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

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Message-Id: <1198084473.15321.48.camel@localhost>
Date:	Wed, 19 Dec 2007 09:14:33 -0800
From:	Dave Hansen <haveblue@...ibm.com>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	Hugh Dickins <hugh@...itas.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, 2007-12-19 at 11:48 +0530, Balbir Singh wrote:
> diff -puN mm/page_alloc.c~memory-controller-move-to-bug-on-in-free_hot_cold_page mm/page_alloc.c
> --- 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)

-- Dave

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