume a soft limit of 256 megabytes)
> +
> +# echo 256M > memory.soft_limit_in_bytes
> +
> +If we want to change this to 1G, we can at any time use
> +
> +# echo 1G > memory.soft_limit_in_bytes
> +
> +NOTE1: Soft limits take effect over a long period of time, since they involve
> +       reclaiming memory for balancing between memory cgroups
> +NOTE2: It is recommended to set the soft limit always below the hard limit,
> +       otherwise the hard limit will take precedence.
> +
> +8. TODO
>  
>  1. Add support for accounting huge pages (as a separate controller)
>  2. Make per-cgroup scanner reclaim not-shared pages first
> 
> -- 
> 	Balbir
> 
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