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Subject[PATCH v3 24/33] radix-tree: Add radix_tree_split
Date
From: Matthew Wilcox <willy@linux.intel.com>

This new function splits a larger multiorder entry into smaller entries
(potentially multi-order entries). These entries are initialised to
RADIX_TREE_RETRY to ensure that RCU walkers who see this state aren't
confused. The caller should then call radix_tree_for_each_slot() and
radix_tree_replace_slot() in order to turn these retry entries into the
intended new entries. Tags are replicated from the original multiorder
entry into each new entry.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
---
include/linux/radix-tree.h | 12 +++
lib/radix-tree.c | 142 +++++++++++++++++++++++++++++++++-
tools/testing/radix-tree/multiorder.c | 64 +++++++++++++++
3 files changed, 214 insertions(+), 4 deletions(-)

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index 935293a..1f4b561 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -80,6 +80,14 @@ static inline bool radix_tree_is_internal_node(void *ptr)
#define RADIX_TREE_MAX_PATH (DIV_ROUND_UP(RADIX_TREE_INDEX_BITS, \
RADIX_TREE_MAP_SHIFT))

+/*
+ * @count is the count of every non-NULL element in the ->slots array
+ * whether that is an exceptional entry, a retry entry, a user pointer,
+ * a sibling entry or a pointer to the next level of the tree.
+ * @exceptional is the count of every element in ->slots which is
+ * either radix_tree_exceptional_entry() or is a sibling entry for an
+ * exceptional entry.
+ */
struct radix_tree_node {
unsigned char shift; /* Bits remaining in each slot */
unsigned char offset; /* Slot offset in parent */
@@ -293,6 +301,8 @@ void __radix_tree_replace(struct radix_tree_root *root,
struct radix_tree_node *node,
void **slot, void *item,
radix_tree_update_node_t update_node, void *private);
+void radix_tree_iter_replace(struct radix_tree_root *,
+ const struct radix_tree_iter *, void **slot, void *item);
void radix_tree_replace_slot(struct radix_tree_root *root,
void **slot, void *item);
void __radix_tree_delete_node(struct radix_tree_root *root,
@@ -335,6 +345,8 @@ static inline void radix_tree_preload_end(void)
preempt_enable();
}

+int radix_tree_split(struct radix_tree_root *, unsigned long index,
+ unsigned new_order);
int radix_tree_join(struct radix_tree_root *, unsigned long index,
unsigned new_order, void *);

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 257ad9d..704201b 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -22,6 +22,7 @@
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

+#include <linux/cpu.h>
#include <linux/errno.h>
#include <linux/init.h>
#include <linux/kernel.h>
@@ -757,7 +758,10 @@ static inline int insert_entries(struct radix_tree_node *node, void **slot,
unsigned i, n, tag, offset, tags = 0;

if (node) {
- n = 1 << (order - node->shift);
+ if (order > node->shift)
+ n = 1 << (order - node->shift);
+ else
+ n = 1;
offset = get_slot_offset(node, slot);
} else {
n = 1;
@@ -796,7 +800,8 @@ static inline int insert_entries(struct radix_tree_node *node, void **slot,
tag_set(node, tag, offset);
}
if (radix_tree_is_internal_node(old) &&
- !is_sibling_entry(node, old))
+ !is_sibling_entry(node, old) &&
+ (old != RADIX_TREE_RETRY))
radix_tree_free_nodes(old);
if (radix_tree_exceptional_entry(old))
node->exceptional--;
@@ -1020,7 +1025,8 @@ void __radix_tree_replace(struct radix_tree_root *root,
* NOTE: This cannot be used to switch between non-entries (empty slots),
* regular entries, and exceptional entries, as that requires accounting
* inside the radix tree node. When switching from one type of entry or
- * deleting, use __radix_tree_lookup() and __radix_tree_replace().
+ * deleting, use __radix_tree_lookup() and __radix_tree_replace() or
+ * radix_tree_iter_replace().
*/
void radix_tree_replace_slot(struct radix_tree_root *root,
void **slot, void *item)
@@ -1028,6 +1034,21 @@ void radix_tree_replace_slot(struct radix_tree_root *root,
replace_slot(root, NULL, slot, item, true);
}

