linux-kernel - Re: [PATCH] mm: create a separate slab for page->ptl allocation

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Message-ID: <20131106132155.GA22132@shutemov.name>
Date:	Wed, 6 Nov 2013 15:21:55 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-arch@...r.kernel.org
Subject: Re: [PATCH] mm: create a separate slab for page->ptl allocation

On Wed, Nov 06, 2013 at 10:31:31AM +0100, Peter Zijlstra wrote:
> On Wed, Nov 06, 2013 at 01:13:11AM +0200, Kirill A. Shutemov wrote:
> > I would like to get rid of __ptlock_alloc()/__ptlock_free() too, but I
> > don't see a way within C: we need to know sizeof(spinlock_t) on
> > preprocessor stage.
> > 
> > We can have a hack on kbuild level: write small helper program to find out
> > sizeof(spinlock_t) before start building and turn it into define.
> > But it's overkill from my POV. And cross-compilation will be a fun.
> 
> Ah, I just remembered, we have such a thing!

Great!

> @@ -1354,7 +1356,7 @@ static inline bool ptlock_init(struct page *page)
>  	 * slab code uses page->slab_cache and page->first_page (for tail
>  	 * pages), which share storage with page->ptl.
>  	 */
> -	VM_BUG_ON(page->ptl);
> +	VM_BUG_ON(*(unsigned long *)&page->ptl);

Huh? Why not direct cast to unsigned long?

VM_BUG_ON((unsigned long)page->ptl);

Otherwise:

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>


-- 
 Kirill A. Shutemov
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