[v5,03/78] xarray: Add the xa_lock to the radix_tree_root

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Tue, Dec 26, 2017 at 07:43:40PM -0800, Matthew Wilcox wrote:
> On Tue, Dec 26, 2017 at 07:54:40PM +0300, Kirill A. Shutemov wrote:
> > On Fri, Dec 15, 2017 at 02:03:35PM -0800, Matthew Wilcox wrote:
> > > From: Matthew Wilcox <mawilcox@microsoft.com>
> > > 
> > > This results in no change in structure size on 64-bit x86 as it fits in
> > > the padding between the gfp_t and the void *.
> > 
> > The patch does more than described in the subject and commit message. At first
> > I was confused why do you need to touch idr here. It took few minutes to figure
> > it out.
> > 
> > Could you please add more into commit message about lockname and xa_ locking
> > interface since you introduce it here?
> 
> Sure!  How's this?
> 
>     xarray: Add the xa_lock to the radix_tree_root
>     
>     This results in no change in structure size on 64-bit x86 as it fits in
>     the padding between the gfp_t and the void *.
>     
>     Initialising the spinlock requires a name for the benefit of lockdep,
>     so RADIX_TREE_INIT() now needs to know the name of the radix tree it's
>     initialising, and so do IDR_INIT() and IDA_INIT().
>     
>     Also add the xa_lock() and xa_unlock() family of wrappers to make it
>     easier to use the lock.  If we could rely on -fplan9-extensions in
>     the compiler, we could avoid all of this syntactic sugar, but that
>     wasn't added until gcc 4.6.
> 

Looks great, thanks.