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Date: Tue, 6 Jan 2015 20:53:19 -0800
Message-ID: <CA+55aFyLWFYzLkE3orkxKsGciq5eUEtcJE5L0uypNZFcW3h2HQ@mail.gmail.com>
Subject: Re: [PATCH V3 0/4] Reducing parameters of alloc_pages* family of functions
From: Linus Torvalds <torvalds@linux-foundation.org>
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Sender: owner-linux-mm@kvack.org
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To: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-mm <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>, David Rientjes <rientjes@google.com>, Johannes Weiner <hannes@cmpxchg.org>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@suse.cz>, Minchan Kim <minchan@kernel.org>, Rik van Riel <riel@redhat.com>, Zhang Yanfei <zhangyanfei@cn.fujitsu.com>

On Mon, Jan 5, 2015 at 8:01 AM, Vlastimil Babka <vbabka@suse.cz> wrote:
>
> Hm, nope. The !CONFIG_COMPACTION variant of try_to_compact_pages() is static
> inline that returns COMPACT_CONTINUE, which is defined in compaction.h.
> Another solution is to add a "forward" declaration (not actually followed later
> by a full definition) of struct alloc_context into compaction.h. Seems to work
> here, but I'm not sure if such thing is allowed?

We do forward struct declarations quite often (well, _relatively_
often) in order to avoid nasty circular header includes, and sometimes
just to avoid unnecessarily many header includes.

See for example

    git grep '\<struct [a-zA-Z_0-9]*;'

it's not exactly rare.

So it's fine.

                        Linus

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