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    SubjectRe: Ideas for memory management hackers (2)
    On 16 Nov 1997, Hans-Christoph Rohland wrote:
    > (I discussed some of these items with David Miller at Linux Kongress,
    > Germany. Dave you remember?)
    >
    > I think the virtual memory support in linux has the following
    > weaknesses irt. applications which use loads of virtual memory in
    > parallel processes:
    >
    > - Support for shared pages:
    > - No aging (?)
    fixed by my patch (vhand)

    > - VM areas are limited to 128MB. This leads to many swap-files. (I am
    > not quite shure about further limitation. Does it mean that bigger
    > mmaps are not possible? The swapfile limitation is definitely in the
    > kernel.)

    Are they???

    > 1) Good support for swapping of shared pages

    Aging is step 1, efficiency will have to be looked into...

    > 4) implementation of the 'madvise' call, especially the MADV_DONTNEED
    > parameter.

    This could be done by a simple syscall whereby a process sets
    the age of a specified (own) page to 0.

    > The need for MADV_DONTNEED is a similar problem: no memory manager can
    > know that I really don't need a part of memory any more. It will
    > always try to save the memory in backing store.
    > But especially transactional programs process some memory and when the
    > transaction finishes there is no need to get this content again. It
    > will be overwritten by the next transaction. So the program can
    > advise the OS to simply discard the page instead of saving the page to
    > the swapfile. This can increase the system performance a lot under low
    > physical memory.

    Ahh, I get it. Now, how should we implement this one?

    Rik.

    PLEASE, test my vhand patch and send comments/flames/code improvements
    to me...
    ----------
    Send Linux memory-management wishes to me: I'm currently looking
    for something to hack...


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