On Wed 03-08-16 09:40:26, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> When we do DAX IO, we try to invalidate the entire page cache held
> on the file. This is incorrect as it will trash the entire mapping
> tree that now tracks dirty state in exceptional entries in the radix
> tree slots.
>
> What we are trying to do is remove cached pages (e.g from reads
> into holes) that sit in the radix tree over the range we are about
> to write to. Hence we should just limit the invalidation to the
> range we are about to overwrite.
The patch looks good. Just one comment below.
>
> Reported-by: Jan Kara <jack@xxxxxxx>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/xfs/xfs_file.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
> index ed95e5b..e612a02 100644
> --- a/fs/xfs/xfs_file.c
> +++ b/fs/xfs/xfs_file.c
> @@ -741,9 +741,20 @@ xfs_file_dax_write(
> * page is inserted into the pagecache when we have to serve a write
> * fault on a hole. It should never be dirtied and can simply be
> * dropped from the pagecache once we get real data for the page.
> + *
> + * XXX: This is racy against mmap, and there's nothing we can do about
> + * it. dax_do_io() should really do this invalidation internally as
> + * it will know if we've allocated over a holei for this specific IO and
> + * if so it needs to update the mapping tree and invalidate existing
> + * PTEs over the newly allocated range. Remove this invalidation when
> + * dax_do_io() is fixed up.
And would it be OK for XFS if dax_do_io() actually invalidated page cache /
PTEs under just XFS_IOLOCK_SHARED? Because currently you seem to be careful
to call invalidate_inode_pages2() only when holding the lock exclusively
and then demote it to a shared one when calling dax_do_io().
Honza
> */
> if (mapping->nrpages) {
> - ret = invalidate_inode_pages2(mapping);
> + loff_t end = iocb->ki_pos + iov_iter_count(from) - 1;
> +
> + ret = invalidate_inode_pages2_range(mapping,
> + iocb->ki_pos >> PAGE_SHIFT,
> + end >> PAGE_SHIFT);
> WARN_ON_ONCE(ret);
> }
>
> --
> 2.8.0.rc3
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
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