>Say i have 12Mb RAM. So that's 3 4Mb pages. When I need an uncached
>page, I'd map it into the 64M-68M range, mark that range as uncached,
And you'll lose 4mbyte of virtual addresses. We are very strict in the
4giga of virtual address space and we must be careful to not waste it.
To access a piece of memory with a uncached-pte you can use a
kmap_uncached() that maybe a variant of a plain kmap(). kmap() will avoid
you to waste lots virtual address space by using the per-CPU virtual
addresses allocated in the fixmap area. You'll have only to run an invlpg
before accessing the data (after updating the pte). See the bigmem patch
for more details.
Andrea
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