linux-kernel - Re: [PATCH v2 2/2] writeback: Rework wb_[dec|inc]

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Message-ID: <20170620193715.GF21326@htj.duckdns.org>
Date:   Tue, 20 Jun 2017 15:37:15 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Nikolay Borisov <nborisov@...e.com>
Cc:     jbacik@...com, linux-kernel@...r.kernel.org,
        mgorman@...hsingularity.net
Subject: Re: [PATCH v2 2/2] writeback: Rework wb_[dec|inc]_stat family of
 functions

Hello, Nikolay.

On Tue, Jun 20, 2017 at 09:02:00PM +0300, Nikolay Borisov wrote:
> Currently the writeback statistics code uses a percpu counters to hold
> various statistics. Furthermore we have 2 families of functions - those which
> disable local irq and those which doesn't and whose names begin with
> double underscore. However, they both end up calling __add_wb_stats which in
> turn calls percpu_counter_add_batch which is already irq-safe.

Heh, looks like I was confused.  __percpu_counter_add() is not
irq-safe.  It disables preemption and uses __this_cpu_read(), so
there's no protection against irq.  If writeback statistics want
irq-safe operations and it does, it would need these separate
operations.  Am I missing something?

Thanks.

-- 
tejun