On 05/19/2017 09:31 AM, Zi Yan wrote:

quoted

This description lacks a problem statement.  What's the problem?

	_PAGE_PSE is used to distinguish between a truly non-present
	(_PAGE_PRESENT=0) PMD, and a PMD which is undergoing a THP
	split and should be treated as present.

	But _PAGE_SWP_SOFT_DIRTY currently uses the _PAGE_PSE bit,
	which would cause confusion between one of those PMDs
	undergoing a THP split, and a soft-dirty PMD.

	Thus, we need to move the bit.

Does that capture it?

Yes. I will add this in the next version.

OK, thanks for clarifying.  You can add my acked-by on this.

But, generally, these bits really scare me.  We don't have any nice
programmatic way to find conflicts.  I really wish we had some
BUILD_BUG_ON()s or something to express these dependencies.



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