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Re: [PATCH 2/6] xfs: don't zero partial page cache pages during O_DIRECT

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 2/6] xfs: don't zero partial page cache pages during O_DIRECT writes
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Thu, 21 Aug 2014 09:08:47 -0400
Cc: xfs@xxxxxxxxxxx, clm@xxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1408597754-13526-3-git-send-email-david@xxxxxxxxxxxxx>
References: <1408597754-13526-1-git-send-email-david@xxxxxxxxxxxxx> <1408597754-13526-3-git-send-email-david@xxxxxxxxxxxxx>
User-agent: Mutt/1.5.23 (2014-03-12)
On Thu, Aug 21, 2014 at 03:09:10PM +1000, Dave Chinner wrote:
> From: Chris Mason <clm@xxxxxx>
> 
> xfs is using truncate_pagecache_range to invalidate the page cache
> during DIO reads.  This is different from the other filesystems who
> only invalidate pages during DIO writes.
> 
> truncate_pagecache_range is meant to be used when we are freeing the
> underlying data structs from disk, so it will zero any partial
> ranges in the page.  This means a DIO read can zero out part of the
> page cache page, and it is possible the page will stay in cache.
> 
> buffered reads will find an up to date page with zeros instead of
> the data actually on disk.
> 
> This patch fixes things by using invalidate_inode_pages2_range
> instead.  It preserves the page cache invalidation, but won't zero
> any pages.
> 
> [dchinner: catch error and warn if it fails. Comment.]
> 
> cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Chris Mason <clm@xxxxxx>
> Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
> Signed-off-by: Dave Chinner <david@xxxxxxxxxxxxx>
> ---

Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>

>  fs/xfs/xfs_file.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index 076b170..827cfb2 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -296,7 +296,16 @@ xfs_file_read_iter(
>                               xfs_rw_iunlock(ip, XFS_IOLOCK_EXCL);
>                               return ret;
>                       }
> -                     truncate_pagecache_range(VFS_I(ip), pos, -1);
> +
> +                     /*
> +                      * Invalidate whole pages. This can return an error if
> +                      * we fail to invalidate a page, but this should never
> +                      * happen on XFS. Warn if it does fail.
> +                      */
> +                     ret = 
> invalidate_inode_pages2_range(VFS_I(ip)->i_mapping,
> +                                             pos >> PAGE_CACHE_SHIFT, -1);
> +                     WARN_ON_ONCE(ret);
> +                     ret = 0;
>               }
>               xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
>       }
> -- 
> 2.0.0
> 
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