linux-kernel - [PATCH V6 0/2] percpu_ref & block: reduce memory footprint of percpu

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Date:   Wed, 30 Sep 2020 16:26:55 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Cc:     Ming Lei <ming.lei@...hat.com>,
        Veronika Kabatova <vkabatov@...hat.com>,
        Sagi Grimberg <sagi@...mberg.me>, Tejun Heo <tj@...nel.org>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Bart Van Assche <bvanassche@....org>
Subject: [PATCH V6 0/2] percpu_ref & block: reduce memory footprint of percpu_ref in fast path

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.

V6:
	- drop the 1st patch which adds percpu_ref_is_initialized() for MD
	only, since Christoph doesn't like it

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 (2):
  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 +-
 include/linux/blkdev.h            |   3 +-
 include/linux/percpu-refcount.h   |  45 ++++------
 lib/percpu-refcount.c             | 131 ++++++++++++++++++++++--------
 4 files changed, 118 insertions(+), 63 deletions(-)

Cc: Veronika Kabatova <vkabatov@...hat.com>
Cc: Sagi Grimberg <sagi@...mberg.me>
Cc: Tejun Heo <tj@...nel.org>
Cc: Christoph Hellwig <hch@....de>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Bart Van Assche <bvanassche@....org>
-- 
2.25.2