tree 4e0fee97bdc25e76f7a786e1049a9aab6208d518
parent 78a9be0a0a3367b94af242632c525d22b26f1a87
author Matthew Wilcox <willy@linux.intel.com> 1463789034 -0700
committer Linus Torvalds <torvalds@linux-foundation.org> 1463792310 -0700

radix-tree: free up the bottom bit of exceptional entries for reuse

We are guaranteed that pointers to radix_tree_nodes always have the
bottom two bits clear (because they come from a slab cache, and slab
caches have a minimum alignment of sizeof(void *)), so we can redefine
'radix_tree_is_internal_node' to only return true if the bottom two bits
have value '01'.  This frees up one quarter of the potential values for
use by the user.

Idea from Neil Brown.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Suggested-by: Neil Brown <neilb@suse.de>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jan Kara <jack@suse.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>