linux-kernel - Re: [PATCH] Move page_assign_page_cgroup to VM_BUG_ON in free_hot_cold

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Message-ID: <Pine.LNX.4.64.0712201312490.17015@blonde.wat.veritas.com>
Date:	Thu, 20 Dec 2007 13:14:30 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Dave Hansen <haveblue@...ibm.com>
cc:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Move page_assign_page_cgroup to VM_BUG_ON in free_hot_cold_page

On Wed, 19 Dec 2007, Dave Hansen wrote:
> > --- linux-2.6.24-rc5/mm/page_alloc.c~memory-controller-move-to-bug-on-in-free_hot_cold_page     2007-12-19 11:31:46.000000000 +0530
> > +++ linux-2.6.24-rc5-balbir/mm/page_alloc.c     2007-12-19 11:33:45.000000000 +0530
> > @@ -995,7 +995,7 @@ static void fastcall free_hot_cold_page(
> >  
> >         if (!PageHighMem(page))
> >                 debug_check_no_locks_freed(page_address(page), PAGE_SIZE);
> > -       page_assign_page_cgroup(page, NULL);
> > +       VM_BUG_ON(page_get_page_cgroup(page));
> >         arch_free_page(page, 0);
> >         kernel_map_pages(page, 1, 0); 
> 
> Hi Balbir,
> 
> You generally want to do these like:
> 
> 	foo = page_assign_page_cgroup(page, NULL);
> 	VM_BUG_ON(foo);
> 
> Some embedded people have been known to optimize kernel size like this:
> 
> 	#define VM_BUG_ON(x) do{}while(0)

Balbir's patch looks fine to me: I don't get your point there, Dave.

Hugh
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