linux-kernel - Re: [PATCH] mm: Make {,set}page_address() static inline if WANT_PAGE

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Message-ID: <alpine.DEB.2.02.1401151454440.24121@chino.kir.corp.google.com>
Date:	Wed, 15 Jan 2014 14:57:56 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Guenter Roeck <linux@...ck-us.net>,
	"Michael S. Tsirkin" <mst@...hat.com>, linux-mm@...ck.org,
	linux-bcache@...r.kernel.org, Vineet Gupta <vgupta@...opsys.com>,
	sparclinux@...r.kernel.org, linux-m68k@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: Make {,set}page_address() static inline if
 WANT_PAGE_VIRTUAL

On Wed, 15 Jan 2014, Geert Uytterhoeven wrote:

> {,set}page_address() are macros if WANT_PAGE_VIRTUAL.
> If !WANT_PAGE_VIRTUAL, they're plain C functions.
> 
> If someone calls them with a void *, this pointer is auto-converted to
> struct page * if !WANT_PAGE_VIRTUAL, but causes a build failure on
> architectures using WANT_PAGE_VIRTUAL (arc, m68k and sparc):

s/sparc/sparc64/

> 
> drivers/md/bcache/bset.c: In function ‘__btree_sort’:
> drivers/md/bcache/bset.c:1190: warning: dereferencing ‘void *’ pointer
> drivers/md/bcache/bset.c:1190: error: request for member ‘virtual’ in something not a structure or union
> 
> Convert them to static inline functions to fix this. There are already
> plenty of  users of struct page members inside <linux/mm.h>, so there's no
> reason to keep them as macros.
> 
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Tested-by: David Rientjes <rientjes@...gle.com>

I'm cringing at the page_address(mempool_alloc(..., GFP_NOIO)) in 
drivers/md/bcache/bset.c, though.  It's relying on that fact that 
mempool_alloc() can never return NULL if __GFP_WAIT but I think this could 
have all been avoided with

	struct page *page = mempool_alloc(state->pool, GFP_NOIO);
	out = page_address(page);

instead of burying the mempool_alloc() in page_address() for what I think 
is cleaner code.  Owell, it fixes the issue.