In article <local.mail.freebsd-hackers/[EMAIL PROTECTED]> you
write:
>Reading some documents and sources I came to the following conclusion:
>
>We support 4 Kbyte pages and 4 Mbyte pages, but we do not support 2
>Mbyte pages. On IA-32 at least.
>
>Is there a reason to?
>
>I could understand that some people would prefer 2 Mbyte pages in some
>situations. But looking at pmap.c I see we only test CPUID_PSE and
>don't use CPUID_PAE anywhere.
My initial feeling is that it wouldn't win us anything. We use a two-level
page table, with the first level covering a 4MB page, and the second level
containing 1024 pte's, each covering 4K.
Since each pte takes up 4 bytes, by using a 4MB page, we eliminate an
entire page of pte's at the second level. With a 2M page, we would still
need a second level page entry, plus some code to differentiate between
4K entries and a "half-page" 2M entry.
But I'm by no means a vm hacker, so I may be wrong here.
--
Jonathan
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