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Message-ID: <alpine.DEB.2.20.1710231223450.4241@nanos>
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>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "tj@...nel.org" <tj@...nel.org>,
        "hannes@...xchg.org" <hannes@...xchg.org>,
        "lizefan@...wei.com" <lizefan@...wei.com>,
        "acme@...nel.org" <acme@...nel.org>,
        "alexander.shishkin@...ux.intel.com" 
        <alexander.shishkin@...ux.intel.com>,
        "eparis@...hat.com" <eparis@...hat.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "luto@...nel.org" <luto@...nel.org>,
        "keescook@...omium.org" <keescook@...omium.org>,
        "dvhart@...radead.org" <dvhart@...radead.org>,
        "ebiederm@...ssion.com" <ebiederm@...ssion.com>,
        "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

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