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@xxxxxxx/) 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 the vmas in mmap path seems more preferred from performance point of view since page fault path is definitely hot path. The patch 1 ~ 7 are minor bug fixes, clean up and preparation patches. The patch 8 converts ext4 and xfs. We may need convert more filesystems, but I'd like to hear some comments before doing that. Tested with khugepaged test in selftests and the testcase provided by Vlastimil Babka in https://lore.kernel.org/lkml/df3b5d1c-a36b-2c73-3e27-99e74983de3a@xxxxxxx/ by commenting out MADV_HUGEPAGE call. b/fs/ext4/file.c | 4 +++ b/fs/xfs/xfs_file.c | 4 +++ b/include/linux/huge_mm.h | 9 +++++++ b/include/linux/khugepaged.h | 69 +++++++++++++++++++++---------------------------------------- b/include/linux/sched/coredump.h | 3 +- b/kernel/fork.c | 4 --- b/mm/huge_memory.c | 15 +++---------- b/mm/khugepaged.c | 71 ++++++++++++++++++++++++++++++++++++++++++++------------------- b/mm/shmem.c | 14 +++--------- 9 files changed, 102 insertions(+), 91 deletions(-)
