As PTE-mapped large folios become more relevant (mTHP [1]) and there is
the desire to shrink the metadata allocated for such large folios as
well (memdesc [2]), how we track folio mappings gets more relevant. Over
the years, we used folio mapping information to answer various
questions: is this folio mapped by somebody else? do we have to COW on
write fault? how do we adjust memory statistics? ...
Let's talk about ongoing work in the mapcount area, get a common
understanding of what the users of the different mapcounts are and what
the implications of removing some would be: which questions could we
answer differently, which questions would we not be able to answer
precisely anymore, and what would be the implications of such changes?
For example, can we tolerate some imprecise memory statistics? How
expressive is the PSS when large folios are only partially mapped? Would
we need a transition period and glue changes to a new CONFIG_ option? Do
we really have to support THP and friends on 32bit?
[1]
https://patchwork.kernel.org/project/linux-mm/cover/20231207161211.2374093-1-ryan.roberts@xxxxxxx/#25628022
[2] https://kernelnewbies.org/MatthewWilcox/Memdescs
--
Cheers,
David / dhildenb
