xarray: Replace exceptional entries
Introduce xarray value entries and tagged pointers to replace radix
tree exceptional entries. This is a slight change in encoding to allow
the use of an extra bit (we can now store BITS_PER_LONG - 1 bits in a
value entry). It is also a change in emphasis; exceptional entries are
intimidating and different. As the comment explains, you can choose
to store values or pointers in the xarray and they are both first-class
citizens.
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Josef Bacik <jbacik@fb.com>
diff --git a/mm/readahead.c b/mm/readahead.c
index 4e63014..de65707 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -179,7 +179,7 @@ unsigned int __do_page_cache_readahead(struct address_space *mapping,
rcu_read_lock();
page = radix_tree_lookup(&mapping->i_pages, page_offset);
rcu_read_unlock();
- if (page && !radix_tree_exceptional_entry(page)) {
+ if (page && !xa_is_value(page)) {
/*
* Page already present? Kick off the current batch of
* contiguous pages before continuing with the next