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    SubjectRe: New Feature Idea: Compress swap file
    MOLNAR Ingo <> wrote:
    > On 20 Feb 1998, Stefan Monnier wrote:
    > > The only way I can see to make it successful is:
    > > 1 - compress fast
    > > 2 - compress a lot
    > > 3 - beware of mapping between incore addresses and compressed addresses.
    > Linux does not swap 'incore' addresses, so 3) is a non-issue.

    I meant "virtual addresses" vs "location in compressed swap".
    Currently this info is kept IIRC in the pagetable and doesn't incur
    any fragmentation. With compression, this can get noticeably nastier.

    > > All in all, unrealizable within Unix, but probably doable in a
    > > (non-conservatively) GC'd world (since the GC already knows what is a
    > > pointer and what is not and is able to move objects at will). LISP
    > > machines, Smalltalk machines, or JavaOS would probably be good systems
    > > to try it on.
    > Maybe unrealizable within Unix and NT, but not within Linux ;)

    Moving objects is very hard to do if you want to allow C programs that
    do "strange" pointer casts (in other words, 99.99% of all C programs).
    I believe a Linux hack that would prevent Linux from providing full C
    support would be very unpopular.
    Also the description of what is a pointer and what is not has to be known
    by the swap/compress code which amounts to standardizing it: most GC'd
    languages use their very own scheme and even the debug info (which
    could be used for more traditional languages like Fortran/C/Pascal)
    is not well standardized.

    Maybe not unrealizable within Unix or Linux, but very hard to make it
    work transparently.


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