Re: [RFC][3/3] Update documentation for virtual address space control

[Randy Dunlap <randy.dunlap@oracle.com>]

On Sun, 16 Mar 2008 23:00:17 +0530 Balbir Singh wrote:

> This patch adds documentation for virtual address space control.
> 
> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
> 
>  Documentation/controllers/memory.txt |   26 +++++++++++++++++++++++++-
>  1 file changed, 25 insertions(+), 1 deletion(-)
> 
> diff -puN Documentation/controllers/memory.txt~memory-controller-virtual-address-control-documentation Documentation/controllers/memory.txt
> --- linux-2.6.25-rc5/Documentation/controllers/memory.txt~memory-controller-virtual-address-control-documentation	2008-03-16 22:57:44.000000000 +0530
> +++ linux-2.6.25-rc5-balbir/Documentation/controllers/memory.txt	2008-03-16 22:57:44.000000000 +0530
> @@ -237,7 +237,31 @@ cgroup might have some charge associated
>  tasks have migrated away from it. Such charges are automatically dropped at
>  rmdir() if there are no tasks.
>  
> -5. TODO
> +5. Virtual address space accounting
> +
> +A new resource counter controls the address space expansion of the tasks in
> +the cgroup. Address space control is provided along the same lines as
> +RLIMIT_AS control, which is available via getrlimit(2)/setrlimit(2).
> +The interface for controlling address space is provided through
> +"as_limit_in_bytes". The file is similar to "limit_in_bytes" w.r.t the user

                                                                w.r.t.
  or even spelled out.

> +interface. Please see section 3 for more details on how to use the user
> +interface to get and set values.
> +
> +The "as_usage_in_bytes" file provides information about the total address
> +space usage of the cgroup in bytes.
> +
> +5.1 Advantages of providing this feature
> +
> +1. Control over virtual address space allows for a cgroup to fail gracefully
> +   i.e, via a malloc or mmap failure as compared to OOM kill when no

      i.e.,

> +   pages can be reclaimed

end with period.

> +2. It provides better control over how many pages can be swapped out when
> +   the cgroup goes over it's limit. A badly setup cgroup can cause excessive

                           its (not "it is")

> +   swapping. Providing control over the address space allocations ensures
> +   that the system administrator has control over the total swapping that
> +   can take place.
> +
> +6. TODO
>  
>  1. Add support for accounting huge pages (as a separate controller)
>  2. Make per-cgroup scanner reclaim not-shared pages first
> _

---
~Randy

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