[PATCH v4 0/8] enable PT_RECLAIM on more 64-bit architectures

[Qi Zheng]

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

Changes in v4:
 - convert __HAVE_ARCH_TLB_REMOVE_TABLE to CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE config
 - fix a WARN_ON_ONCE() on sparc64 (and on ppc)
   (reported by Andreas Larsson)
 - collect Acked-by (Hi David, I've kept your Acked-by, feel free to drop it)
 - rebase onto the v6.19-rc7

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 more 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.

For these architectures that define its own __tlb_remove_table(), since
their page tables are not of type struct ptdesc, they cannot be supported
PT_RECLAIM.

Therefore, this series first enables MMU_GATHER_RCU_TABLE_FREE on all 64-bit
architectures, then converts __HAVE_ARCH_TLB_REMOVE_TABLE to
CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE config, and finally makes PT_RECLAIM depend on
MMU_GATHER_RCU_TABLE_FREE && !HAVE_ARCH_TLB_REMOVE_TABLE. This way, PT_RECLAIM
can be enabled by default on most 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 (8):
  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: convert __HAVE_ARCH_TLB_REMOVE_TABLE to
    CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE config
  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/powerpc/Kconfig                 | 1 +
 arch/powerpc/include/asm/tlb.h       | 1 -
 arch/sparc/Kconfig                   | 1 +
 arch/sparc/include/asm/tlb_64.h      | 1 -
 arch/um/Kconfig                      | 1 +
 arch/x86/Kconfig                     | 1 -
 include/asm-generic/tlb.h            | 2 +-
 mm/Kconfig                           | 8 +++-----
 mm/pt_reclaim.c                      | 2 +-
 17 files changed, 23 insertions(+), 23 deletions(-)

-- 
2.20.1