linux-kernel - Re: [PATCH] block: switch to atomic

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Message-ID: <Ya5GPJm+S1sgpDGj@hirez.programming.kicks-ass.net>
Date:   Mon, 6 Dec 2021 18:19:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Christoph Hellwig <hch@...radead.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        keescook@...omium.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: switch to atomic_t for request references

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 :-(