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    SubjectRe: Linux/IA-64 byte order
    Oliver Xymoron writes:
    > On Tue, 9 Mar 1999, Richard Gooch wrote:
    > > > Make an empty map for little-endian direct access and make a backing
    > > > map with the actual file. Then install a signal handler to catch
    > > > reads in the empty map, copy a page (or more) with byteswapping, and
    > > > you're done. "Loading" is still extremely fast.
    > >
    > > Yes, "loading" a subsection of the data is still (fairly) fast. But
    > > that doesn't solve the other problem: huge swap space consumption when
    > > you want to access the entire dataset. It's often the case that you
    > > have much more data disc than you have swap disc.
    > Does a method exist to mark the copied pages discardable so they
    > don't end up on swap? Obviously not a perfect solution, but not
    > bad.

    Not that I know of. BTW: I don't really see how your scheme would
    work, since I don't think you could "make an empty map" anyway. All
    you could do is find a vacant region in VM, and mmap() a single page
    at a time as you needed it. That's horrible.

    > > > As David Miller suggests, this might be a complete non-issue. We can
    > > > for instance speculate that the processor has a byteswap micro-op
    > > > that can be added to an instruction pipeline with little or no
    > > > cost. Or other such magic. Remember, we're talking about a fairly
    > > > novel architecture.
    > >
    > > Special BE load instructions are going to be messy to use, because you
    > > have to keep track of "where" the data came from (mmap() or malloc())
    > > all the way along.
    > >
    > > The possibility of tagging regions for BE access via the page tables
    > > looks good, though. Hopefully IA-64 will support it. And hopefully
    > > Linus accepts such an approach.
    > An alternate hack might be to push the on-the-fly-swap I suggested
    > down into the VM layer by having a flag somewhere in the mmap
    > API. This is cute, because then whether the swap were being done by
    > a bit in the page tables or by software, it could be portable to
    > other Linux platforms.

    You don't need to hack the VM layer to do this. You could probably
    implement it in a device driver which provided a mmap()able
    device. But the problem is you'd need root privileges to load the

    > Yes, I know it's sick. And I haven't even told you the really
    > disgusting part: the DSM folks will love it because it lets them
    > share memory between architectures! Don't choke, Larry!

    You have an evil sense of humour.



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