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    SubjectRe: [RFC][PATCH 1/4] Memory controller soft limit documentation
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    On Wed, Jan 7, 2009 at 10:41 AM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
    > -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 (through do_try_to_free_pages(),
    > +while allocating), control groups are pushed back to their soft limits if
    > +possible. 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.

    Can you give an example here of how to implement the following setup:

    - we have a high-priority latency-sensitive server job A and a bunch
    of low-priority batch jobs B, C and D

    - each job *may* need up to 2GB of memory, but generally each tends to
    use <1GB of memory

    - we want to run all four jobs on a 4GB machine

    - we don't want A to ever have to wait for memory to be reclaimed (as
    it's serving latency-sensitive queries), so the kernel should be
    squashing B/C/D down *before* memory actually runs out.

    Is this possible with the proposed hard/soft limit setup? Or do we
    need some additional support for keeping a pool of pre-reserved free
    memory available?

    Paul


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