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    SubjectRe: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)
    On Wed, Mar 07, 2007 at 10:49:47AM +0100, Nick Piggin wrote:
    > On Wed, Mar 07, 2007 at 01:44:20AM -0800, Bill Irwin wrote:
    > > On Wed, Mar 07, 2007 at 10:28:21AM +0100, Nick Piggin wrote:
    > > > Depending on whether anyone wants it, and what features they want, we
    > > > could emulate the old syscall, and make a new restricted one which is
    > > > much less intrusive.
    > > > For example, if we can operate only on MAP_ANONYMOUS memory and specify
    > > > that nonlinear mappings effectively mlock the pages, then we can get
    > > > rid of all the objrmap and unmap_mapping_range handling, forget about
    > > > the writeout and msync problems...
    > >
    > > Anonymous-only would make it a doorstop for Oracle, since its entire
    > > motive for using it is to window into objects larger than user virtual
    >
    > Uh, duh yes I don't mean MAP_ANONYMOUS, I was just thinking of the shmem
    > inode that sits behind MAP_ANONYMOUS|MAP_SHARED. Of course if you don't
    > have a file descriptor to get a pgoff, then remap_file_pages is a doorstop
    > for everyone ;)
    >
    > > address spaces (this likely also applies to UML, though they should
    > > really chime in to confirm). Restrictions to tmpfs and/or ramfs would
    > > likely be liveable, though I suspect some things might want to do it to
    > > shm segments (I'll ask about that one). There's definitely no need for a
    > > persistent backing store for the object to be remapped in Oracle's case,
    > > in any event. It's largely the in-core destination and source of IO, not
    > > something saved on-disk itself.
    >
    > Yeah, tmpfs/shm segs are what I was thinking about. If UML can live with
    > that as well, then I think it might be a good option.

    Oh, hmm.... if you can truncate these things then you still need to
    force unmap so you still need i_mmap_nonlinear.

    But come to think of it, I still don't think nonlinear mappings are
    too bad as they are ;)
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