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Date:   Thu, 10 Sep 2020 06:51:12 +0100
From:   Christoph Hellwig <hch@infradead.org>
To:     Alex Shi <alex.shi@linux.alibaba.com>
Cc:     Anshuman Khandual <anshuman.khandual@arm.com>,
        David Hildenbrand <david@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Alexander Duyck <alexander.duyck@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Russell King <linux@armlinux.org.uk>,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
        "David S. Miller" <davem@davemloft.net>,
        Chris Zankel <chris@zankel.net>,
        Max Filippov <jcmvbkbc@gmail.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
        linux-xtensa@linux-xtensa.org, linux-mm@kvack.org
Subject: Re: [PATCH v4 3/4] mm/pageblock: work around multiple arch's cmpxchg
 support issue
Message-ID: <20200910055112.GA11727@infradead.org>
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On Thu, Sep 03, 2020 at 03:01:22PM +0800, Alex Shi wrote:
> Armv6, sh2, sparc32 and xtensa can not do cmpxchg1, so we have to use
> cmpxchg4 on it.
> 
> Here we mark above 4 arch's NO_CMPXCHG_BYTE, and would add more if we
> found.
> 
> This is the first usages of cmpxchg flase sharing change. We'd better
> check more cmpxchg usages in current kernel...

I think a positive symbol, e.g. HAVE_CMPXCHG_BYTE is a lot easier to
understand, and also fool-proof.