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Subject[PATCH V5 0/3] percpu_ref & block: reduce memory footprint of percpu_ref in fast path
Date
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>
--
2.25.2

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