linux-kernel - RE: [PATCH 01/15] sched: convert sighand_struct.count to refcount

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Date:   Mon, 23 Oct 2017 12:26:47 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Reshetova, Elena" <elena.reshetova@...el.com>
cc:     "mingo@...hat.com" <mingo@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
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        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
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        <alexander.shishkin@...ux.intel.com>,
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        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>
Subject: RE: [PATCH 01/15] sched: convert sighand_struct.count to
 refcount_t

On Mon, 23 Oct 2017, Reshetova, Elena wrote:
> > On Fri, 20 Oct 2017, Elena Reshetova wrote:
> > How did you make sure that these atomic operations have no other
> > serialization effect and can be replaced with refcount?
> 
> What serialization effects? Are you taking about smth else than memory
> ordering? 

Well, the memory ordering constraints can be part of serialization
mechanisms. Unfortunately they are not well documented ....

> For memory ordering my current hope is that we can just make refcount_t
> to use same strict atomic primitives and then it would not make any
> difference.  I think this would be the simplest way for everyone since I
> think even some maintainers are having issues understanding all the
> implications of "relaxed" ordering.

Well, that would make indeed the conversion simpler because then it is just
a drop in replacement. Albeit there might be some places which benefit of
the relaxed ordering as on some architectures strict ordering is expensive.

Thanks,

	tglx