Re: 4MB pages and framebuffer access, x11perf results, 2.1.125

Linus Torvalds (torvalds@transmeta.com)
Wed, 28 Oct 1998 19:03:16 -0800 (PST)


On Thu, 29 Oct 1998, MOLNAR Ingo wrote:
>
> the 4m issue is i think conceptually a granularity thing. Theres nothing
> wrong with unmapping the middle 4M of a 12M framebuffer mapping, no matter
> how rare it would be.

There _is_ something wrong with it - namely that the VM layer has to know
how. And I think that we don't really want that, because teaching the VM
layer how complicates it oevrmuch for little gain. The generated code was
fairly horrible when everything checked the 4M bit in the PMD (it's
actualy in the pgd, but I used the pmd macros to clean up the conceptual
idea).

This is pretty non-negotiable, especially if you ever expect to be able to
back-port any chages like this into 2.2.x.

Linus

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