[PATCH v2 19/29] radix-tree: add support for multi-order iterating

Matthew Wilcox
2016-04-14T14:29:52Z

From: Ross Zwisler <ross.zwisler@linux.intel.com>

This enables the macros radix_tree_for_each_slot() and friends to be
used with multi-order entries.

The way that this works is that we treat all entries in a given slots[]
array as a single chunk. If the index given to radix_tree_next_chunk()
happens to point us to a sibling entry, we will back up iter->index so
that it points to the canonical entry, and that will be the place where
we start our iteration.

As we're processing a chunk in radix_tree_next_slot(), we process
canonical entries, skip over sibling entries, and restart the chunk
lookup if we find a non-sibling indirect pointer. This drops back to
the radix_tree_next_chunk() code, which will re-walk the tree and look
for another chunk.

This allows us to properly handle multi-order entries mixed with other
entries that are at various heights in the radix tree.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
---
include/linux/radix-tree.h | 69 +++++++++++++++++++++++----
lib/radix-tree.c | 66 ++++++++++++++-----------
tools/testing/radix-tree/generated/autoconf.h | 3 ++
tools/testing/radix-tree/linux/kernel.h | 5 +-
4 files changed, 102 insertions(+), 41 deletions(-)
create mode 100644 tools/testing/radix-tree/generated/autoconf.h

diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h
index e1512a6..8558d52 100644
--- a/include/linux/radix-tree.h
+++ b/include/linux/radix-tree.h
@@ -330,8 +330,9 @@ static inline void radix_tree_preload_end(void)
* struct radix_tree_iter - radix tree iterator state
*
* @index: index of current slot
- * @next_index: next-to-last index for this chunk
+ * @next_index: one beyond the last index for this chunk
* @tags: bit-mask for tag-iterating
+ * @shift: shift for the node that holds our slots
*
* This radix tree iterator works in terms of "chunks" of slots. A chunk is a
* subinterval of slots contained within one radix tree leaf node. It is
@@ -344,8 +345,20 @@ struct radix_tree_iter {
unsigned long index;
unsigned long next_index;
unsigned long tags;
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+ unsigned int shift;
+#endif
};

+static inline unsigned int iter_shift(struct radix_tree_iter *iter)
+{
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+ return iter->shift;
+#else
+ return 0;
+#endif
+}
+
#define RADIX_TREE_ITER_TAG_MASK 0x00FF /* tag index in lower byte */
#define RADIX_TREE_ITER_TAGGED 0x0100 /* lookup tagged slots */
#define RADIX_TREE_ITER_CONTIG 0x0200 /* stop at first hole */
@@ -405,6 +418,12 @@ void **radix_tree_iter_retry(struct radix_tree_iter *iter)
return NULL;
}

+static inline unsigned long
+__radix_tree_iter_add(struct radix_tree_iter *iter, unsigned long slots)
+{
+ return iter->index + (slots << iter_shift(iter));
+}
+
/**
* radix_tree_iter_next - resume iterating when the chunk may be invalid
* @iter: iterator state
@@ -416,7 +435,7 @@ void **radix_tree_iter_retry(struct radix_tree_iter *iter)
static inline __must_check
void **radix_tree_iter_next(struct radix_tree_iter *iter)
{
- iter->next_index = iter->index + 1;
+ iter->next_index = __radix_tree_iter_add(iter, 1);
iter->tags = 0;
return NULL;
}
@@ -430,7 +449,12 @@ void **radix_tree_iter_next(struct radix_tree_iter *iter)
static __always_inline long
radix_tree_chunk_size(struct radix_tree_iter *iter)
{
- return iter->next_index - iter->index;
+ return (iter->next_index - iter->index) >> iter_shift(iter);
+}
+
+static inline void *indirect_to_ptr(void *ptr)
+{
+ return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR);
}

