linux-kernel - Re: [PATCH V2 0/2] percpu_ref & block: reduce memory footprint of percpu

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Message-ID: <4ce7b53b-2c42-3814-fa0a-5324aca6aae0@kernel.dk>
Date:   Wed, 2 Sep 2020 08:02:30 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Ming Lei <ming.lei@...hat.com>, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org
Cc:     Sagi Grimberg <sagi@...mberg.me>, Tejun Heo <tj@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Bart Van Assche <bvanassche@....org>
Subject: Re: [PATCH V2 0/2] percpu_ref & block: reduce memory footprint of
 percpu_ref in fast path

On 9/2/20 6:26 AM, Ming Lei wrote:
> 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.
> 
> 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'

Applied, thanks.

-- 
Jens Axboe