radix-tree: add gang_lookup_slot, gang_lookup_slot_tag

Introduce gang_lookup_slot() and gang_lookup_slot_tag() functions, which
are used by lockless pagecache.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 155 insertions, 23 deletions

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 56ec21a7f73d..9c4f1ffa2864 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -359,18 +359,17 @@ EXPORT_SYMBOL(radix_tree_insert);
  *      Returns:  the slot corresponding to the position @index in the
  *      radix tree @root. This is useful for update-if-exists operations.
  *
- *      This function cannot be called under rcu_read_lock, it must be
- *      excluded from writers, as must the returned slot for subsequent
- *      use by radix_tree_deref_slot() and radix_tree_replace slot.
- *      Caller must hold tree write locked across slot lookup and
- *      replace.
+ *      This function can be called under rcu_read_lock iff the slot is not
+ *      modified by radix_tree_replace_slot, otherwise it must be called
+ *      exclusive from other writers. Any dereference of the slot must be done
+ *      using radix_tree_deref_slot.
  */
 void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
 {
         unsigned int height, shift;
         struct radix_tree_node *node, **slot;
 
-        node = root->rnode;
+        node = rcu_dereference(root->rnode);
         if (node == NULL)
                 return NULL;
 
@@ -390,7 +389,7 @@ void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
         do {
                 slot = (struct radix_tree_node **)
                         (node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK));
-                node = *slot;
+                node = rcu_dereference(*slot);
                 if (node == NULL)
                         return NULL;
 
@@ -667,7 +666,7 @@ unsigned long radix_tree_next_hole(struct radix_tree_root *root,
 EXPORT_SYMBOL(radix_tree_next_hole);
 
 static unsigned int
-__lookup(struct radix_tree_node *slot, void **results, unsigned long index,
+__lookup(struct radix_tree_node *slot, void ***results, unsigned long index,
         unsigned int max_items, unsigned long *next_index)
 {
         unsigned int nr_found = 0;
@@ -701,11 +700,9 @@ __lookup(struct radix_tree_node *slot, void **results, unsigned long index,
 
         /* Bottom level: grab some items */
         for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++) {
-                struct radix_tree_node *node;
                 index++;
-                node = slot->slots[i];
-                if (node) {
-                        results[nr_found++] = rcu_dereference(node);
+                if (slot->slots[i]) {
+                        results[nr_found++] = &(slot->slots[i]);
                         if (nr_found == max_items)
                                 goto out;
                 }
@@ -759,13 +756,22 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 
         ret = 0;
         while (ret < max_items) {
-                unsigned int nr_found;
+                unsigned int nr_found, slots_found, i;
                 unsigned long next_index;       /* Index of next search */
 
                 if (cur_index > max_index)
                         break;
-                nr_found = __lookup(node, results + ret, cur_index,
+                slots_found = __lookup(node, (void ***)results + ret, cur_index,
                                         max_items - ret, &next_index);
+                nr_found = 0;
+                for (i = 0; i < slots_found; i++) {
+                        struct radix_tree_node *slot;
+                        slot = *(((void ***)results)[ret + i]);
+                        if (!slot)
+                                continue;
+                        results[ret + nr_found] = rcu_dereference(slot);
+                        nr_found++;
+                }
                 ret += nr_found;
                 if (next_index == 0)
                         break;
@@ -776,12 +782,71 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
 }
 EXPORT_SYMBOL(radix_tree_gang_lookup);
 
+/**
+ *      radix_tree_gang_lookup_slot - perform multiple slot lookup on radix tree
+ *      @root:          radix tree root
+ *      @results:       where the results of the lookup are placed
+ *      @first_index:   start the lookup from this key
+ *      @max_items:     place up to this many items at *results
+ *
+ *      Performs an index-ascending scan of the tree for present items.  Places
+ *      their slots at *@results and returns the number of items which were
+ *      placed at *@results.
+ *
+ *      The implementation is naive.
+ *
+ *      Like radix_tree_gang_lookup as far as RCU and locking goes. Slots must
+ *      be dereferenced with radix_tree_deref_slot, and if using only RCU
+ *      protection, radix_tree_deref_slot may fail requiring a retry.
+ */
+unsigned int
+radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
+                        unsigned long first_index, unsigned int max_items)
+{
+        unsigned long max_index;
+        struct radix_tree_node *node;
+        unsigned long cur_index = first_index;
+        unsigned int ret;
+
+        node = rcu_dereference(root->rnode);
+        if (!node)
+                return 0;
+
+        if (!radix_tree_is_indirect_ptr(node)) {
+                if (first_index > 0)
+                        return 0;
+                results[0] = (void **)&root->rnode;
+                return 1;
+        }
+        node = radix_tree_indirect_to_ptr(node);
+
+        max_index = radix_tree_maxindex(node->height);
+
+        ret = 0;
+        while (ret < max_items) {
+                unsigned int slots_found;
+                unsigned long next_index;       /* Index of next search */
+
+                if (cur_index > max_index)
+                        break;
+                slots_found = __lookup(node, results + ret, cur_index,
+                                        max_items - ret, &next_index);
+                ret += slots_found;
+                if (next_index == 0)
+                        break;
+                cur_index = next_index;
+        }
+
+        return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup_slot);
+
 /*
  * FIXME: the two tag_get()s here should use find_next_bit() instead of
  * open-coding the search.
  */
 static unsigned int
-__lookup_tag(struct radix_tree_node *slot, void **results, unsigned long index,
+__lookup_tag(struct radix_tree_node *slot, void ***results, unsigned long index,
         unsigned int max_items, unsigned long *next_index, unsigned int tag)
 {
         unsigned int nr_found = 0;
@@ -811,11 +876,9 @@ __lookup_tag(struct radix_tree_node *slot, void **results, unsigned long index,
                         unsigned long j = index & RADIX_TREE_MAP_MASK;
 
