backing_dev_info cleanups & lifetime rule fixes V2

[Jens Axboe]

On 01/14/2015 02:42 AM, Christoph Hellwig wrote:
> The first 8 patches are unchanged from the series posted a week ago and
> cleans up how we use the backing_dev_info structure in preparation for
> fixing the life time rules for it.  The most important change is to
> split the unrelated nommu mmap flags from it, but it also remove a
> backing_dev_info pointer from the address_space (and thus the inode)
> and cleans up various other minor bits.
>
> The remaining patches sort out the issues around bdi_unlink and now
> let the bdi life until it's embedding structure is freed, which must
> be equal or longer than the superblock using the bdi for writeback,
> and thus gets rid of the whole mess around reassining inodes to new
> bdis.
>
> Changes since V1:
>   - various minor documentation updates based on Feedback from Tejun

I applied this to for-3.20/bdi, only making the change (noticed by Jan) 
to kill the extra WARN_ON() in patch #11.


-- 
Jens Axboe