/**
@@ -448,24 +472,51 @@ static __always_inline void **
radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
{
if (flags & RADIX_TREE_ITER_TAGGED) {
+ void *canon = slot;
+
iter->tags >>= 1;
+ if (unlikely(!iter->tags))
+ return NULL;
+ while (IS_ENABLED(CONFIG_RADIX_TREE_MULTIORDER) &&
+ radix_tree_is_indirect_ptr(slot[1])) {
+ if (indirect_to_ptr(slot[1]) == canon) {
+ iter->tags >>= 1;
+ iter->index = __radix_tree_iter_add(iter, 1);
+ slot++;
+ continue;
+ }
+ iter->next_index = __radix_tree_iter_add(iter, 1);
+ return NULL;
+ }
if (likely(iter->tags & 1ul)) {
- iter->index++;
+ iter->index = __radix_tree_iter_add(iter, 1);
return slot + 1;
}
- if (!(flags & RADIX_TREE_ITER_CONTIG) && likely(iter->tags)) {
+ if (!(flags & RADIX_TREE_ITER_CONTIG)) {
unsigned offset = __ffs(iter->tags);

iter->tags >>= offset;
- iter->index += offset + 1;
+ iter->index = __radix_tree_iter_add(iter, offset + 1);
return slot + offset + 1;
}
} else {
- long size = radix_tree_chunk_size(iter);
+ long count = radix_tree_chunk_size(iter);
+ void *canon = slot;

- while (--size > 0) {
+ while (--count > 0) {
slot++;
- iter->index++;
+ iter->index = __radix_tree_iter_add(iter, 1);
+
+ if (IS_ENABLED(CONFIG_RADIX_TREE_MULTIORDER) &&
+ radix_tree_is_indirect_ptr(*slot)) {
+ if (indirect_to_ptr(*slot) == canon)
+ continue;
+ else {
+ iter->next_index = iter->index;
+ break;
+ }
+ }
+
if (likely(*slot))
return slot;
if (flags & RADIX_TREE_ITER_CONTIG) {
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index ff46042..a4da86e 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -75,11 +75,6 @@ static inline void *ptr_to_indirect(void *ptr)
return (void *)((unsigned long)ptr | RADIX_TREE_INDIRECT_PTR);
}

-static inline void *indirect_to_ptr(void *ptr)
-{
- return (void *)((unsigned long)ptr & ~RADIX_TREE_INDIRECT_PTR);
-}
-
#define RADIX_TREE_RETRY ptr_to_indirect(NULL)

#ifdef CONFIG_RADIX_TREE_MULTIORDER
@@ -885,6 +880,14 @@ int radix_tree_tag_get(struct radix_tree_root *root,
}
EXPORT_SYMBOL(radix_tree_tag_get);

+static inline void __set_iter_shift(struct radix_tree_iter *iter,
+ unsigned int shift)
+{
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+ iter->shift = shift;
+#endif
+}
+
/**
* radix_tree_next_chunk - find next chunk of slots for iteration
*
@@ -898,7 +901,7 @@ void **radix_tree_next_chunk(struct radix_tree_root *root,
{
unsigned shift, tag = flags & RADIX_TREE_ITER_TAG_MASK;
struct radix_tree_node *rnode, *node;
- unsigned long index, offset, height;
+ unsigned long index, offset, maxindex;

if ((flags & RADIX_TREE_ITER_TAGGED) && !root_tag_get(root, tag))
return NULL;
@@ -916,33 +919,39 @@ void **radix_tree_next_chunk(struct radix_tree_root *root,
if (!index && iter->index)
return NULL;

- rnode = rcu_dereference_raw(root->rnode);
+ restart:
+ shift = radix_tree_load_root(root, &rnode, &maxindex);
+ if (index > maxindex)
+ return NULL;
+
if (radix_tree_is_indirect_ptr(rnode)) {
rnode = indirect_to_ptr(rnode);
- } else if (rnode && !index) {
+ } else if (rnode) {
/* Single-slot tree */
- iter->index = 0;
- iter->next_index = 1;
+ iter->index = index;
+ iter->next_index = maxindex + 1;
iter->tags = 1;
+ __set_iter_shift(iter, shift);
return (void **)&root->rnode;
} else
return NULL;

