[PATCH v2 0/4] further cleanup of vma_merge()

[Lorenzo Stoakes <lstoakes@gmail.com>]

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 - and to Liam for his excellent suggestions which greatly
simplified things.

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.

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

Lorenzo Stoakes (4):
  mm/mmap/vma_merge: further improve prev/next VMA naming
  mm/mmap/vma_merge: set next to NULL if not applicable
  mm/mmap/vma_merge: extend invariants, avoid invalid res, vma
  mm/mmap/vma_merge: init cleanup, be explicit about the non-mergeable
    case

 mm/mmap.c | 155 ++++++++++++++++++++++++++++--------------------------
 1 file changed, 80 insertions(+), 75 deletions(-)

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2.39.2