Zero Pages / Cache Coherency

[Michel Lanners]

On  27 Aug, this message from Adrian Cox echoed through cyberspace:
> 
> I'm currently trying out the pre-zeroing of pages in the idle task, and
> I'm a little worried about its effect on cache-coherency. I can't prove
> to
> my satisfaction that none of the pages being cleared by zero_paged() is
> in the cache, and I'm not sure that turning off caching in the PTE will
> have any effect on cache lines already allocated in L1 or L2.

Cort Dougan had a paper about memory management in Linux on the PowerPC
online at NMT, but at this time the link is broken
(http://www.cs.nmt.edu/~cort/papers/linuxppc-mm/). If I remeber right,
he also spoke about zeroing pegaes in the idle task.

Cort, are you among us? What's up with your personal pages?

> Obviously, any incoherency would be extremely rare, but ensuring that
> the page is invalidated from the caches before it is zeroed has the
> added bonus of removing the need for a flush_page_to_ram() in my
> modified anonymous memory allocator.

I can't remeber whether Cort also treated this subject.

Michel

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