[PATCH v4 0/4] further cleanup of vma_merge()

[Lorenzo Stoakes]

Following on from Vlastimil Babka's patch series "cleanup vma_merge() and
improve mergeability tests" which was in turn based on Liam's prior
cleanups, this patch series introduces changes discussed in review of
Vlastimil's series and goes further in attempting to make the logic as
clear as possible.

Nearly all of this should have absolutely no functional impact, however it
does add a singular VM_WARN_ON() case.

With many thanks to Vernon for helping kick start the discussion around
simplification - abstract use of vma did indeed turn out not to be
necessary, Liam for his excellent suggestions which greatly simplified
things, and Vlastimil for his careful review and feedback.

v4:
- Mention 'A' -> '*' in commit message.
- Various small nits.

v3:
- Combine vma_lookup() cases and reinsert accidentally excluded next = NULL
  assignment.
- Reword commit messages to more correctly reflect the current changes.
- Avoid multiple assignment to prev, take vma_start, vma_pgoff assignment
  out of the local variable declarations and revert to setting in if (prev)
  block.
https://lore.kernel.org/all/cover.1679468982.git.lstoakes@xxxxxxxxx

v2:
- Put the patch series on a serious diet, cut comments down to avoid
  bloat.
- Added clever use of find_vma_intersection() and vma_lookup() as suggested
  by Liam which improved clarity + brevity significantly.
- Eliminated the use of a temporary vma local as suggested by Vernon, it
  does seem this was ultimately adding confusion and Liam's suggestions
  eliminated the need for this.
- Moved around initial variables to be more sensible and to initialise each
  variable in one place where possible.
https://lore.kernel.org/all/cover.1679431180.git.lstoakes@xxxxxxxxx

v1:
https://lore.kernel.org/all/cover.1679137163.git.lstoakes@xxxxxxxxx

Lorenzo Stoakes (4):
  mm/mmap/vma_merge: further improve prev/next VMA naming
  mm/mmap/vma_merge: fold curr, next assignment logic
  mm/mmap/vma_merge: explicitly assign res, vma, extend invariants
  mm/mmap/vma_merge: init cleanup, be explicit about the non-mergeable
    case

 mm/mmap.c | 138 ++++++++++++++++++++++++++++--------------------------
 1 file changed, 71 insertions(+), 67 deletions(-)

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2.39.2