[PATCH v2 0/3] sched/numa: refine memory tiering promotion heuristics

[Li Zhe]

This version narrows the series to memory tiering.  The generic normal
NUMA balancing cleanups and heuristic changes from v1 are not included.

Patch 1 makes the free-space promotion bypass configurable while keeping
the existing eager-promotion behavior as the default.  Disabling the
bypass forces slow-tier promotions through the normal hotness and
rate-limit checks, which helps workloads that intentionally keep part of
their memory on a slow tier avoid short cold bursts refilling the fast
tier.

Patch 2 keeps memory-tiering-only promotion faults out of normal AutoNUMA
task-placement statistics.  Slow-tier NUMA hint faults use the folio
last-cpupid field as access-time metadata, so those faults should not be
interpreted as normal placement feedback.  The patch marks them explicitly
and skips the placement accounting path.

Patch 3 builds on that separation.  Once tiering faults are no longer fed
into task placement stats, tiering-only mode can use tiering-specific
outcomes to tune the scan period: hot feedback speeds scanning up, while
cold, throttled, failed or empty windows slow it down.  This prevents
tiering-only promotion feedback from being handled by the normal placement
heuristic, where repeated promotions can otherwise push the scan period
towards the maximum.

Li Zhe (3):
  sched/numa: make free-space tiering promotion bypass configurable
  sched/numa: do not feed tiering promotions into task placement stats
  sched/numa: fix scan-period adjustment for tiering-only mode

 include/linux/mmzone.h               |   5 +-
 include/linux/sched.h                |  17 ++++
 include/linux/sched/numa_balancing.h |  10 ++
 kernel/sched/debug.c                 |   2 +
 kernel/sched/fair.c                  | 140 +++++++++++++++++++++++++--
 kernel/sched/sched.h                 |   1 +
 mm/memory.c                          |   6 +-
 7 files changed, 168 insertions(+), 13 deletions(-)

---
v1: https://lore.kernel.org/all/20261014094347.99157-1-lizhe.67@xxxxxxxxxxxxx/

Changes since v1:
- Dropped the generic normal NUMA balancing patches.
- Added patch 3 to dynamically adjust the scan period in
  memory-tiering-only mode.

-- 
2.20.1