From: Matthew Wilcox <willy@xxxxxxxxxxxxx>
commit 3159f943aafdbacb2f94c38fdaadabf2bbde2a14 upstream.
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@xxxxxxxxxxxxx>
Reviewed-by: Josef Bacik <jbacik@xxxxxx>
[ take the minimum subset of tagged pointer support only. ]
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
---
change log v2:
- fix tagged pointer apis to make it work properly pointed out by Matthew;
drivers/staging/erofs/utils.c | 18 +++++----------
include/linux/xarray.h | 52 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 58 insertions(+), 12 deletions(-)
diff --git a/drivers/staging/erofs/utils.c b/drivers/staging/erofs/utils.c
index 595cf90af9bb..bdee9bd09f11 100644
--- a/drivers/staging/erofs/utils.c
+++ b/drivers/staging/erofs/utils.c
@@ -35,7 +35,6 @@ static atomic_long_t erofs_global_shrink_cnt;
#ifdef CONFIG_EROFS_FS_ZIP
-/* radix_tree and the future XArray both don't use tagptr_t yet */
struct erofs_workgroup *erofs_find_workgroup(
struct super_block *sb, pgoff_t index, bool *tag)
{
@@ -47,9 +46,8 @@ struct erofs_workgroup *erofs_find_workgroup(
rcu_read_lock();
grp = radix_tree_lookup(&sbi->workstn_tree, index);
if (grp != NULL) {
- *tag = radix_tree_exceptional_entry(grp);
- grp = (void *)((unsigned long)grp &
- ~RADIX_TREE_EXCEPTIONAL_ENTRY);
+ *tag = xa_pointer_tag(grp);
+ grp = xa_untag_pointer(grp);
if (erofs_workgroup_get(grp, &oldcount)) {
/* prefer to relax rcu read side */
@@ -83,9 +81,7 @@ int erofs_register_workgroup(struct super_block *sb,
sbi = EROFS_SB(sb);
erofs_workstn_lock(sbi);
- if (tag)
- grp = (void *)((unsigned long)grp |
- 1UL << RADIX_TREE_EXCEPTIONAL_SHIFT);
+ grp = xa_tag_pointer(grp, tag);
err = radix_tree_insert(&sbi->workstn_tree,
grp->index, grp);
@@ -131,9 +127,7 @@ unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
for (i = 0; i < found; ++i) {
int cnt;
- struct erofs_workgroup *grp = (void *)
- ((unsigned long)batch[i] &
- ~RADIX_TREE_EXCEPTIONAL_ENTRY);
+ struct erofs_workgroup *grp = xa_untag_pointer(batch[i]);
first_index = grp->index + 1;
@@ -150,8 +144,8 @@ unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
#endif
continue;
- if (radix_tree_delete(&sbi->workstn_tree,
- grp->index) != grp) {
+ if (xa_untag_pointer(radix_tree_delete(&sbi->workstn_tree,
+ grp->index)) != grp) {
#ifdef EROFS_FS_HAS_MANAGED_CACHE
skip:
erofs_workgroup_unfreeze(grp, 1);
diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 2dfc8006fe64..51ae9779d08b 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -9,6 +9,58 @@
#include <linux/spinlock.h>
+/**
+ * xa_tag_pointer() - Create an XArray entry for a tagged pointer.
+ * @p: Plain pointer.
+ * @tag: Tag value (0 or 1).
+ *
+ * If the user of the XArray prefers, they can tag their pointers instead
+ * of storing value entries. Two tags are available (0 and 1).
+ * These are distinct from the xa_mark_t as they are not replicated up
+ * through the array and cannot be searched for.
+ *
+ * Context: Any context.
+ * Return: An XArray entry.
+ */
+static inline void *xa_tag_pointer(void *p, unsigned long tag)
+{
+ if (__builtin_constant_p(tag))
+ BUILD_BUG_ON(tag > 1);
+ else
+ BUG_ON(tag > 1);
+ return (void *)((unsigned long)p | (tag << 1));
+}
+
+/**
+ * xa_untag_pointer() - Turn an XArray entry into a plain pointer.
+ * @entry: XArray entry.
+ *
+ * If you have stored a tagged pointer in the XArray, call this function
+ * to get the untagged version of the pointer.
+ *
+ * Context: Any context.
+ * Return: A pointer.
+ */
+static inline void *xa_untag_pointer(void *entry)
+{
+ return (void *)((unsigned long)entry & ~3UL);
+}
+
+/**
+ * xa_pointer_tag() - Get the tag stored in an XArray entry.
+ * @entry: XArray entry.
+ *
+ * If you have stored a tagged pointer in the XArray, call this function
+ * to get the tag of that pointer.
+ *
+ * Context: Any context.
+ * Return: A tag.
+ */
+static inline unsigned int xa_pointer_tag(void *entry)
+{
+ return ((unsigned long)entry & 3UL) >> 1;
+}
+
#define xa_trylock(xa) spin_trylock(&(xa)->xa_lock)
#define xa_lock(xa) spin_lock(&(xa)->xa_lock)
#define xa_unlock(xa) spin_unlock(&(xa)->xa_lock)
--
2.14.5
