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    Subject[-mm][PATCH 1/4] Add memrlimit controller documentation (v4)


    Documentation patch - describes the goals and usage of the memrlimit
    controller.


    Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
    ---

    Documentation/controllers/memrlimit.txt | 29 +++++++++++++++++++++++++++++
    1 file changed, 29 insertions(+)

    diff -puN /dev/null Documentation/controllers/memrlimit.txt
    --- /dev/null 2008-05-14 04:27:30.032276540 +0530
    +++ linux-2.6.26-rc2-balbir/Documentation/controllers/memrlimit.txt 2008-05-14 18:35:55.000000000 +0530
    @@ -0,0 +1,29 @@
    +This controller is enabled by the CONFIG_CGROUP_MEMRLIMIT_CTLR option. Prior
    +to reading this documentation please read Documentation/cgroups.txt and
    +Documentation/controllers/memory.txt. Several of the principles of this
    +controller are similar to the memory resource controller.
    +
    +This controller framework is designed to be extensible to control any
    +memory resource limit with little effort.
    +
    +This new controller, controls the address space expansion of the tasks
    +belonging to a 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
    +"rlimit.limit_in_bytes". The file is similar to "limit_in_bytes" w.r.t. the user
    +interface. Please see section 3 of the memory resource controller documentation
    +for more details on how to use the user interface to get and set values.
    +
    +The "memrlimit.usage_in_bytes" file provides information about the total address
    +space usage of the tasks in the cgroup, in bytes.
    +
    +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 its 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.
    _
    --
    Warm Regards,
    Balbir Singh
    Linux Technology Center
    IBM, ISTL


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