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[[!tag open_issue_gnumach]]

IRC, freenode, #hurd, 2011-10:

    <braunr> antrik: about our physical memory limitations, i told you some
      time ago that part of it was due to the linux drivers
    <braunr> and i mentioned the paper concerning the integration of the linux
      drivers written at the time
    <braunr> it does indeed tell that mach, which used the common 3G->4G area
      for the kernel space had to be adapted
    <braunr> because linux used segmentation so that kernel addresses matched
      physical addresses
    <braunr> and it looks like some (many) drivers require that
    <braunr> our current gnumach actually does this (which i found surprising
      when i first found it)
    <braunr> and i believe the easy solution to exceed this limitation is to
      use a strategy similar to what linux still does on i386
    <braunr> some highmem support
    <braunr> we could alter the vm_resident module so that, by default, it
      still looks for pages in the low 0-800 (or 0-1800 on debian patched
      kernels) area
    <braunr> but for everything else than the kernel, e.g. all user processes
    <braunr> we could use a flag or a specialized function that would first
      look in the highmem pool for available physical pages to map
    <braunr> the only thing i'm not yet sure of is about user/kernel transfers
    <braunr> if virtual addresses and copies are always cleanly done, then it's
      ok
    <braunr> and i really hope our linux drivers do so :)
    <braunr> (i mean ,the glue code ofc)

2011-10-23:

    <youpi> braunr: I believe, like Linus, that highmem support is a nightmare
    <antrik> braunr: uhm... the drivers want virtual addressses to match
      physical ones? I guess that means switching address spaces before any
      driver code is executed?...