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    SubjectRe: [patch 2.6.13-rc6] docs: fix misinformation about overcommit_memory
    On Fri, 19 Aug 2005 20:24:26 -0700, Andrew Morton wrote:

    > Chuck Ebbert <76306.1226@compuserve.com> wrote:
    > >
    > > +Controls overcommit of system memory:
    >
    > It should explain what "overcommit" is.


    Here is an improved version.

    Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>

    Documentation/filesystems/proc.txt | 42 ++++++++++++++++++++++++++++---------
    1 files changed, 32 insertions(+), 10 deletions(-)

    --- 2.6.13-rc6c.orig/Documentation/filesystems/proc.txt
    +++ 2.6.13-rc6c/Documentation/filesystems/proc.txt
    @@ -1240,16 +1240,38 @@ swap-intensive.
    overcommit_memory
    -----------------

    -This file contains one value. The following algorithm is used to decide if
    -there's enough memory: if the value of overcommit_memory is positive, then
    -there's always enough memory. This is a useful feature, since programs often
    -malloc() huge amounts of memory 'just in case', while they only use a small
    -part of it. Leaving this value at 0 will lead to the failure of such a huge
    -malloc(), when in fact the system has enough memory for the program to run.
    -
    -On the other hand, enabling this feature can cause you to run out of memory
    -and thrash the system to death, so large and/or important servers will want to
    -set this value to 0.
    +Controls overcommit of system memory, possibly allowing processes
    +to allocate (but not use) more memory than is actually available.
    +
    +
    +0 - Heuristic overcommit handling. Obvious overcommits of
    + address space are refused. Used for a typical system. It
    + ensures a seriously wild allocation fails while allowing
    + overcommit to reduce swap usage. root is allowed to
    + allocate slighly more memory in this mode. This is the
    + default.
    +
    +1 - Always overcommit. Appropriate for some scientific
    + applications.
    +
    +2 - Don't overcommit. The total address space commit
    + for the system is not permitted to exceed swap plus a
    + configurable percentage (default is 50) of physical RAM.
    + Depending on the percentage you use, in most situations
    + this means a process will not be killed while attempting
    + to use already-allocated memory but will receive errors
    + on memory allocation as appropriate.
    +
    +overcommit_ratio
    +----------------
    +
    +Percentage of physical memory size to include in overcommit calculations
    +(see above.)
    +
    +Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100)
    +
    + swapspace = total size of all swap areas
    + physmem = size of physical memory in system

    nr_hugepages and hugetlb_shm_group
    ----------------------------------
    __
    Chuck
    -
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