We have a 3x throughput improvement reported by Intel's kernel test
robot: https://lore.kernel.org/all/202404261055.c5e24608-oliver.sang@intel.com/

This is from delaying taking the mmap_lock for page faults until we
actually need the mmap_lock in order to assign an anon_vma to the vma.
It cleans up the page fault path a little by making the anon fault
handler more similar to the file fault handler.

Matthew Wilcox (Oracle) (4):
  mm: Assert the mmap_lock is held in __anon_vma_prepare()
  mm: Delay the check for a NULL anon_vma
  mm: Fix some minor per-VMA lock issues in userfaultfd
  mm: Optimise vmf_anon_prepare() for VMAs without an anon_vma

 mm/huge_memory.c |  6 ++++--
 mm/memory.c      | 42 +++++++++++++++++++++++++++---------------
 mm/rmap.c        |  3 +--
 mm/userfaultfd.c | 20 +++++++++-----------
 4 files changed, 41 insertions(+), 30 deletions(-)

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2.43.0