On 26/03/2024 17:04, David Hildenbrand wrote: >>>>> >>>>> Likely, we just want to read "the real deal" on both sides of the pte_same() >>>>> handling. >>>> >>>> Sorry I'm not sure I understand? You mean read the full pte including >>>> access/dirty? That's the same as dropping the patch, right? Of course if we do >>>> that, we still have to keep pte_get_lockless() around for this case. In an >>>> ideal >>>> world we would convert everything over to ptep_get_lockless_norecency() and >>>> delete ptep_get_lockless() to remove the ugliness from arm64. >>> >>> Yes, agreed. Patch #3 does not look too crazy and it wouldn't really affect any >>> architecture. >>> >>> I do wonder if pte_same_norecency() should be defined per architecture and the >>> default would be pte_same(). So we could avoid the mkold etc on all other >>> architectures. >> >> Wouldn't that break it's semantics? The "norecency" of >> ptep_get_lockless_norecency() means "recency information in the returned pte may >> be incorrect". But the "norecency" of pte_same_norecency() means "ignore the >> access and dirty bits when you do the comparison". > > My idea was that ptep_get_lockless_norecency() would return the actual result on > these architectures. So e.g., on x86, there would be no actual change in > generated code. I think this is a bad plan... You'll end up with subtle differences between architectures. > > But yes, the documentation of these functions would have to be improved. > > Now I wonder if ptep_get_lockless_norecency() should actively clear > dirty/accessed bits to more easily find any actual issues where the bits still > matter ... I did a version that took that approach. Decided it was not as good as this way though. Now for the life of me, I can't remember my reasoning. > >> >> I think you could only do the optimization you describe if you required that >> pte_same_norecency() would only be given values returned by >> ptep_get_lockless_norecency() (or ptep_get_norecency()). Even then, its not >> quite the same; if a page is accessed between gets one will return true and the >> other false. > > Right. >
