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    SubjectRe: swap cache
    Date
    > 
    > On Sat, 19 Dec 1998, Prasun Kapoor wrote:
    >
    > > > Linux VM, but we don't need that functionality: in Linux we have always
    > > > swapped out ptes on a per-page-table basis, not on a per-physical-page
    > > > basis. We *DO* swap processes out independently.
    > >
    > > I dont think I understand. The whole idea of doing it globally is
    > > to do some kind of LRU on a global scale and swap out pages based
    > > on that.
    >
    > This terribly fragments swap space -- you seem to be forgetting
    > that we also need to swap things back _in_ and that is most
    > efficient when the process' pages are contiguous on disk.
    >
    > LRU is just a good guess, the method Linux uses might be a bit
    > worse on swap-out, but since we do less disk _seek_ I/O we come
    > out slightly ahead of the normal way...
    >
    > For Linux 2.3 we are planning several major enhancements to
    > this scheme though (much better I/O clustering and swap read-
    > ahead/behind and several other goodies).

    read ahead/behind i assume refers to clustering for I/O.

    Also i was thinking about one of the other suggestions that was made regarding
    the compression of a page(s) to a portion of the RAM, and uncompress it as part
    of the swap back in. Although the compression/un-compression has to be measured
    against the I/O cost. This will also involve looking at the available RAM. On a
    small system with less RAM, this may not be a wise-thing to do.

    It would be intersting to know if any1 has implemented such a thing and what's
    the cost involved vis-a-vis available RAM, i/o etc.

    thanks,
    Rama.

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