From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
This iterator allows the user to efficiently walk a range of the array,
executing the loop body once for each non-NULL entry in that range.
This commit also includes xa_find() and xa_next() which are helper
functions for xa_for_each() but may also be useful in their own right.
In the xas family of functions, we also have xas_for_each(),
xas_find(), xas_next(), xas_pause() and xas_jump(). xas_pause() allows
a xas_for_each() iteration to be resumed later from the next element
and xas_jump() allows an iteration to be resumed from a specified index.
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
---
include/linux/xarray.h | 111 ++++++++++++++++++++++
lib/radix-tree.c | 4 +-
lib/xarray.c | 166 +++++++++++++++++++++++++++++++++
tools/testing/radix-tree/xarray-test.c | 91 ++++++++++++++++++
4 files changed, 370 insertions(+), 2 deletions(-)
diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index a570d7d9a252..a62baf6f1a28 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -133,6 +133,35 @@ bool xa_get_tag(struct xarray *, unsigned long index, xa_tag_t);
void *xa_set_tag(struct xarray *, unsigned long index, xa_tag_t);
void *xa_clear_tag(struct xarray *, unsigned long index, xa_tag_t);
+void *xa_find(struct xarray *xa, unsigned long *index, unsigned long max);
+void *xa_find_after(struct xarray *xa, unsigned long *index, unsigned long max);
+
+/**
+ * xa_for_each() - Iterate over a portion of an XArray.
+ * @xa: XArray.
+ * @entry: Entry retrieved from array.
+ * @index: Index of @entry.
+ * @max: Maximum index to retrieve from array.
+ *
+ * Initialise @index to the minimum index you want to retrieve from
+ * the array. During the iteration, @entry will have the value of the
+ * entry stored in @xa at @index. The iteration will skip all NULL
+ * entries in the array. You may modify @index during the
+ * iteration if you want to skip indices. It is safe to modify the
+ * array during the iteration. At the end of the iteration, @entry will
+ * be set to NULL and @index will have a value less than or equal to max.
+ *
+ * xa_for_each() is O(n.log(n)) while xas_for_each() is O(n). You have
+ * to handle your own locking with xas_for_each(), and if you have to unlock
+ * after each iteration, it will also end up being O(n.log(n)). xa_for_each()
+ * will spin if it hits a retry entry; if you intend to see retry entries,
+ * you should use the xas_for_each() iterator instead. The xas_for_each()
+ * iterator will expand into more inline code than xa_for_each().
+ */
+#define xa_for_each(xa, entry, index, max) \
+ for (entry = xa_find(xa, &index, max); entry; \
+ entry = xa_find_after(xa, &index, max))
+
#define BITS_PER_XA_VALUE (BITS_PER_LONG - 1)
/**
@@ -486,6 +515,12 @@ static inline bool xas_valid(const struct xa_state *xas)
return !xas_invalid(xas);
}
+/* True if the pointer is something other than a node */
+static inline bool xas_not_node(struct xa_node *node)
+{
+ return (unsigned long)node < 4096;
+}
+
/* True if the node represents head-of-tree, RESTART or BOUNDS */
static inline bool xas_top(struct xa_node *node)
{
@@ -514,6 +549,7 @@ static inline bool xas_retry(struct xa_state *xas, void *entry)
void *xas_load(struct xa_state *);
void *xas_store(struct xa_state *, void *entry);
void *xas_create(struct xa_state *);
+void *xas_find(struct xa_state *, unsigned long max);
bool xas_get_tag(const struct xa_state *, xa_tag_t);
void xas_set_tag(const struct xa_state *, xa_tag_t);
@@ -521,6 +557,7 @@ void xas_clear_tag(const struct xa_state *, xa_tag_t);
void xas_init_tags(const struct xa_state *);
bool xas_nomem(struct xa_state *, gfp_t);
+void xas_pause(struct xa_state *);
/**
* xas_reload() - Refetch an entry from the xarray.
@@ -590,6 +627,80 @@ static inline void xas_set_update(struct xa_state *xas, xa_update_node_t update)
xas->xa_update = update;
}
+/* Skip over any of these entries when iterating */
+static inline bool xa_iter_skip(void *entry)
+{
+ return unlikely(!entry ||
+ (xa_is_internal(entry) && entry < XA_RETRY_ENTRY));
+}
+
+/*
+ * node->shift is always 0 for the inline iterators unless we're processing
+ * a multi-index entry.
+ */
+#ifdef CONFIG_RADIX_TREE_MULTIORDER
+#define xa_node_shift(node) node->shift
+#else
+#define xa_node_shift(node) 0
+#endif
+
+/**
+ * xas_next_entry() - Advance iterator to next present entry.
+ * @xas: XArray operation state.
+ * @max: Highest index to return.
