linux-kernel - Re: [PATCH] sparsemem vmemmap: initialize memmap.

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Date:	Fri, 9 May 2008 11:31:46 +0100
From:	Andy Whitcroft <apw@...dowen.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <clameter@....com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] sparsemem vmemmap: initialize memmap.

On Fri, May 09, 2008 at 08:38:56AM +0200, Heiko Carstens wrote:
> From: Heiko Carstens <heiko.carstens@...ibm.com>
> 
> Trying to online a new memory section that was added via memory hotplug
> results in lots of messages of pages in bad page state.
> Reason is that the alloacted virtual memmap isn't initialized.
> This is only an issue for memory sections that get added after boot
> time since for all other memmaps the bootmem allocator was used which
> returns only initialized memory.
> 
> I noticed this on s390 which has its private vmemmap_populate function
> without using callbacks to the common code. But as far as I can see the
> generic code has the same bug, so fix it just once.
> 
> Cc: Andy Whitcroft <apw@...dowen.org>
> Cc: Christoph Lameter <clameter@....com>
> Cc: Gerald Schaefer <gerald.schaefer@...ibm.com>
> Signed-off-by: Heiko Carstens <heiko.carstens@...ibm.com>
> ---
>  mm/sparse-vmemmap.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6/mm/sparse-vmemmap.c
> ===================================================================
> --- linux-2.6.orig/mm/sparse-vmemmap.c
> +++ linux-2.6/mm/sparse-vmemmap.c
> @@ -154,6 +154,6 @@ struct page * __meminit sparse_mem_map_p
>  	int error = vmemmap_populate(map, PAGES_PER_SECTION, nid);
>  	if (error)
>  		return NULL;
> -
> +	memset(map, 0, PAGES_PER_SECTION * sizeof(struct page));
>  	return map;
>  }

The normal expectation is that all allocations are made using
vmemmap_alloc_block() which allocates from the appropriate place.  Once
the buddy is up and available it uses:

	struct page *page = alloc_pages_node(node,
			GFP_KERNEL | __GFP_ZERO, get_order(size));

to get the memory so it should all be zero'd.  So I would expect all
existing users to be covered by that?  Can you not simply use __GFP_ZERO
for your allocations or use vmemmap_alloc_block() ?

-apw
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