HugeTLB pages may soon support being mapped with PTEs. To allow for this case, merge HugeTLB's mapcount scheme with THP's. The first patch of this series comes from the HugeTLB high-granularity mapping series[1], though with some updates, as the original version was buggy[2] and incomplete. I am sending this change as part of this smaller series in hopes that it can be more thoroughly scrutinized. I haven't run any THP performance tests with this series applied. HugeTLB pages don't currently support being mapped with `compound=false`, but this mapcount scheme will make collapsing compound=false mappings in HugeTLB pages quite slow. This can be optimized with future patches (likely by taking advantage of HugeTLB's alignment guarantees). Matthew Wilcox is working on a mapcounting scheme[3] that will avoid the use of each subpage's mapcount. If this series is applied, Matthew's new scheme will automatically apply to HugeTLB pages. [1]: https://lore.kernel.org/linux-mm/20230218002819.1486479-6-jthoughton@xxxxxxxxxx/ [2]: https://lore.kernel.org/linux-mm/CACw3F538H+bYcvSY-qG4-gmrgGPRBgTScDzrX9suLyp_q+v_bQ@xxxxxxxxxxxxxx/ [3]: https://lore.kernel.org/linux-mm/Y9Afwds%2FJl39UjEp@xxxxxxxxxxxxxxxxxxxx/ James Houghton (2): mm: rmap: make hugetlb pages participate in _nr_pages_mapped mm: rmap: increase COMPOUND_MAPPED to support 512G HugeTLB pages include/linux/mm.h | 7 +------ mm/hugetlb.c | 4 ++-- mm/internal.h | 9 ++++----- mm/migrate.c | 2 +- mm/rmap.c | 35 ++++++++++++++++++++--------------- 5 files changed, 28 insertions(+), 29 deletions(-) base-commit: 9caa15b8a49949342bdf495bd47660267a3bd371 -- 2.40.0.rc0.216.gc4246ad0f0-goog
