[PATCH v7 0/5] shoot lazy tlbs (lazy tlb refcount scalability improvement)

[Nicholas Piggin <npiggin@gmail.com>]

(Sorry about the double send)

Hi Andrew,

This series improves scalability of context switching between user and
kernel threads on large systems with a threaded process spread across a
lot of CPUs.

Please consider these patches for mm. Discussion of v6 here:

https://lore.kernel.org/linux-mm/20230118080011.2258375-1-npiggin@gmail.com/

No objections so far, Linus think they look okay in principle but has
not reviewed in detail.

With the exception of patch 1, there should be no functional change
on non-powerpc archs with this series.

Changes since v6:
- Dropped the final patch to optimise powerpc more, as mentioned this
  will be taken through the powerpc tree after the base series is
  upstream.
- Split the first patch into patch 1 and 2 in this series so the
  functional change is isolated to minimal patch.
- Removed ifdefs and churn from sched/core.c that were not required
  because ifdefs in .h refcount functions do the same job.
- Split DEBUG_VM option out to its own sub-option because it IPIs all
  CPUs on on every process exit which is pretty heavy.
- Changed comment style as noted by Nadav.
- Added description about how to test it, requested by Linus.
- Added link and credit to Rik's earlier work in the same vein.
- Did a pass over comments and changelogs to improve readability.

Nicholas Piggin (5):
  kthread: simplify kthread_use_mm refcounting
  lazy tlb: introduce lazy tlb mm refcount helper functions
  lazy tlb: allow lazy tlb mm refcounting to be configurable
  lazy tlb: shoot lazies, non-refcounting lazy tlb mm reference handling
    scheme
  powerpc/64s: enable MMU_LAZY_TLB_SHOOTDOWN

 Documentation/mm/active_mm.rst       |  6 +++
 arch/Kconfig                         | 32 ++++++++++++++
 arch/arm/mach-rpc/ecard.c            |  2 +-
 arch/powerpc/Kconfig                 |  1 +
 arch/powerpc/kernel/smp.c            |  2 +-
 arch/powerpc/mm/book3s64/radix_tlb.c |  4 +-
 fs/exec.c                            |  2 +-
 include/linux/sched/mm.h             | 28 ++++++++++++
 kernel/cpu.c                         |  2 +-
 kernel/exit.c                        |  2 +-
 kernel/fork.c                        | 65 ++++++++++++++++++++++++++++
 kernel/kthread.c                     | 22 ++++++----
 kernel/sched/core.c                  | 15 ++++---
 lib/Kconfig.debug                    | 10 +++++
 14 files changed, 170 insertions(+), 23 deletions(-)

-- 
2.37.2