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Date: Fri, 4 Jul 2014 11:16:39 +1000
From: Dave Chinner <david@fromorbit.com>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Konstantin Khlebnikov <koct9i@gmail.com>,
        Wu Fengguang <fengguang.wu@intel.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Borislav Petkov <bp@alien8.de>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Rusty Russell <rusty@rustcorp.com.au>,
        David Miller <davem@davemloft.net>,
        Andres Freund <andres@2ndquadrant.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Dave Hansen <dave.hansen@intel.com>,
        Christoph Hellwig <hch@infradead.org>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Linux API <linux-api@vger.kernel.org>,
        Naoya Horiguchi <nao.horiguchi@gmail.com>
Subject: Re: [PATCH v2 1/4] define PAGECACHE_TAG_* as enumeration under
 include/uapi
Message-ID: <20140704011639.GG9508@dastard>
References: <1404424335-30128-1-git-send-email-n-horiguchi@ah.jp.nec.com>
 <1404424335-30128-2-git-send-email-n-horiguchi@ah.jp.nec.com>
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On Thu, Jul 03, 2014 at 05:52:12PM -0400, Naoya Horiguchi wrote:
> We need the pagecache tags to be exported to userspace later in this
> series for fincore(2), so this patch moves the definition to the new
> include file for preparation. We also use the number of pagecache tags,
> so this patch also adds it.
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

NACK.

The radix tree tags are deeply internal implementation details.
They are an artifact of the current mark-and-sweep writeback
algorithm, and as such should never, ever be exposed to userspace,
let alone fixed in an ABI we need to support forever more.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com