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Date: Wed, 10 Jan 2007 17:23:44 +1100
From: David Chinner <dgc@sgi.com>
Subject: Re: Review: fix mapping invalidation callouts
Message-ID: <20070110062344.GR33919298@melbourne.sgi.com>
References: <20070108040309.GX33919298@melbourne.sgi.com>
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To: David Chinner <dgc@sgi.com>
Cc: xfs-dev@sgi.com, xfs@oss.sgi.com

On Mon, Jan 08, 2007 at 03:03:09PM +1100, David Chinner wrote:
> With the recent cancel_dirty_page() changes, a warning was
> added if we cancel a dirty page that is still mapped into
> the page tables.
> This happens in XFS from fs_tosspages() and fs_flushinval_pages()
> because they call truncate_inode_pages().
> 
> truncate_inode_pages() does not invalidate existing page mappings;
> it is expected taht this is called only when truncating the file
> or destroying the inode and on both these cases there can be
> no mapped ptes. However, we call this when doing direct I/O writes
> to remove pages from the page cache. As a result, we can rip
> a page from the page cache that still has mappings attached.
> 
> The correct fix is to use invalidate_inode_pages2_range() instead
> of truncate_inode_pages(). They essentially do the same thing, but
> the former also removes any pte mappings before removing the page
> from the page cache.
> 
> Comments?
> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> Principal Engineer
> SGI Australian Software Group
> 
> 
> ---
>  fs/xfs/linux-2.6/xfs_fs_subr.c |   10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> Index: 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_fs_subr.c
> ===================================================================
> --- 2.6.x-xfs-new.orig/fs/xfs/linux-2.6/xfs_fs_subr.c	2006-12-12 12:05:17.000000000 +1100
> +++ 2.6.x-xfs-new/fs/xfs/linux-2.6/xfs_fs_subr.c	2007-01-08 09:30:22.056571711 +1100
> @@ -21,6 +21,8 @@ int  fs_noerr(void) { return 0; }
>  int  fs_nosys(void) { return ENOSYS; }
>  void fs_noval(void) { return; }
>  
> +#define XFS_OFF_TO_PCSIZE(off)	\
> +	(((off) + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT)

I don't think this is right.

Assuming 4k page size, first = 2k, last = 6k will result in
invalidating page indexes 1 and 2 i.e. offset 4k -> 12k. In fact,
we want to invalidate pages 0 and 1.

IOWs, I think it should be:

+#define XFS_OFF_TO_PCINDEX(off)	((off) >> PAGE_CACHE_SHIFT)

Comments?

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group