linux-kernel - Re: [PATCH v4 3/4] mm/pageblock: work around multiple arch's cmpxchg support issue

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Date:   Thu, 10 Sep 2020 06:51:12 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        David Hildenbrand <david@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Alexander Duyck <alexander.duyck@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Russell King <linux@...linux.org.uk>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-xtensa@...ux-xtensa.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 3/4] mm/pageblock: work around multiple arch's cmpxchg
 support issue

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.