Merge tag 'percpu-for-6.6' of git://git.kernel.org/pub/scm/linux/kernel/git/dennis/percpu

Pull percpu updates from Dennis Zhou:
 "One bigger change to percpu_counter's api allowing for init and
  destroy of multiple counters via percpu_counter_init_many() and
  percpu_counter_destroy_many(). This is used to help begin remediating
  a performance regression with percpu rss stats.

  Additionally, it seems larger core count machines are feeling the
  burden of the single threaded allocation of percpu. Mateusz is
  thinking about it and I will spend some time on it too.

  percpu:

   - A couple cleanups by Baoquan He and Bibo Mao. The only behavior
     change is to start printing messages if we're under the warn limit
     for failed atomic allocations.

  percpu_counter:

   - Shakeel introduced percpu counters into mm_struct which caused
     percpu allocations be on the hot path [1]. Originally I spent some
     time trying to improve the percpu allocator, but instead preferred
     what Mateusz Guzik proposed grouping at the allocation site,
     percpu_counter_init_many(). This allows a single percpu allocation
     to be shared by the counters. I like this approach because it
     creates a shared lifetime by the allocations. Additionally, I
     believe many inits have higher level synchronization requirements,
     like percpu_counter does against HOTPLUG_CPU. Therefore we can
     group these optimizations together"

Link: https://lore.kernel.org/linux-mm/20221024052841.3291983-1-shakeelb@google.com/ [1]

* tag 'percpu-for-6.6' of git://git.kernel.org/pub/scm/linux/kernel/git/dennis/percpu:
  kernel/fork: group allocation/free of per-cpu counters for mm struct
  pcpcntr: add group allocation/free
  mm/percpu.c: print error message too if atomic alloc failed
  mm/percpu.c: optimize the code in pcpu_setup_first_chunk() a little bit
  mm/percpu.c: remove redundant check
  mm/percpu: Remove some local variables in pcpu_populate_pte

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