On Monday 23 January 2006 18:19, Dave McCracken wrote:
<snip>

The basic rule for pte sharing is that some portion of a memory region must
span an entire pte page.  For i386 and x96_64 that would be 2 meg.  The
region must either be read-only or marked to be shared if it is writeable.

Yeah, I figured that out just after hitting "send" on that first note.  :-(

The code does opportunistically look for any pte page that is fully within
a shareable vma, and will share if it finds one.

Oh, and one more caveat.  The region must be mapped to the same address in
each process.

quoted

I turned on the PT_DEBUG stuff, but thus far have found no evidence of
pte  sharing actually occurring in a normal system boot.  I'm surprised
by that as  I (naively?) would have expected shared libraries to use
shared ptes.

OK, with those guidelines I can put together a test program pretty quickly.
If you have one handy that would be fine, but don't put a lot of effort into 
it.

Thanks,

Most system software, including the shared libraries, don't have any
regions that are big enough for sharing (the text section for libc, for
example, is about 1.5 meg).

Ah, that explains that then.

Dave McCracken

-- 
Ray Bryant
AMD Performance Labs                   Austin, Tx
512-602-0038 (o)                 512-507-7807 (c)

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