[PATCH v4 0/2] khugepaged: collapse pmd for pte-mapped THP

[Song Liu]

Changes v3 => v4:
1. Simplify locking for pte_mapped_thp (Oleg).
2. Improve checks for the page in collapse_pte_mapped_thp() (Oleg).
3. Move HPAGE_PMD_MASK to collapse_pte_mapped_thp() (kbuild test robot).

Changes v2 => v3:
1. Update vma/pmd check in collapse_pte_mapped_thp() (Oleg).
2. Add Acked-by from Kirill

Changes v1 => v2:
1. Call collapse_pte_mapped_thp() directly from uprobe_write_opcode();
2. Add VM_BUG_ON() for addr alignment in khugepaged_add_pte_mapped_thp()
   and collapse_pte_mapped_thp().

This set is the newer version of 5/6 and 6/6 of [1]. Newer version of
1-4 of the work [2] was recently picked by Andrew.

Patch 1 enables khugepaged to handle pte-mapped THP. These THPs are left
in such state when khugepaged failed to get exclusive lock of mmap_sem.

Patch 2 leverages work in 1 for uprobe on THP. After [2], uprobe only
splits the PMD. When the uprobe is disabled, we get pte-mapped THP.
After this set, these pte-mapped THP will be collapsed as pmd-mapped.

[1] https://lkml.org/lkml/2019/6/23/23
[2] https://www.spinics.net/lists/linux-mm/msg185889.html

Song Liu (2):
  khugepaged: enable collapse pmd for pte-mapped THP
  uprobe: collapse THP pmd after removing all uprobes

 include/linux/khugepaged.h |  12 ++++
 kernel/events/uprobes.c    |   9 +++
 mm/khugepaged.c            | 125 ++++++++++++++++++++++++++++++++++++-
 3 files changed, 145 insertions(+), 1 deletion(-)

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2.17.1