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/test_xarray.c b/lib/test_xarray.c
index 9d894e9..cd74f8f 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -589,64 +589,86 @@ static noinline void check_multi_store(struct xarray *xa)
#endif
}
-static DEFINE_XARRAY_ALLOC(xa0);
-
-static noinline void check_xa_alloc(void)
+static noinline void check_xa_alloc_1(struct xarray *xa, unsigned int base)
{
int i;
u32 id;
- /* An empty array should assign 0 to the first alloc */
- xa_alloc_index(&xa0, 0, GFP_KERNEL);
+ XA_BUG_ON(xa, !xa_empty(xa));
+ /* An empty array should assign %base to the first alloc */
+ xa_alloc_index(xa, base, GFP_KERNEL);
/* Erasing it should make the array empty again */
- xa_erase_index(&xa0, 0);
- XA_BUG_ON(&xa0, !xa_empty(&xa0));
+ xa_erase_index(xa, base);
+ XA_BUG_ON(xa, !xa_empty(xa));
- /* And it should assign 0 again */
- xa_alloc_index(&xa0, 0, GFP_KERNEL);
+ /* And it should assign %base again */
+ xa_alloc_index(xa, base, GFP_KERNEL);
- /* The next assigned ID should be 1 */
- xa_alloc_index(&xa0, 1, GFP_KERNEL);
- xa_erase_index(&xa0, 1);
+ /* Allocating and then erasing a lot should not lose base */
+ for (i = base + 1; i < 2 * XA_CHUNK_SIZE; i++)
+ xa_alloc_index(xa, i, GFP_KERNEL);
+ for (i = base; i < 2 * XA_CHUNK_SIZE; i++)
+ xa_erase_index(xa, i);
+ xa_alloc_index(xa, base, GFP_KERNEL);
+
+ /* Destroying the array should do the same as erasing */
+ xa_destroy(xa);
+
+ /* And it should assign %base again */
+ xa_alloc_index(xa, base, GFP_KERNEL);
+
+ /* The next assigned ID should be base+1 */
+ xa_alloc_index(xa, base + 1, GFP_KERNEL);
+ xa_erase_index(xa, base + 1);
/* Storing a value should mark it used */
- xa_store_index(&xa0, 1, GFP_KERNEL);
- xa_alloc_index(&xa0, 2, GFP_KERNEL);
+ xa_store_index(xa, base + 1, GFP_KERNEL);
+ xa_alloc_index(xa, base + 2, GFP_KERNEL);
- /* If we then erase 0, it should be free */
- xa_erase_index(&xa0, 0);
- xa_alloc_index(&xa0, 0, GFP_KERNEL);
+ /* If we then erase base, it should be free */
+ xa_erase_index(xa, base);
+ xa_alloc_index(xa, base, GFP_KERNEL);
- xa_erase_index(&xa0, 1);
- xa_erase_index(&xa0, 2);
+ xa_erase_index(xa, base + 1);
+ xa_erase_index(xa, base + 2);
for (i = 1; i < 5000; i++) {
- xa_alloc_index(&xa0, i, GFP_KERNEL);
+ xa_alloc_index(xa, base + i, GFP_KERNEL);
}
- xa_destroy(&xa0);
+ xa_destroy(xa);
+ /* Check that we fail properly at the limit of allocation */
id = 0xfffffffeU;
- XA_BUG_ON(&xa0, xa_alloc(&xa0, &id, UINT_MAX, xa_mk_index(id),
+ XA_BUG_ON(xa, xa_alloc(xa, &id, UINT_MAX, xa_mk_index(id),
GFP_KERNEL) != 0);
- XA_BUG_ON(&xa0, id != 0xfffffffeU);
- XA_BUG_ON(&xa0, xa_alloc(&xa0, &id, UINT_MAX, xa_mk_index(id),
+ XA_BUG_ON(xa, id != 0xfffffffeU);
+ XA_BUG_ON(xa, xa_alloc(xa, &id, UINT_MAX, xa_mk_index(id),
GFP_KERNEL) != 0);
- XA_BUG_ON(&xa0, id != 0xffffffffU);
- XA_BUG_ON(&xa0, xa_alloc(&xa0, &id, UINT_MAX, xa_mk_index(id),
+ XA_BUG_ON(xa, id != 0xffffffffU);
+ XA_BUG_ON(xa, xa_alloc(xa, &id, UINT_MAX, xa_mk_index(id),
GFP_KERNEL) != -ENOSPC);
- XA_BUG_ON(&xa0, id != 0xffffffffU);
- xa_destroy(&xa0);
+ XA_BUG_ON(xa, id != 0xffffffffU);
+ xa_destroy(xa);
id = 10;
- XA_BUG_ON(&xa0, xa_alloc(&xa0, &id, 5, xa_mk_index(id),
+ XA_BUG_ON(xa, xa_alloc(xa, &id, 5, xa_mk_index(id),
GFP_KERNEL) != -ENOSPC);
- XA_BUG_ON(&xa0, xa_store_index(&xa0, 3, GFP_KERNEL) != 0);
- XA_BUG_ON(&xa0, xa_alloc(&xa0, &id, 5, xa_mk_index(id),
+ XA_BUG_ON(xa, xa_store_index(xa, 3, GFP_KERNEL) != 0);
+ XA_BUG_ON(xa, xa_alloc(xa, &id, 5, xa_mk_index(id),
GFP_KERNEL) != -ENOSPC);
- xa_erase_index(&xa0, 3);
- XA_BUG_ON(&xa0, !xa_empty(&xa0));
+ xa_erase_index(xa, 3);
+ XA_BUG_ON(xa, !xa_empty(xa));
+}
+
+static DEFINE_XARRAY_ALLOC(xa0);
+static DEFINE_XARRAY_ALLOC1(xa1);
+
+static noinline void check_xa_alloc(void)
+{
+ check_xa_alloc_1(&xa0, 0);
+ check_xa_alloc_1(&xa1, 1);
}
static noinline void __check_store_iter(struct xarray *xa, unsigned long start,