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    SubjectRE: why swap at all?

    > Executables and shared libraries live in the filesystem
    > cache. Evicting those from memory - because swapping is
    > disabled and "the VM should remove something from cache
    > instead" - will feel exactly the same as swapping ...

    I totally agree, you can't get away from evicting pages from memory to disk
    if your doing file system I/O because you eventually fill up memory. Any
    additional file system I/O requires evictions, period.

    Trying to preference executables and shared libraries is difficult because
    they are backed by named files, hence they also pagecache. (kind of reminds
    me of that little white speck on chicken poop. If it came out of the
    chicken, it's chicken poop too :)

    But there is the case where massive amounts of file system I/O (consider
    several fibre cards connecting to SAN attached storage that saturates the
    centerplane on some insanely large system) will force pages from running
    executables to be evicted, only to be faulted back a few milliseconds later.
    It's this thrashing effect that a separation eliminates if you have the
    ability to distinguish between executables (not just files mapped in
    executable but actual running processes) and non-executable pages.

    Consider how silly it would be for a system running a single process that
    consumes only 100k that generates so much filesystem I/O that the process is
    constantly paged out. When it needs to wake up again, becomes runnable and
    the program counter starts to access pages within the process address space,
    it gets faulted back in.

    Lather, Rinse, Repeat ...


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