Date:   Mon, 6 Dec 2021 18:19:56 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Christoph Hellwig <hch@infradead.org>,
        "linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
        keescook@chromium.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] block: switch to atomic_t for request references
Message-ID: <Ya5GPJm+S1sgpDGj@hirez.programming.kicks-ass.net>
References: <9f2ad6f1-c1bb-dfac-95c8-7d9eaa7110cc@kernel.dk>
 <Ya2zfVAwh4aQ7KVd@infradead.org>
 <Ya3KZiLg5lYjsGcQ@hirez.programming.kicks-ass.net>
 <dbe2b14c-5f0a-80dd-b661-d0a7c74ba230@kernel.dk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <dbe2b14c-5f0a-80dd-b661-d0a7c74ba230@kernel.dk>
Precedence: bulk

On Mon, Dec 06, 2021 at 09:32:06AM -0700, Jens Axboe wrote:
> On 12/6/21 1:31 AM, Peter Zijlstra wrote:
> > On Sun, Dec 05, 2021 at 10:53:49PM -0800, Christoph Hellwig wrote:
> >> On Fri, Dec 03, 2021 at 08:35:40AM -0700, Jens Axboe wrote:
> >>> refcount_t is not as expensive as it used to be, but it's still more
> >>> expensive than the io_uring method of using atomic_t and just checking
> >>> for potential over/underflow.
> >>>
> >>> This borrows that same implementation, which in turn is based on the
> >>> mm implementation from Linus.
> >>
> >> If refcount_t isn't good enough for a normal kernel fast path we have
> >> a problem.  Can we discuss that with the maintainers instead of coming
> >> up with our home grown schemes again?
> > 
> > Quite; and for something that pretends to be about performance, it also
> > lacks any actual numbers to back that claim.
> 
> I can certainly generate that, it was already done for the two previous
> similar conversions though.

I've never seen those :-(