[PATCH v18 0/3] Improve proc RSS accuracy

This series introduces the hierarchical tree counter (hpcc) to increase
accuracy of approximated RSS counters exposed through proc interfaces.

With a test program hopping across CPUs doing frequent mmap/munmap
operations, the upstream implementation approximation reaches a 1GB
delta from the precise value after a few minutes, compared to a 80MB
delta with the hierarchical counter. The hierarchical counter provides a
guaranteed maximum approximation inaccuracy of 192MB on that hardware
topology.

This series is based on tag v7.0-rc1.

The main changes since v17:
- Fix patch series bissectability.
- Export GPL symbols for kunit tests.
- Improve kunit tests coverage.
- Fix kunit tests wait queue head reinit bug.
- Fix an out-of-bound on bootup on configurations where nr_cpu_ids is
  close to NR_CPUS.

Andrew, this series targets 7.1.

Thanks!

Mathieu

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Lameter <redacted>
Cc: Martin Liu <redacted>
Cc: David Rientjes <rientjes@google.com>
Cc: christian.koenig@amd.com
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: SeongJae Park <sj@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Sweet Tea Dorminy <redacted>
Cc: Lorenzo Stoakes <redacted>
Cc: "Liam R . Howlett" <redacted>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <redacted>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Wei Yang <redacted>
Cc: David Hildenbrand <redacted>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-mm@kvack.org
Cc: linux-trace-kernel@vger.kernel.org
Cc: Yu Zhao <redacted>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Mateusz Guzik <redacted>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Aboorva Devarajan <redacted>

Mathieu Desnoyers (3):
  lib: Introduce hierarchical per-cpu counters
  lib: Test hierarchical per-cpu counters
  mm: Improve RSS counter approximation accuracy for proc interfaces

 .../core-api/percpu-counter-tree.rst          |  75 ++
 include/linux/mm.h                            |  19 +-
 include/linux/mm_types.h                      |  54 +-
 include/linux/percpu_counter_tree.h           | 367 +++++++++
 include/trace/events/kmem.h                   |   2 +-
 init/main.c                                   |   2 +
 kernel/fork.c                                 |  22 +-
 lib/Kconfig                                   |  12 +
 lib/Makefile                                  |   1 +
 lib/percpu_counter_tree.c                     | 702 ++++++++++++++++++
 lib/tests/Makefile                            |   2 +
 lib/tests/percpu_counter_tree_kunit.c         | 399 ++++++++++
 12 files changed, 1627 insertions(+), 30 deletions(-)
 create mode 100644 Documentation/core-api/percpu-counter-tree.rst
 create mode 100644 include/linux/percpu_counter_tree.h
 create mode 100644 lib/percpu_counter_tree.c
 create mode 100644 lib/tests/percpu_counter_tree_kunit.c

-- 
2.39.5