[PATCH v2 0/9] workqueue: base pwq pool release and nr_active on the backing pool

[Breno Leitao]

The goal is to unify per-cpu and unbound workqueues onto one backend, so
an unbound workqueue can run on the concurrency-managed per-cpu pools and
WQ_PERCPU just requests that backend [1]. This series is preparation and
changes no behaviour on its own.

These changes also is a reasonable readability cleanup.

Design principles, as discussed in [2].

 a) There is one workqueue implementation -- what is today the unbound one --
    and percpu becomes one of its affinity settings rather than a separate
    type. The unbound_* helper names get renamed/removed once they stop
    being unbound-specific. So, `alloc_unbound_pwq()` becomes
    `alloc_pwq` and handle both cases.

 b) There is one pwq path, and alloc_and_link_percpu_pwqs() goes away.

 c) Which pool backs a pwq becomes a property of the attrs, resolved in
    alloc_unbound_pwq(), which hands out either the static percpu pool for
    that CPU or a hashed unbound one.

 d) Both pool types stay -- concurrency management only exists on the percpu
    ones -- so what gets merged is the machinery, not the pools.

 e) This is the prep phase for the changes that will come once we are
    happy with these changes.

What will come later:

  * Introduce a concurrency-managed per-cpu affinity scope
    (WQ_AFFN_PERCPU) — percpu as an affinity setting

  * Direct pool selection (fold the create-then-convert),

  * Dynamic switching between per-cpu and unbound backing for CPU isolation.

[1] https://lore.kernel.org/all/ak569WYSm3ygKl1-@xxxxxxxxxxxxxxx
[2] https://lore.kernel.org/all/anDImojbi6lq0zUg@xxxxxxxxxxxxxxx/

Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
Changes in v2:
- Removed the ugly __WQ_PERCPU_POOLS
- Renamed some helpers here and there
- additional patches, removing the "unbound" from function names
- Link to v1: https://patch.msgid.link/20260731-wq-pool-refactor-v1-0-8eaf71cdab5f@xxxxxxxxxx

---
Breno Leitao (9):
      workqueue: factor out get_percpu_pool()
      workqueue: factor out alloc_and_link_percpu_pwqs()
      workqueue: release pwq pools by pool type
      workqueue: account nr_active by the backing pool
      workqueue: test WQ_UNBOUND explicitly in the hotplug loops
      workqueue: rename wq->unbound_attrs to wq->attrs
      workqueue: allocate attrs for all workqueues
      workqueue: rename alloc_unbound_pwq() to alloc_pwq()
      workqueue: skip the node_nr_active update for non-unbound workqueues

 kernel/workqueue.c         | 166 +++++++++++++++++++++++++--------------------
 tools/workqueue/wq_dump.py |   6 +-
 2 files changed, 96 insertions(+), 76 deletions(-)
---
base-commit: dbff1ec23f68640a743512e8ada125795d1b72c7
change-id: 20260729-wq-pool-refactor-0fb28721f83f

Best regards,
--  
Breno Leitao <leitao@xxxxxxxxxx>