[mm-unstable v4 PATCH 0/8] Make khugepaged collapse readonly FS THP more consistent

[Yang Shi]

Changelog
v4: * Incorporated Vlastimil's comments for patch 6/8.
    * Reworked the commit log of patch 8/8 to make what the series fixed
      clearer.
    * Rebased onto mm-unstable tree.
    * Collected the acks from Vlastimil.
v3: * Register mm to khugepaged in common mmap path instead of touching
      filesystem code (patch 8/8).
    * New patch 7/8 cleaned up and renamed khugepaged_enter_vma_merge()
      to khugepaged_enter_vma().
    * Collected acked-by from Song Liu for patch 1 ~ 6.
    * Rebased on top of 5.18-rc1.
v2: * Collected reviewed-by tags from Miaohe Lin.
    * Fixed build error for patch 4/8.

The readonly FS THP relies on khugepaged to collapse THP for suitable
vmas.  But the behavior is inconsistent for "always" mode (https://lore.kernel.org/linux-mm/00f195d4-d039-3cf2-d3a1-a2c88de397a0@xxxxxxx/).

The "always" mode means THP allocation should be tried all the time and
khugepaged should try to collapse THP all the time. Of course the
allocation and collapse may fail due to other factors and conditions.

Currently file THP may not be collapsed by khugepaged even though all
the conditions are met. That does break the semantics of "always" mode.

So make sure readonly FS vmas are registered to khugepaged to fix the
break.

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.

The patch 1 ~ 7 are minor bug fixes, clean up and preparation patches.
The 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@xxxxxxx/
by commenting out MADV_HUGEPAGE call.


Yang Shi (8):
      sched: coredump.h: clarify the use of MMF_VM_HUGEPAGE
      mm: khugepaged: remove redundant check for VM_NO_KHUGEPAGED
      mm: khugepaged: skip DAX vma
      mm: thp: only regular file could be THP eligible
      mm: khugepaged: make khugepaged_enter() void function
      mm: khugepaged: make hugepage_vma_check() non-static
      mm: khugepaged: introduce khugepaged_enter_vma() helper
      mm: mmap: register suitable readonly file vmas for khugepaged

 include/linux/huge_mm.h        | 14 ++++++++++++++
 include/linux/khugepaged.h     | 44 ++++++++++++++++++--------------------------
 include/linux/sched/coredump.h |  3 ++-
 kernel/fork.c                  |  4 +---
 mm/huge_memory.c               | 15 ++++-----------
 mm/khugepaged.c                | 61 ++++++++++++++++++++++++++-----------------------------------
 mm/mmap.c                      | 18 ++++++++++++------
 mm/shmem.c                     | 12 ------------
 8 files changed, 77 insertions(+), 94 deletions(-)