linux-kernel - Re: Pagecache: find_or_create_page does not call a proper page allocator function

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Message-Id: <20070423154224.15ebf8f7.akpm@linux-foundation.org>
Date:	Mon, 23 Apr 2007 15:42:24 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Nick Piggin <npiggin@...e.de>, linux-kernel@...r.kernel.org,
	pj@....com, Hugh Dickins <hugh@...itas.com>
Subject: Re: Pagecache: find_or_create_page does not call a proper page
 allocator function

On Mon, 23 Apr 2007 15:33:07 -0700 (PDT)
Christoph Lameter <clameter@....com> wrote:

> Grow dev page simply passes GFP_NOFS to find_or_create_page. This means the
> allocation of radix tree nodes is done with GFP_NOFS and the allocation
> of a new page is done using GFP_NOFS as well.
> 
> The mapping has a flags field that contains the necessary allocation flags for
> the page cache allocation. These need to be consulted in order to get DMA
> and HIGHMEM allocations etc right.
> 
> So fix grow_dev_page to do the same as __page_symlink calls. Retrieve the
> mask from the mapping and then remove __GFP_FS.
> 
> Signed-off-by: Christoph Lameter <clameter@....com>
> 
> ---
>  fs/buffer.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6.21-rc7/fs/buffer.c
> ===================================================================
> --- linux-2.6.21-rc7.orig/fs/buffer.c	2007-04-23 15:29:18.000000000 -0700
> +++ linux-2.6.21-rc7/fs/buffer.c	2007-04-23 15:29:43.000000000 -0700
> @@ -988,7 +988,8 @@ grow_dev_page(struct block_device *bdev,
>  	struct page *page;
>  	struct buffer_head *bh;
>  
> -	page = find_or_create_page(inode->i_mapping, index, GFP_NOFS);
> +	page = find_or_create_page(inode->i_mapping, index,
> +		mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS);
>  	if (!page)
>  		return NULL;

OK.  I hope.  the mapping_gfp_mask() here will have come from bdget()'s
mapping_set_gfp_mask(&inode->i_data, GFP_USER);  If anyone is accidentally
setting __GFP_HIGHMEM on a blockdev address_space we'll cause ghastly
explosions.  Albeit ones which were well-deserved.

We'll see how it goes.
-
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