+/**
+ * radix_tree_iter_replace - replace item in a slot
+ * @root: radix tree root
+ * @slot: pointer to slot
+ * @item: new item to store in the slot.
+ *
+ * For use with radix_tree_split() and radix_tree_for_each_slot().
+ * Caller must hold tree write locked across split and replacement.
+ */
+void radix_tree_iter_replace(struct radix_tree_root *root,
+ const struct radix_tree_iter *iter, void **slot, void *item)
+{
+ __radix_tree_replace(root, iter->node, slot, item, NULL, NULL);
+}
+
#ifdef CONFIG_RADIX_TREE_MULTIORDER
/**
* radix_tree_join - replace multiple entries with one multiorder entry
@@ -1060,6 +1081,117 @@ int radix_tree_join(struct radix_tree_root *root, unsigned long index,

return error;
}
+
+/**
+ * radix_tree_split - Split an entry into smaller entries
+ * @root: radix tree root
+ * @index: An index within the large entry
+ * @order: Order of new entries
+ *
+ * Call this function as the first step in replacing a multiorder entry
+ * with several entries of lower order. After this function returns,
+ * loop over the relevant portion of the tree using radix_tree_for_each_slot()
+ * and call radix_tree_iter_replace() to set up each new entry.
+ *
+ * The tags from this entry are replicated to all the new entries.
+ *
+ * The radix tree should be locked against modification during the entire
+ * replacement operation. Lock-free lookups will see RADIX_TREE_RETRY which
+ * should prompt RCU walkers to restart the lookup from the root.
+ */
+int radix_tree_split(struct radix_tree_root *root, unsigned long index,
+ unsigned order)
+{
+ struct radix_tree_node *parent, *node, *child;
+ void **slot;
+ unsigned int offset, end;
+ unsigned n, tag, tags = 0;
+
+ if (!__radix_tree_lookup(root, index, &parent, &slot))
+ return -ENOENT;
+ if (!parent)
+ return -ENOENT;
+
+ offset = get_slot_offset(parent, slot);
+
+ for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+ if (tag_get(parent, tag, offset))
+ tags |= 1 << tag;
+
+ for (end = offset + 1; end < RADIX_TREE_MAP_SIZE; end++) {
+ if (!is_sibling_entry(parent, parent->slots[end]))
+ break;
+ for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+ if (tags & (1 << tag))
+ tag_set(parent, tag, end);
+ /* rcu_assign_pointer ensures tags are set before RETRY */
+ rcu_assign_pointer(parent->slots[end], RADIX_TREE_RETRY);
+ }
+ rcu_assign_pointer(parent->slots[offset], RADIX_TREE_RETRY);
+ parent->exceptional -= (end - offset);
+
+ if (order == parent->shift)
+ return 0;
+ if (order > parent->shift) {
+ while (offset < end)
+ offset += insert_entries(parent, &parent->slots[offset],
+ RADIX_TREE_RETRY, order, true);
+ return 0;
+ }
+
+ node = parent;
+
+ for (;;) {
+ if (node->shift > order) {
+ child = radix_tree_node_alloc(root);
+ if (!child)
+ goto nomem;
+ child->shift = node->shift - RADIX_TREE_MAP_SHIFT;
+ child->offset = offset;
+ child->count = 0;
+ child->parent = node;
+ if (node != parent) {
+ node->count++;
+ node->slots[offset] = node_to_entry(child);
+ for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+ if (tags & (1 << tag))
+ tag_set(node, tag, offset);
+ }
+
+ node = child;
+ offset = 0;
+ continue;
+ }
+
+ n = insert_entries(node, &node->slots[offset],
+ RADIX_TREE_RETRY, order, false);
+ BUG_ON(n > RADIX_TREE_MAP_SIZE);
+
+ for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++)
+ if (tags & (1 << tag))
+ tag_set(node, tag, offset);
+ offset += n;
+
+ while (offset == RADIX_TREE_MAP_SIZE) {
+ if (node == parent)
+ break;
+ offset = node->offset;
+ child = node;
+ node = node->parent;
+ rcu_assign_pointer(node->slots[offset],
+ node_to_entry(child));
+ offset++;
+ }
+ if ((node == parent) && (offset == end))
+ return 0;
+ }
+
+ nomem:
+ /* Shouldn't happen; did user forget to preload? */
+ /* TODO: free all the allocated nodes */
+ WARN_ON(1);
+ return -ENOMEM;
+}
#endif

