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