                         for ( ; j < RADIX_TREE_MAP_SIZE; j++) {
-                                struct radix_tree_node *node;
                                 index++;
                                 if (!tag_get(slot, tag, j))
                                         continue;
-                                node = slot->slots[j];
                                 /*
                                  * Even though the tag was found set, we need to
                                  * recheck that we have a non-NULL node, because
@@ -826,9 +889,8 @@ __lookup_tag(struct radix_tree_node *slot, void **results, unsigned long index,
                                  * lookup ->slots[x] without a lock (ie. can't
                                  * rely on its value remaining the same).
                                  */
-                                if (node) {
-                                        node = rcu_dereference(node);
-                                        results[nr_found++] = node;
+                                if (slot->slots[j]) {
+                                        results[nr_found++] = &(slot->slots[j]);
                                         if (nr_found == max_items)
                                                 goto out;
                                 }
@@ -887,13 +949,22 @@ radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
 
         ret = 0;
         while (ret < max_items) {
-                unsigned int nr_found;
+                unsigned int nr_found, slots_found, i;
                 unsigned long next_index;       /* Index of next search */
 
                 if (cur_index > max_index)
                         break;
-                nr_found = __lookup_tag(node, results + ret, cur_index,
-                                        max_items - ret, &next_index, tag);
+                slots_found = __lookup_tag(node, (void ***)results + ret,
+                                cur_index, max_items - ret, &next_index, tag);
+                nr_found = 0;
+                for (i = 0; i < slots_found; i++) {
+                        struct radix_tree_node *slot;
+                        slot = *(((void ***)results)[ret + i]);
+                        if (!slot)
+                                continue;
+                        results[ret + nr_found] = rcu_dereference(slot);
+                        nr_found++;
+                }
                 ret += nr_found;
                 if (next_index == 0)
                         break;
@@ -905,6 +976,67 @@ radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
 EXPORT_SYMBOL(radix_tree_gang_lookup_tag);
 
 /**
+ *      radix_tree_gang_lookup_tag_slot - perform multiple slot lookup on a
+ *                                        radix tree based on a tag
+ *      @root:          radix tree root
+ *      @results:       where the results of the lookup are placed
+ *      @first_index:   start the lookup from this key
+ *      @max_items:     place up to this many items at *results
+ *      @tag:           the tag index (< RADIX_TREE_MAX_TAGS)
+ *
+ *      Performs an index-ascending scan of the tree for present items which
+ *      have the tag indexed by @tag set.  Places the slots at *@results and
+ *      returns the number of slots which were placed at *@results.
+ */
+unsigned int
+radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
+                unsigned long first_index, unsigned int max_items,
+                unsigned int tag)
+{
+        struct radix_tree_node *node;
+        unsigned long max_index;
+        unsigned long cur_index = first_index;
+        unsigned int ret;
+
+        /* check the root's tag bit */
+        if (!root_tag_get(root, tag))
+                return 0;
+
+        node = rcu_dereference(root->rnode);
+        if (!node)
+                return 0;
+
+        if (!radix_tree_is_indirect_ptr(node)) {
+                if (first_index > 0)
+                        return 0;
+                results[0] = (void **)&root->rnode;
+                return 1;
+        }
+        node = radix_tree_indirect_to_ptr(node);
+
+        max_index = radix_tree_maxindex(node->height);
+
+        ret = 0;
+        while (ret < max_items) {
+                unsigned int slots_found;
+                unsigned long next_index;       /* Index of next search */
+
+                if (cur_index > max_index)
+                        break;
+                slots_found = __lookup_tag(node, results + ret,
+                                cur_index, max_items - ret, &next_index, tag);
+                ret += slots_found;
+                if (next_index == 0)
+                        break;
+                cur_index = next_index;
+        }
+
+        return ret;
+}
+EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);
+
+
+/**
  *      radix_tree_shrink    -    shrink height of a radix tree to minimal
  *      @root           radix tree root
  */