Re: 2G memory split

From: Dave Hansen
Date: Tue Jan 10 2006 - 13:53:53 EST


On Tue, 2006-01-10 at 10:34 -0800, Linus Torvalds wrote:
> On Tue, 10 Jan 2006, Martin Bligh wrote:
> >
> > The non-1GB-aligned ones need to be disbarred when PAE is on, I think.
>
> Well, right now _all_ the non-3:1 cases need to be disbarred. I think we
> depend on the kernel mapping only ever being the _one_ last entry in the
> top-level page table, which is only true with the 3:1 mapping.

It actually "just works". We have a 16GB machine that gets a lot of
filesystem activity and use a 2:2 split all the time. Appended patch is
all that we need.

It was for other reasons at the time, but I think we fixed a bunch of
the multiple kernel mapping PMDs back in 2.5. Some remnants of that
stuff are still around.

http://marc.theaimsgroup.com/?l=linux-kernel&m=104197008817507&w=2

diff -purN -X /home/dvhart/.diff.exclude /home/linux/views/linux-2.6.12/include/asm-i386/page.h 2.6.12-uptime/include/asm-i386/page.h
--- /home/linux/views/linux-2.6.12/include/asm-i386/page.h 2005-03-02 03:00:08.000000000 -0800
+++ 2.6.12-uptime/include/asm-i386/page.h 2005-07-27 11:53:40.000000000 -0700
@@ -122,9 +122,9 @@ extern int sysctl_legacy_va_layout;
#endif /* __ASSEMBLY__ */

#ifdef __ASSEMBLY__
-#define __PAGE_OFFSET (0xC0000000)
+#define __PAGE_OFFSET (0x80000000)
#else
-#define __PAGE_OFFSET (0xC0000000UL)
+#define __PAGE_OFFSET (0x80000000UL)
#endif

-- Dave

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