[PATCH v3 0/7] enable PT_RECLAIM on all 64-bit architectures

[Qi Zheng]

From: Qi Zheng <zhengqi.arch at bytedance.com>

Changes in v3:
 - modify the commit message in [PATCH v3 1/7] (suggested by David Hildenbrand)
 - make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE instead of 64BIT
 - collect Acked-by
 - rebase onto the next-20251217

Changelog in v2:
 - fix compilation errors (reported by Magnus Lindholm and kernel test robot)
 - adjust some code style (suggested by Huacai Chen)
 - make PT_RECLAIM user-unselectable (suggested by David Hildenbrand)
 - rebase onto the next-20251119

Hi all,

This series aims to enable PT_RECLAIM on all 64-bit architectures.

On a 64-bit system, madvise(MADV_DONTNEED) may cause a large number of empty PTE
page table pages (such as 100GB+). To resolve this problem, we need to enable
PT_RECLAIM, which depends on MMU_GATHER_RCU_TABLE_FREE.

Therefore, this series first enables MMU_GATHER_RCU_TABLE_FREE on all 64-bit
architectures, and finally makes PT_RECLAIM depend on MMU_GATHER_RCU_TABLE_FREE.
This way, PT_RECLAIM can be enabled by default on all 64-bit architectures.

Of course, this will also be enabled on some 32-bit architectures that already
support MMU_GATHER_RCU_TABLE_FREE. That's fine, PT_RECLAIM works well on all
32-bit architectures as well. Although the benefit isn't significant, there's
still memory that can be reclaimed. Perhaps PT_RECLAIM can be enabled on all
32-bit architectures in the future.

Comments and suggestions are welcome!

Thanks,
Qi

Qi Zheng (7):
  mm: change mm/pt_reclaim.c to use asm/tlb.h instead of
    asm-generic/tlb.h
  alpha: mm: enable MMU_GATHER_RCU_TABLE_FREE
  LoongArch: mm: enable MMU_GATHER_RCU_TABLE_FREE
  mips: mm: enable MMU_GATHER_RCU_TABLE_FREE
  parisc: mm: enable MMU_GATHER_RCU_TABLE_FREE
  um: mm: enable MMU_GATHER_RCU_TABLE_FREE
  mm: make PT_RECLAIM depends on MMU_GATHER_RCU_TABLE_FREE

 arch/alpha/Kconfig                   | 1 +
 arch/alpha/include/asm/tlb.h         | 6 +++---
 arch/loongarch/Kconfig               | 1 +
 arch/loongarch/include/asm/pgalloc.h | 7 +++----
 arch/mips/Kconfig                    | 1 +
 arch/mips/include/asm/pgalloc.h      | 7 +++----
 arch/parisc/Kconfig                  | 1 +
 arch/parisc/include/asm/tlb.h        | 4 ++--
 arch/um/Kconfig                      | 1 +
 arch/x86/Kconfig                     | 1 -
 mm/Kconfig                           | 9 ++-------
 mm/pt_reclaim.c                      | 2 +-
 12 files changed, 19 insertions(+), 22 deletions(-)

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2.20.1