On Tue 17-11-15 12:16:14, Dan Williams wrote:
> Currently dax mappings survive block_device shutdown. While page cache
> pages are permitted to be read/written after the block_device is torn
> down this is not acceptable in the dax case as all media access must end
> when the device is disabled. The pfn backing a dax mapping is permitted
> to be invalidated after bdev shutdown and this is indeed the case with
> brd.
>
> When a dax capable block_device driver calls del_gendisk() in its
> shutdown path, or a filesystem evicts an inode it needs to ensure that
> all the pfns that had been mapped via bdev_direct_access() are unmapped.
> This is different than the pagecache backed case where
> truncate_inode_pages() is sufficient to end I/O to pages mapped to a
> dying inode.
>
> Since dax bypasses the page cache we need to unmap in addition to
> truncating pages. Also, since dax mappings are not accounted in the
> mapping radix we uncoditionally truncate all inodes with the S_DAX flag.
> Likely when we add support for dynamic dax enable/disable control we'll
> have infrastructure to detect if the inode is unmapped and can skip the
> truncate.
>
> Cc: <[email protected]>
> Cc: Jan Kara <[email protected]>
> Cc: Dave Chinner <[email protected]>
> Cc: Matthew Wilcox <[email protected]>
> Cc: Ross Zwisler <[email protected]>
> Signed-off-by: Dan Williams <[email protected]>
> ---
> fs/inode.c | 27 +++++++++++++++++++++++++++
> mm/truncate.c | 13 +++++++++++--
> 2 files changed, 38 insertions(+), 2 deletions(-)
...
> @@ -433,7 +434,15 @@ void truncate_inode_pages_final(struct address_space
> *mapping)
> spin_lock_irq(&mapping->tree_lock);
> spin_unlock_irq(&mapping->tree_lock);
>
> - truncate_inode_pages(mapping, 0);
> + /*
> + * In the case of DAX we also need to unmap the inode
> + * since the pfn backing the mapping may be invalidated
> + * after this returns
> + */
> + if (IS_DAX(inode))
> + truncate_pagecache(inode, 0);
> + else
> + truncate_inode_pages(mapping, 0);
> }
Hum, I don't get this. truncate_inode_pages_final() gets called when inode
has no more users. So there are no mappings of the inode. So how could
truncate_pagecache() possibly make a difference?
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
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