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SubjectRe: [patch] jiffies wraparound [Re: 2.1.125 Show stopper list: Draft]

On Tue, 27 Oct 1998, Linus Torvalds wrote:

> > But it would be a neat feature nevertheless, unfortunately exporting 4MB
> > pages to ring 3 user-space doesnt seem to work (i've tried), only ring 0
> > is supposed to see those mappings.
>
> The VM layer currently gets confused if it sees a 4MB page.
>
> I actually had 4MB pages working at one point (with magic hackery to the
> pmd_xxx macros - no generic VM changes necessary), but it became fairly
> ugly, and the generated code was nasty for the normal case of 4kB pages.

my hack did it independently of the VM layer: fixing up the page table
directly when /dev/mem gets mapped in a magic way. (this is unsafe but i
just wanted to have a prototype first) I have tried really hard and others
have told me it's the right conclusion, but i'll try it again. It would be
a neat feature for XFree86 because it still happens quite often that the X
server touches the framebuffer: line endings are sometimes nonstandard and
have to be fixed up after an accel-line and small lines are faster in the
framebuffer than setting up a whole accelerated operation. Plus font
rendering is often done in the framebuffer too.

-- mingo


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