XArray: Add support for 1s-based allocation
A lot of places want to allocate IDs starting at 1 instead of 0.
While the xa_alloc() API supports this, it's not very efficient if lots
of IDs are allocated, due to having to walk down to the bottom of the
tree to see if ID 1 is available, then all the way over to the next
non-allocated ID. This method marks ID 0 as being occupied which wastes
one slot in the XArray, but preserves xa_empty() as working.
Signed-off-by: Matthew Wilcox <willy@infradead.org>
diff --git a/lib/xarray.c b/lib/xarray.c
index 1b97ca5..468fb7b 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -57,6 +57,11 @@
return xa->xa_flags & XA_FLAGS_TRACK_FREE;
}
+static inline bool xa_zero_busy(const struct xarray *xa)
+{
+ return xa->xa_flags & XA_FLAGS_ZERO_BUSY;
+}
+
static inline void xa_mark_set(struct xarray *xa, xa_mark_t mark)
{
if (!(xa->xa_flags & XA_FLAGS_MARK(mark)))
@@ -432,6 +437,8 @@
break;
if (!xa_is_node(entry) && node->shift)
break;
+ if (xa_is_zero(entry) && xa_zero_busy(xa))
+ entry = NULL;
xas->xa_node = XAS_BOUNDS;
RCU_INIT_POINTER(xa->xa_head, entry);
@@ -628,6 +635,8 @@
if (xas_top(node)) {
entry = xa_head_locked(xa);
xas->xa_node = NULL;
+ if (!entry && xa_zero_busy(xa))
+ entry = XA_ZERO_ENTRY;
shift = xas_expand(xas, entry);
if (shift < 0)
return NULL;
@@ -1942,6 +1951,8 @@
entry = xa_head_locked(xa);
RCU_INIT_POINTER(xa->xa_head, NULL);
xas_init_marks(&xas);
+ if (xa_zero_busy(xa))
+ xa_mark_clear(xa, XA_FREE_MARK);
/* lockdep checks we're still holding the lock in xas_free_nodes() */
if (xa_is_node(entry))
xas_free_nodes(&xas, xa_to_node(entry));