-restart:
- height = rnode->path & RADIX_TREE_HEIGHT_MASK;
- shift = (height - 1) * RADIX_TREE_MAP_SHIFT;
+ shift -= RADIX_TREE_MAP_SHIFT;
offset = index >> shift;

- /* Index outside of the tree */
- if (offset >= RADIX_TREE_MAP_SIZE)
- return NULL;
-
node = rnode;
while (1) {
struct radix_tree_node *slot;
+ unsigned new_off = radix_tree_descend(node, &slot, offset);
+
+ if (new_off < offset) {
+ offset = new_off;
+ index &= ~((RADIX_TREE_MAP_SIZE << shift) - 1);
+ index |= offset << shift;
+ }
+
if ((flags & RADIX_TREE_ITER_TAGGED) ?
- !test_bit(offset, node->tags[tag]) :
- !node->slots[offset]) {
+ !tag_get(node, tag, offset) : !slot) {
/* Hole detected */
if (flags & RADIX_TREE_ITER_CONTIG)
return NULL;
@@ -954,7 +963,10 @@ restart:
offset + 1);
else
while (++offset < RADIX_TREE_MAP_SIZE) {
- if (node->slots[offset])
+ void *slot = node->slots[offset];
+ if (is_sibling_entry(node, slot))
+ continue;
+ if (slot)
break;
}
index &= ~((RADIX_TREE_MAP_SIZE << shift) - 1);
@@ -964,25 +976,23 @@ restart:
return NULL;
if (offset == RADIX_TREE_MAP_SIZE)
goto restart;
+ slot = rcu_dereference_raw(node->slots[offset]);
}

- /* This is leaf-node */
- if (!shift)
- break;
-
- slot = rcu_dereference_raw(node->slots[offset]);
- if (slot == NULL)
+ if ((slot == NULL) || (slot == RADIX_TREE_RETRY))
goto restart;
if (!radix_tree_is_indirect_ptr(slot))
break;
+
node = indirect_to_ptr(slot);
shift -= RADIX_TREE_MAP_SHIFT;
offset = (index >> shift) & RADIX_TREE_MAP_MASK;
}

/* Update the iterator state */
- iter->index = index;
- iter->next_index = (index | RADIX_TREE_MAP_MASK) + 1;
+ iter->index = index & ~((1 << shift) - 1);
+ iter->next_index = (index | ((RADIX_TREE_MAP_SIZE << shift) - 1)) + 1;
+ __set_iter_shift(iter, shift);

/* Construct iter->tags bit-mask from node->tags[tag] array */
if (flags & RADIX_TREE_ITER_TAGGED) {
diff --git a/tools/testing/radix-tree/generated/autoconf.h b/tools/testing/radix-tree/generated/autoconf.h
new file mode 100644
index 0000000..ad18cf5
--- /dev/null
+++ b/tools/testing/radix-tree/generated/autoconf.h
@@ -0,0 +1,3 @@
+#define CONFIG_RADIX_TREE_MULTIORDER 1
+#define CONFIG_SHMEM 1
+#define CONFIG_SWAP 1
diff --git a/tools/testing/radix-tree/linux/kernel.h b/tools/testing/radix-tree/linux/kernel.h
index 8ea0ed4..be98a47 100644
--- a/tools/testing/radix-tree/linux/kernel.h
+++ b/tools/testing/radix-tree/linux/kernel.h
@@ -8,10 +8,7 @@
#include <limits.h>

#include "../../include/linux/compiler.h"
-
-#define CONFIG_RADIX_TREE_MULTIORDER
-#define CONFIG_SHMEM
-#define CONFIG_SWAP
+#include "../../../include/linux/kconfig.h"

#define RADIX_TREE_MAP_SHIFT 3

--
2.8.0.rc3