From: Yang Shi Subject: sched: coredump.h: clarify the use of MMF_VM_HUGEPAGE Patch series "Make khugepaged collapse readonly FS THP more consistent", v3. The readonly FS THP relies on khugepaged to collapse THP for suitable vmas. But it is kind of "random luck" for khugepaged to see the readonly FS vmas (see report: https://lore.kernel.org/linux-mm/00f195d4-d039-3cf2-d3a1-a2c88de397a0@suse.cz/) since currently the vmas are registered to khugepaged when: - Anon huge pmd page fault - VMA merge - MADV_HUGEPAGE - Shmem mmap If the above conditions are not met, even though khugepaged is enabled it won't see readonly FS vmas at all. MADV_HUGEPAGE could be specified explicitly to tell khugepaged to collapse this area, but when khugepaged mode is "always" it should scan suitable vmas as long as VM_NOHUGEPAGE is not set. So make sure readonly FS vmas are registered to khugepaged to make the behavior more consistent. Registering suitable vmas in common mmap path, that could cover both readonly FS vmas and shmem vmas, so removed the khugepaged calls in shmem.c. Patches 1 ~ 7 are minor bug fixes, clean up and preparation patches. Patch 8 is the real meat. Tested with khugepaged test in selftests and the testcase provided by Vlastimil Babka in https://lore.kernel.org/lkml/df3b5d1c-a36b-2c73-3e27-99e74983de3a@suse.cz/ by commenting out MADV_HUGEPAGE call. This patch (of 8): MMF_VM_HUGEPAGE is set as long as the mm is available for khugepaged by khugepaged_enter(), not only when VM_HUGEPAGE is set on vma. Correct the comment to avoid confusion. Link: https://lkml.kernel.org/r/20220404200250.321455-1-shy828301@gmail.com Link: https://lkml.kernel.org/r/20220404200250.321455-2-shy828301@gmail.com Signed-off-by: Yang Shi Reviewed-by: Miaohe Lin Acked-by: Song Liu Cc: Vlastimil Babka Cc: "Kirill A. Shutemov" Cc: Rik van Riel Cc: Matthew Wilcox Cc: Zi Yan Cc: Theodore Ts'o Signed-off-by: Andrew Morton --- include/linux/sched/coredump.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/include/linux/sched/coredump.h~sched-coredumph-clarify-the-use-of-mmf_vm_hugepage +++ a/include/linux/sched/coredump.h @@ -57,7 +57,8 @@ static inline int get_dumpable(struct mm #endif /* leave room for more dump flags */ #define MMF_VM_MERGEABLE 16 /* KSM may merge identical pages */ -#define MMF_VM_HUGEPAGE 17 /* set when VM_HUGEPAGE is set on vma */ +#define MMF_VM_HUGEPAGE 17 /* set when mm is available for + khugepaged */ /* * This one-shot flag is dropped due to necessity of changing exe once again * on NFS restore _