Re: PAE and PSE ??

["H. Peter Anvin" <hpa@zytor.com>]

Rafael J. Wysocki wrote:
> Hi,
>
> On Sunday, 22 October 2006 08:29, Sandeep Kumar wrote:
> > Hi all,
> > I have read in UTLK by bovet that the linux kernel does not uses the
> > PSE bit on an x86
> > machine. Then how come we have the hugetlbfs, which provides support
> > for 4MB pages ?
>
> AFAIK, PSE is only used when PAE is not set and then it enables the 4 MB
> pages.  If PAE is set, the 4 MB pages are impossible because there are only
> 512 entries per page table, but 2 MB pages can be used instead (and you don't
> need to set PSE to use them).

You're wrong.

PSE refers to 4 MB pages when PAE is not used, and 2 MB pages when PAE 
is used.

In theory, you could have PAE without PSE, which would only support 4K 
pages.

Linux uses PSE; it may or may not use PAE depending on the configuration.

	-hpa
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