[PATCH v4 3/4] lib/xarray: introduce a new helper xas_get_order

Kairui Song
2024-04-16T07:17:53Z

It can be used after xas_load to check the order of loaded entries.
Compared to xa_get_order, it saves an XA_STATE and avoid a rewalk.

Added new test for xas_get_order, to make the test work, we have to
export xas_get_order with EXPORT_SYMBOL_GPL.

Also fix a sparse warning by checking the slot value with xa_entry
instead of accessing it directly, as suggested by Matthew Wilcox.

Signed-off-by: Kairui Song <kasong@tencent.com>
---
include/linux/xarray.h | 6 ++++++
lib/test_xarray.c | 34 +++++++++++++++++++++++++++++
lib/xarray.c | 49 ++++++++++++++++++++++++++----------------
3 files changed, 71 insertions(+), 18 deletions(-)

diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index cb571dfcf4b1..d9d479334c9e 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -1548,6 +1548,7 @@ void xas_create_range(struct xa_state *);

#ifdef CONFIG_XARRAY_MULTI
int xa_get_order(struct xarray *, unsigned long index);
+int xas_get_order(struct xa_state *xas);
void xas_split(struct xa_state *, void *entry, unsigned int order);
void xas_split_alloc(struct xa_state *, void *entry, unsigned int order, gfp_t);
#else
@@ -1556,6 +1557,11 @@ static inline int xa_get_order(struct xarray *xa, unsigned long index)
return 0;
}

+static inline int xas_get_order(struct xa_state *xas)
+{
+ return 0;
+}
+
static inline void xas_split(struct xa_state *xas, void *entry,
unsigned int order)
{
diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index ebe2af2e072d..0efde8f93490 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -1984,6 +1984,39 @@ static noinline void check_get_order(struct xarray *xa)
}
}

+static noinline void check_xas_get_order(struct xarray *xa)
+{
+ XA_STATE(xas, xa, 0);
+
+ unsigned int max_order = IS_ENABLED(CONFIG_XARRAY_MULTI) ? 20 : 1;
+ unsigned int order;
+ unsigned long i, j;
+
+ for (order = 0; order < max_order; order++) {
+ for (i = 0; i < 10; i++) {
+ xas_set_order(&xas, i << order, order);
+ do {
+ xas_lock(&xas);
+ xas_store(&xas, xa_mk_value(i));
+ xas_unlock(&xas);
+ } while (xas_nomem(&xas, GFP_KERNEL));
+
+ for (j = i << order; j < (i + 1) << order; j++) {
+ xas_set_order(&xas, j, 0);
+ rcu_read_lock();
+ xas_load(&xas);
+ XA_BUG_ON(xa, xas_get_order(&xas) != order);
+ rcu_read_unlock();
+ }
+
+ xas_lock(&xas);
+ xas_set_order(&xas, i << order, order);
+ xas_store(&xas, NULL);
+ xas_unlock(&xas);
+ }
+ }
+}
+
static noinline void check_destroy(struct xarray *xa)
{
unsigned long index;
@@ -2035,6 +2068,7 @@ static int xarray_checks(void)
check_multi_store(&array);
check_multi_store_advanced(&array);
check_get_order(&array);
+ check_xas_get_order(&array);
check_xa_alloc();
check_find(&array);
check_find_entry(&array);
diff --git a/lib/xarray.c b/lib/xarray.c
index 39f07bfc4dcc..da79128ad754 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1750,39 +1750,52 @@ void *xa_store_range(struct xarray *xa, unsigned long first,
EXPORT_SYMBOL(xa_store_range);

/**
- * xa_get_order() - Get the order of an entry.
- * @xa: XArray.
- * @index: Index of the entry.
+ * xas_get_order() - Get the order of an entry.
+ * @xas: XArray operation state.
+ *
+ * Called after xas_load, the xas should not be in an error state.
*
* Return: A number between 0 and 63 indicating the order of the entry.
*/
-int xa_get_order(struct xarray *xa, unsigned long index)
+int xas_get_order(struct xa_state *xas)
{
- XA_STATE(xas, xa, index);
- void *entry;
int order = 0;

- rcu_read_lock();
- entry = xas_load(&xas);
-
- if (!entry)
- goto unlock;
-
- if (!xas.xa_node)
- goto unlock;
+ if (!xas->xa_node)
+ return 0;

for (;;) {
- unsigned int slot = xas.xa_offset + (1 << order);
+ unsigned int slot = xas->xa_offset + (1 << order);

if (slot >= XA_CHUNK_SIZE)
break;
- if (!xa_is_sibling(xas.xa_node->slots[slot]))
+ if (!xa_is_sibling(xa_entry(xas->xa, xas->xa_node, slot)))
break;
order++;
}

- order += xas.xa_node->shift;
-unlock:
+ order += xas->xa_node->shift;
+ return order;
+}
+EXPORT_SYMBOL_GPL(xas_get_order);
+
+/**
+ * xa_get_order() - Get the order of an entry.
+ * @xa: XArray.
+ * @index: Index of the entry.
+ *
+ * Return: A number between 0 and 63 indicating the order of the entry.
+ */
+int xa_get_order(struct xarray *xa, unsigned long index)
+{
+ XA_STATE(xas, xa, index);
+ int order = 0;
+ void *entry;
+
+ rcu_read_lock();
+ entry = xas_load(&xas);
+ if (entry)
+ order = xas_get_order(&xas);
rcu_read_unlock();

return order;
--
2.44.0