struct pst_static: physical_memory and pst_maxmem - HP UX

This is a discussion on struct pst_static: physical_memory and pst_maxmem - HP UX ; struct pst_static contains various members including: physical_memory; /* system physical memory in 4K pages */ pst_maxmem; /* actual max memory per process */ Is pst_maxmem only physical memory? What does pst_maxmem depend on? What is connection between physical_memory and pst_maxmem? ...

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Thread: struct pst_static: physical_memory and pst_maxmem

  1. struct pst_static: physical_memory and pst_maxmem

    struct pst_static contains various members including:

    physical_memory; /* system physical memory in 4K pages */
    pst_maxmem; /* actual max memory per process */

    Is pst_maxmem only physical memory?
    What does pst_maxmem depend on?
    What is connection between physical_memory and pst_maxmem?

    Alex Vinokur
    email: alex DOT vinokur AT gmail DOT com
    http://mathforum.org/library/view/10978.html
    http://sourceforge.net/users/alexvn

  2. Re: struct pst_static: physical_memory and pst_maxmem

    Alex Vinokur wrote:
    > struct pst_static contains various members including:
    >
    > physical_memory; /* system physical memory in 4K pages */
    > pst_maxmem; /* actual max memory per process */
    >
    > Is pst_maxmem only physical memory?


    Yes, it is the maximum physical memory any given user process
    could acquire (obviously assuming it manages to get every page
    away from any other user process -- in practical terms, you'd
    have to be extremely lucky [and at least RealTime priority]
    to ever manage this... but it is a high water mark to compare
    actual Resident Set Size consumption with as a proportion of
    User physical sizing).

    > What does pst_maxmem depend on?


    The amount of memory used by the kernel at boot for allocations
    which are pretty much never freed back to the system (and as
    such are considered unallocatable for users), some memory
    reserved for kernel critical allocation pools, and possibly
    partitioned user memory groups if you have the PRM product.

    Or in simple terms -- pst_maxmem = physical_memory - KernelFixedCosts

    Kernel dynamic memory fluctuates and as such isn't reflected
    dynamically via the pst_maxmem field [for one thing, if the
    system can flush out cached but free kernel memory that memory
    becomes usable again for user space].

    > What is connection between physical_memory and pst_maxmem?


    pst_maxmem is always strictly less than physical_memory.
    (You can never get more physical memory to a user process
    than the system has in total, and in practice the kernel
    will always consume some of it before users can).

    Don
    --
    kernel, n:
    A part of an operating system that preserves the medieval traditions
    of sorcery and black art.

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