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


    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
    +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
    + pages can be reclaimed
    +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
    + 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
    _
    --
    Warm Regards,
    Balbir Singh
    Linux Technology Center
    IBM, ISTL


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