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Re: [Xen-devel] [PATCH] turn off writable page tables

On 29 Jul 2006, at 00:10, Zachary Amsden wrote:

For SMP, the enter / leave must happen under protection of the page table
locks for page tables which are being modified.

This should be in a comment in the code

Most definitely agreed! I think it deserves an entire paragraph explaining how to use it properly. But I wanted to get input from the Xen folks to see if this can be useful for them in some way first.

It would allow set_pte() to switch between explicit queuing and 'direct' writing. We moved away from the former a few years back as doing it everywhere made a mess of the generic Linux mm code and it was hard to reason whether our patches were correct. I guess doing it for the most important subset of mm routines is not so bad. It's a shame that, although many set_pte() call sites could determine statically whether or not they will batch, we'd end up with a dynamic run-time test everywhere (unless I'm mistaken) -- I wonder if that has a measurable cost?

 -- Keir

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