Currently, folio_referenced_one() always checks the young flag for each PTE
sequentially, which is inefficient for large folios. This inefficiency is
especially noticeable when reclaiming clean file-backed large folios, where
folio_referenced() is observed as a significant performance hotspot.

Moreover, on Arm architecture, which supports contiguous PTEs, there is already
an optimization to clear the young flags for PTEs within a contiguous range.
However, this is not sufficient. We can extend this to perform batched operations
for the entire large folio (which might exceed the contiguous range: CONT_PTE_SIZE).

Similar to folio_referenced_one(), we can also apply batched unmapping for large
file folios to optimize the performance of file folio reclamation. By supporting
batched checking of the young flags, flushing TLB entries, and unmapping, I can
observed a significant performance improvements in my performance tests for file
folios reclamation. Please check the performance data in the commit message of
each patch.

Run stress-ng and mm selftests, no issues were found.

Changes from v1:
 - Add a new patch to support batched unmapping for file large folios.
 - Update the cover letter.

Baolin Wang (3):
  arm64: mm: support batch clearing of the young flag for large folios
  mm: rmap: support batched checks of the references for large folios
  mm: rmap: support batched unmapping for file large folios

 arch/arm64/include/asm/pgtable.h | 23 ++++++++++++-----
 arch/arm64/mm/contpte.c          | 44 ++++++++++++++++++++++----------
 include/linux/mmu_notifier.h     |  9 ++++---
 include/linux/pgtable.h          | 19 ++++++++++++++
 mm/rmap.c                        | 29 +++++++++++++++++----
 5 files changed, 96 insertions(+), 28 deletions(-)

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2.47.3