/**
@@ -1440,8 +1572,10 @@ void **radix_tree_next_chunk(struct radix_tree_root *root,
child = rcu_dereference_raw(node->slots[offset]);
}

- if ((child == NULL) || (child == RADIX_TREE_RETRY))
+ if (!child)
goto restart;
+ if (child == RADIX_TREE_RETRY)
+ break;
} while (radix_tree_is_internal_node(child));

/* Update the iterator state */
diff --git a/tools/testing/radix-tree/multiorder.c b/tools/testing/radix-tree/multiorder.c
index c9f656c..fa6effe 100644
--- a/tools/testing/radix-tree/multiorder.c
+++ b/tools/testing/radix-tree/multiorder.c
@@ -389,6 +389,69 @@ static void multiorder_join(void)
}
}

+static void __multiorder_split(int old_order, int new_order)
+{
+ RADIX_TREE(tree, GFP_KERNEL);
+ void **slot;
+ struct radix_tree_iter iter;
+ struct radix_tree_node *node;
+ void *item;
+
+ item_insert_order(&tree, 0, old_order);
+ radix_tree_tag_set(&tree, 0, 2);
+ radix_tree_split(&tree, 0, new_order);
+ radix_tree_for_each_slot(slot, &tree, &iter, 0) {
+ radix_tree_iter_replace(&tree, &iter, slot,
+ item_create(iter.index, new_order));
+ }
+
+ item_kill_tree(&tree);
+
+ __radix_tree_insert(&tree, 0, old_order, (void *)0x12);
+
+ item = __radix_tree_lookup(&tree, 0, &node, NULL);
+ assert(item == (void *)0x12);
+ assert(node->exceptional > 0);
+
+ radix_tree_split(&tree, 0, new_order);
+ radix_tree_for_each_slot(slot, &tree, &iter, 0) {
+ radix_tree_iter_replace(&tree, &iter, slot,
+ item_create(iter.index, new_order));
+ }
+
+ item = __radix_tree_lookup(&tree, 0, &node, NULL);
+ assert(item != (void *)0x12);
+ assert(node->exceptional == 0);
+
+ item_kill_tree(&tree);
+
+ __radix_tree_insert(&tree, 0, old_order, (void *)0x12);
+
+ item = __radix_tree_lookup(&tree, 0, &node, NULL);
+ assert(item == (void *)0x12);
+ assert(node->exceptional > 0);
+
+ radix_tree_split(&tree, 0, new_order);
+ radix_tree_for_each_slot(slot, &tree, &iter, 0) {
+ radix_tree_iter_replace(&tree, &iter, slot, (void *)0x16);
+ }
+
+ item = __radix_tree_lookup(&tree, 0, &node, NULL);
+ assert(item == (void *)0x16);
+ assert(node->exceptional > 0);
+
+ item_kill_tree(&tree);
+}
+
+static void multiorder_split(void)
+{
+ int i, j;
+
+ for (i = 9; i < 19; i++)
+ for (j = 0; j < i; j++)
+ __multiorder_split(i, j);
+}
+
void multiorder_checks(void)
{
int i;
@@ -407,4 +470,5 @@ void multiorder_checks(void)
multiorder_iteration();
multiorder_tagged_iteration();
multiorder_join();
+ multiorder_split();
}
--
2.10.2
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