Re: ioremap()/PCI sickness in 2.4.18-rc2 (FIXED ALMOST)

Jeff V. Merkey
2002-02-20T23:19:15Z

On Wed, Feb 20, 2002 at 11:06:17PM +0000, Alan Cox wrote:
> > Sigh .... I am only using 2 GB on a 4GB capable processor (actually
> > a 64 GB capable processor). Looks like a patch is needed. Who is
> > maintaining vmalloc.c at present so I know who to submit a patch
> > to?
>
> Actually you are using a 64Gb capable processor that is only capable of
> sanely addressing 4Gb at a time, total across both user and kernel space
> and takes a hefty hit whenever you switch which 4Gb you are peering at.
>
> If you want to make sensible use of even 4Gb user/4Gb kernel you need to
> take a page table reload at syscall time and deal with quite messy handling
> for copy to/from user.
>
> [If someone from Intel disagrees please do so publically - I'd love to have
> someone prove the limit can be dealt with 8)]

I'll get to work on it. The 4 bit PTE extention to enable 48 bit
addresses is quite ugly, and I agree -- heavy. There may. however,
be no other way to make this work properly. The SCI address space is
explicitly addressable, so it may be possible to enable this on
the PCI-SCI adapters **ONLY** (not ccNuma) without getting into
general user/kernel copy issues since the SCI address space is
typically assumed in this model to be an explicit entity for most
apps. :-)

Jeff

Jeff

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