[PATCH v4 0/4] percpu: partial chunk depopulation

[Dennis Zhou <dennis@kernel.org>]

Hello,

This series is a continuation of Roman's series in [1]. It aims to solve
chunks holding onto free pages by adding a reclaim process to the percpu
balance work item.

The main difference is that the nr_empty_pop_pages is now managed at
time of isolation instead of intermixed. This helps with deciding which
chunks to free instead of having to interleave returning chunks to
active duty.

The allocation priority is as follows:
  1) appropriate chunk slot increasing until fit
  2) sidelined chunks
  3) full free chunks

The last slot for to_depopulate is never used for allocations.

A big thanks to Roman for initiating the work and being available for
iterating on these ideas.

This patchset contains the following 4 patches:
  0001-percpu-factor-out-pcpu_check_block_hint.patch
  0002-percpu-use-pcpu_free_slot-instead-of-pcpu_nr_slots-1.patch
  0003-percpu-implement-partial-chunk-depopulation.patch
  0004-percpu-use-reclaim-threshold-instead-of-running-for-.patch

0001 and 0002 are clean ups. 0003 implement partial chunk depopulation
initially from Roman. 0004 adds a reclaim threshold so we do not need to
schedule for every page freed.

This series is on top of percpu$for-5.14 67c2669d69fb.

diffstats below:

Dennis Zhou (2):
  percpu: use pcpu_free_slot instead of pcpu_nr_slots - 1
  percpu: use reclaim threshold instead of running for every page

Roman Gushchin (2):
  percpu: factor out pcpu_check_block_hint()
  percpu: implement partial chunk depopulation

 mm/percpu-internal.h |   5 +
 mm/percpu-km.c       |   5 +
 mm/percpu-stats.c    |  20 ++--
 mm/percpu-vm.c       |  30 ++++++
 mm/percpu.c          | 252 ++++++++++++++++++++++++++++++++++++++-----
 5 files changed, 278 insertions(+), 34 deletions(-)

Thanks,
Dennis