Re: Oops in __free_pages_ok (pre7-1) (Long) (backtrace)

[Linus Torvalds <torvalds@transmeta.com>]

Ok,
 there's a pre7-4 out there that does the swapout with the page locked.
I've given it some rudimentary testing, but certainly nothing really
exotic. Please comment..

David pointed out that swapout_highmem can't really work, and he's right
and wrong. It does work, but it works for rather undocumented reasons: it
only gets invoced for anonymous dirty pages, and they are always
cow-shared, so it's ok to "break" the page up into an "old" page and a
"new" page with the same contents. Even though it's not legal in general.

I'm not claiming that this fixes any known bugs, but it _does_ mean that
we probably have the page locked in all fundamental cases where it really
matters. If anybody finds a case where we play with the page-cached-ness
(or similar) of a page without holding the page lock, please holler
loudly.

This way it should be easy to verify that yes, our coherency is fine.

		Linus

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