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Date: Thu, 16 Jun 2016 14:54:56 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Minchan Kim <minchan@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>, Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@suse.com>,
        Hillf Danton <hillf.zj@alibaba-inc.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: compaction: fix dummy declarations
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On Thu, 16 Jun 2016 08:30:28 +0900 Minchan Kim <minchan@kernel.org> wrote:

> Hi Andrew,
> 
> On Wed, Jun 15, 2016 at 02:48:25PM -0700, Andrew Morton wrote:
> > On Wed, 15 Jun 2016 23:39:12 +0200 Arnd Bergmann <arnd@arndb.de> wrote:
> > 
> > > We get a build error in several test builds after a recent code rework:
> > > 
> > > In file included from include/linux/balloon_compaction.h:48:0,
> > >                  from mm/balloon_compaction.c:11:
> > > include/linux/compaction.h:237:122: error: 'struct node' declared inside parameter list will not be visible outside of this definition or declaration [-Werror]
> > > 
> > > The patch that likely introduced the problem added a forward declaration
> > > for 'struct node' in linux/compaction.h, but only in one of two instances.
> > > 
> > > This moves the declaration out of the #ifdef so we always get it.
> > 
> > http://ozlabs.org/~akpm/mmots/broken-out/mm-balloon-use-general-non-lru-movable-page-feature-fix.patch
> > should fix this.  I guess I should do another -mm.
> > 
> 
> [1] solves the issues so we can revert your patch with removing remaining
> forward declaration in below code snippet.
> If I should resend patch with removing remainiang forward declaration part,
> please tell me.
> 
> Thanks.
> 
> compaction.h:
> 
> #if defined(CONFIG_COMPACTION) && defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
> struct node; <----- Here
> extern int compaction_register_node(struct node *node);
> ...
> #else
> ...
> 
> #endif /* CONFIG_COMPACTION && CONFIG_SYSFS && CONFIG_NUMA */
> 
> 
> [1] http://ozlabs.org/~akpm/mmots/broken-out/mm-fix-build-warnings-in-linux-compactionh.patch
> 

I think I'll retain
mm-balloon-use-general-non-lru-movable-page-feature-fix.patch for
bisectability reasons and I'll revert
mm-balloon-use-general-non-lru-movable-page-feature-fix.patc within
mm-fix-build-warnings-in-linux-compactionh.patch, see how that goes.