Messages in this thread | | | Date | Wed, 20 Mar 2002 21:17:31 +0000 (GMT) | From | Hugh Dickins <> | Subject | Re: Creating a per-task kernel space for kmap, user pagetables, et al |
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On Wed, 20 Mar 2002, Christoph Hellwig wrote: > On Wed, Mar 20, 2002 at 09:23:41PM +0100, Andrea Arcangeli wrote: > > we need to walk pagetables not just from the current task and mapping > > pagetables there would decrase the user address space too much. > > Who sais it should be taken from user address space? > For example openunix takes a small (I think 4MB) part of the normal KVA > to be per-process mapped.
Linux would want it to come from the user address space because it has no precedent for per-process addressing in the kernel address space, and much simpler to keep it that way.
> > I think you're missing the problem with mainline. There is no shortage > > of virtual address space, there is a shortage of physical ram in the > > zone normal. So we cannot keep them in zone normal (and there's no such > > thing as "mapping in zone_normal"). Maybe I misunderstood what you were > > saying. > > The problem is not the 4GB ZONE_NORMAL but the ~1GB KVA space. > UnixWare/OpenUnix had huge problems getting all kernel structs for managing > 16GB virtual into that - on the other hand their struct page is more > then twice as big as ours..
Which is more good reason to put user-address-space-specific-mappings (page table mappings; the filepage mapping case is less obvious) in the user address space (but of course not accessible to the user) - probably above user stack, since that's already of indefinite size.
Hugh
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