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[V5,0/3] percpu_ref & block: reduce memory footprint of percpu_ref in fast path

Message ID 20200927062654.2750277-1-ming.lei@redhat.com (mailing list archive)
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Series percpu_ref & block: reduce memory footprint of percpu_ref in fast path | expand

Message

Ming Lei Sept. 27, 2020, 6:26 a.m. UTC 
Hi,

The 1st patch removes memory footprint of percpu_ref in fast path
from 7 words to 2 words, since it is often used in fast path and
embedded in user struct.

The 2nd patch moves .q_usage_counter to 1st cacheline of
'request_queue'.

Simple test on null_blk shows ~2% IOPS boost on one 16cores(two threads
per core) machine, dual socket/numa.

V5:
	- fix memory leak on ref->data, only percpu_ref_exit() of patch 2
	is modified.

V4:
	- rename percpu_ref_inited as percpu_ref_is_initialized

V3:
	- fix kernel oops on MD
	- add patch for avoiding to use percpu-refcount internal from md
	  code
	- pass Red Hat CKI test which is done by Veronika Kabatova

V2:
	- pass 'gfp' to kzalloc() for fixing block/027 failure reported by
	kernel test robot
	- protect percpu_ref_is_zero() with destroying percpu-refcount by
	spin lock  


Ming Lei (3):
  percpu_ref: add percpu_ref_is_initialized for MD
  percpu_ref: reduce memory footprint of percpu_ref in fast path
  block: move 'q_usage_counter' into front of 'request_queue'

 drivers/infiniband/sw/rdmavt/mr.c |   2 +-
 drivers/md/md.c                   |   2 +-
 include/linux/blkdev.h            |   3 +-
 include/linux/percpu-refcount.h   |  46 ++++------
 lib/percpu-refcount.c             | 137 +++++++++++++++++++++++-------
 5 files changed, 126 insertions(+), 64 deletions(-)

Cc: Veronika Kabatova <vkabatov@redhat.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Bart Van Assche <bvanassche@acm.org>