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Subject: Re: [PATCH 4/6] nfs: Teach NFS about swap cache pages
From: Trond Myklebust <trond.myklebust@fys.uio.no>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@osdl.org>, Rik van Riel <riel@redhat.com>
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	 <20060825153751.24254.20709.sendpatchset@twins>
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Date: Fri, 25 Aug 2006 16:03:47 -0400
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On Fri, 2006-08-25 at 17:37 +0200, Peter Zijlstra wrote:
> Teach the NFS client how to treat PG_swapcache pages.
> 
> Replace all occurences of page->index and page->mapping in the NFS client
> with the new page_file_index() and page_file_mapping() functions.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
>  fs/nfs/dir.c      |    4 ++--
>  fs/nfs/file.c     |    6 +++---
>  fs/nfs/pagelist.c |    8 ++++----
>  fs/nfs/read.c     |   10 +++++-----
>  fs/nfs/write.c    |   34 +++++++++++++++++-----------------
>  5 files changed, 31 insertions(+), 31 deletions(-)

<snip>

> @@ -821,7 +821,7 @@ int nfs_updatepage(struct file *file, st
>  		unsigned int offset, unsigned int count)
>  {
>  	struct nfs_open_context *ctx = (struct nfs_open_context *)file->private_data;
> -	struct inode	*inode = page->mapping->host;
> +	struct inode	*inode = page_file_mapping(page)->host;
>  	struct nfs_page	*req;
>  	int		status = 0;
>  
> @@ -854,12 +854,12 @@ int nfs_updatepage(struct file *file, st
>  		offset = 0;
>  		if (unlikely(end_offs < 0)) {
>  			/* Do nothing */
> -		} else if (page->index == end_index) {
> +		} else if (page_file_index(page) == end_index) {

Is this necessary? When will we ever call nfs_updatepage() with a swap
page? AFAICS, the swap stuff always uses page dirtying and (ugh)
writepage().

>  			unsigned int pglen;
>  			pglen = (unsigned int)(end_offs & (PAGE_CACHE_SIZE-1)) + 1;
>  			if (count < pglen)
>  				count = pglen;
> -		} else if (page->index < end_index)
> +		} else if (page_file_index(page) < end_index)
>  			count = PAGE_CACHE_SIZE;
>  	}
>  
> Index: linux-2.6/fs/nfs/dir.c
> ===================================================================
> --- linux-2.6.orig/fs/nfs/dir.c
> +++ linux-2.6/fs/nfs/dir.c
> @@ -177,7 +177,7 @@ int nfs_readdir_filler(nfs_readdir_descr
>  
>  	dfprintk(DIRCACHE, "NFS: %s: reading cookie %Lu into page %lu\n",
>  			__FUNCTION__, (long long)desc->entry->cookie,
> -			page->index);
> +			page_file_index(page));
>  
>   again:
>  	timestamp = jiffies;
> @@ -201,7 +201,7 @@ int nfs_readdir_filler(nfs_readdir_descr
>  	 * Note: assumes we have exclusive access to this mapping either
>  	 *	 through inode->i_mutex or some other mechanism.
>  	 */
> -	if (page->index == 0)
> +	if (page_file_index(page) == 0)
>  		invalidate_inode_pages2_range(inode->i_mapping, PAGE_CACHE_SIZE, -1);
>  	unlock_page(page);
>  	return 0;

Why are we worried about the possibility of NFS readdir pages being swap
pages?

Cheers,
  Trond

-
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