[PATCH 0/7 V2] workqueue: cleanup for attr management

[Lai Jiangshan <laijs@cn.fujitsu.com>]

Hi,

This is the V2 version of the V1 pathset.  But it is just the updated
version of the patch1&2 of the V1 patchset.

[1/5 V1] is split into [1/7 V2] and [2/7 V2].
[2/5 V1] is split into [3,4,5,6,7/7 V2].

[1/7] extends the wq_pool_mutex lock region in the apply_workqueue_attrs().
	It is a basic patch for all the later patches except the [6/7 V2].
[2/7] simplifies wq_update_unbound_numa() since lock requirement is eased.

[3/7] introduces get_pwq_unlocked() for reusing existing pwqs
	It is also a basic patch for all the later patches except the [6/7 V2].
[4,5,6/7] apply the good code of wq_update_unbound_numa() to
	     apply_workqueue_attrs(): reuse the unchanged per-node/default pwq
	     and reuse the preallocated wq_update_unbound_numa_attrs_buf.

[2,3,4,5,6/7] try to make the per-node allocation are the same in
	wq_update_unbound_numa() and apply_workqueue_attrs(), but they
	are not exactly the same. wq_update_unbound_numa() directly returns
	when the pwq unchanged.

[7/7] adds get_node_unbound_pwq() which uses the per-node allocation
	behavior of the apply_workqueue_attrs().  So wq_update_unbound_numa()
	has some overhead introduced.  But cpu-hotplug path is cold path,
	it is Ok.

	It removes some comments without adding the corresponding ones back.

Other changed from V1:
	The unneeded comment about the stableness of the wq->unbound_attrs
	is removed in [2/7].

	alloc_node_unbound_pwq() is renamed to get_node_unbound_pwq().
	@use_dfl_when_fail is removed from get_node_unbound_pwq().
	get_node_unbound_pwq() is shorter under the help of get_pwq_unlocked().

	apply_wqattrs_cleanup() is not protected by wq_pool_mutex

	some comment revised as TJ's suguested.

Thanks,
Lai

Cc: Tejun Heo <tj@kernel.org>

Lai Jiangshan (7):
  workqueue: wq_pool_mutex protects the attrs-installation
  workqueue: simplify wq_update_unbound_numa()
  workqueue: introduce get_pwq_unlocked()
  workqueue: reuse the current per-node pwq when its attrs unchanged
  workqueue: reuse the current default pwq when its attrs unchanged
  workqueue: reuse wq_update_unbound_numa_attrs_buf as temporary attrs
  workqueue: add get_node_unbound_pwq()

 kernel/workqueue.c | 197 ++++++++++++++++++++++++++---------------------------
 1 file changed, 95 insertions(+), 102 deletions(-)

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2.1.0
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