[PATCH 0/5] madvise cleanup

[Lorenzo Stoakes]

This is a series of patches that helps address a number of historic
problems in the madvise() implementation:

* Eliminate the visitor pattern and having the code which is implemented
  for both the anon_vma_name implementation and ordinary madvise()
  operations use the same madvise_vma_behavior() implementation.

* Thread state through the madvise_behavior state object - this object,
  very usefully introduced by SJ, is already used to transmit state through
  operations. This series extends this by having all madvise() operations
  use this, including anon_vma_name.

* Thread range, VMA state through madvise_behavior - This helps avoid a lot
  of the confusing code around range and VMA state and again keeps things
  consistent and with a single 'source of truth'.

* Addressing the very strange behaviour around the passed around struct
  vm_area_struct **prev pointer - all read-only users do absolutely nothing
  with the prev pointer. The only function that uses it is
  madvise_update_vma(), and in all cases prev is always reset to
  VMA.

  Fix this by no longer having aything but madvise_update_vma() reference
  prev, and having madvise_walk_vmas() update prev in each
  instance. Additionally make it clear that the meaningful change in vma
  state is when madvise_update_vma() potentially merges a VMA, so
  explicitly retrieve the VMA in this case.

* Update and clarify the madvise_walk_vmas() function - this is a source of
  a great deal of confusion, so simplify, stop using prev = NULL to signify
  that the mmap lock has been dropped (!) and make that explicit, and add
  some comments to explain what's going on.

Lorenzo Stoakes (5):
  mm/madvise: remove the visitor pattern and thread anon_vma state
  mm/madvise: thread mm_struct through madvise_behavior
  mm/madvise: thread VMA range state through madvise_behavior
  mm/madvise: thread all madvise state through madv_behavior
  mm/madvise: eliminate very confusing manipulation of prev VMA

 include/linux/huge_mm.h |   9 +-
 mm/khugepaged.c         |   9 +-
 mm/madvise.c            | 569 +++++++++++++++++++++-------------------
 3 files changed, 309 insertions(+), 278 deletions(-)

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2.49.0