+ *
+ * xas_next_entry() is an inline function to optimise xarray traversal for
+ * speed. It is equivalent to calling xas_find(), and will call xas_find()
+ * for all the hard cases.
+ *
+ * Return: The next present entry after the one currently referred to by @xas.
+ */
+static inline void *xas_next_entry(struct xa_state *xas, unsigned long max)
+{
+ struct xa_node *node = xas->xa_node;
+ void *entry;
+
+ if (unlikely(xas_not_node(node) || xa_node_shift(node)))
+ return xas_find(xas, max);
+
+ do {
+ if (unlikely(xas->xa_index >= max))
+ return xas_find(xas, max);
+ if (unlikely(xas->xa_offset == XA_CHUNK_MASK))
+ return xas_find(xas, max);
+ xas->xa_index++;
+ xas->xa_offset++;
+ entry = xa_entry(xas->xa, node, xas->xa_offset);
+ } while (xa_iter_skip(entry));
+
+ return entry;
+}
+
+/*
+ * If iterating while holding a lock, drop the lock and reschedule
+ * every %XA_CHECK_SCHED loops.
+ */
+enum {
+ XA_CHECK_SCHED = 4096,
+};
+
+/**
+ * xas_for_each() - Iterate over a range of an XArray
+ * @xas: XArray operation state.
+ * @entry: Entry retrieved from array.
+ * @max: Maximum index to retrieve from array.
+ *
+ * The loop body will be executed for each entry present in the xarray
+ * between the current xas position and @max. @entry will be set to
+ * the entry retrieved from the xarray. It is safe to delete entries
+ * from the array in the loop body. You should hold either the RCU lock
+ * or the xa_lock while iterating. If you need to drop the lock, call
+ * xas_pause() first.
+ */
+#define xas_for_each(xas, entry, max) \
+ for (entry = xas_find(xas, max); entry; \
+ entry = xas_next_entry(xas, max))
+
/* Internal functions, mostly shared between radix-tree.c, xarray.c and idr.c */
void xas_destroy(struct xa_state *);
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index b24361a6e517..cb7cb9e96a8b 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -247,7 +247,7 @@ static inline unsigned long node_maxindex(const struct radix_tree_node *node)
return shift_maxindex(node->shift);
}
-static unsigned long next_index(unsigned long index,
+static unsigned long rnext_index(unsigned long index,
const struct radix_tree_node *node,
unsigned long offset)
{
@@ -2103,7 +2103,7 @@ void __rcu **idr_get_free(struct radix_tree_root *root,
if (!rtag_get(node, IDR_FREE, offset)) {
offset = radix_tree_find_next_bit(node, IDR_FREE,
offset + 1);
- start = next_index(start, node, offset);
+ start = rnext_index(start, node, offset);
if (start > max)
return ERR_PTR(-ENOSPC);
while (offset == RADIX_TREE_MAP_SIZE) {
diff --git a/lib/xarray.c b/lib/xarray.c
index 6625b1763123..ac4ff3daf476 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -96,6 +96,12 @@ static unsigned int get_offset(unsigned long index, struct xa_node *node)
return (index >> node->shift) & XA_CHUNK_MASK;
}
+static void xas_add(struct xa_state *xas, unsigned long val)
+{
+ xas->xa_index += (val << xas->xa_node->shift);
+ xas->xa_offset += val;
+}
+
static void *set_bounds(struct xa_state *xas)
{
xas->xa_node = XAS_BOUNDS;
@@ -757,6 +763,101 @@ void xas_init_tags(const struct xa_state *xas)
}
EXPORT_SYMBOL_GPL(xas_init_tags);
+/**
+ * xas_pause() - Pause a walk to drop a lock.
+ * @xas: XArray operation state.
+ *
+ * Some users need to pause a walk and drop the lock they're holding in
+ * order to yield to a higher priority thread or carry out an operation
+ * on an entry. Those users should call this function before they drop
+ * the lock. It resets the @xas to be suitable for the next iteration
+ * of the loop after the user has reacquired the lock. If most entries
+ * found during a walk require you to call xas_pause(), the xa_for_each()
+ * iterator may be more appropriate.
+ *
+ * Note that xas_pause() only works for forward iteration. If a user needs
+ * to pause a reverse iteration, we will need a xas_pause_rev().
+ */
+void xas_pause(struct xa_state *xas)
+{
+ struct xa_node *node = xas->xa_node;
+
+ if (xas_invalid(xas))
+ return;
+
+ if (node) {
+ unsigned int offset = xas->xa_offset;
+ while (++offset < XA_CHUNK_SIZE) {
+ if (!xa_is_sibling(xa_entry(xas->xa, node, offset)))
+ break;
+ }
+ xas->xa_index += (offset - xas->xa_offset) << node->shift;
+ } else {
+ xas->xa_index++;
+ }
+ xas->xa_node = XAS_RESTART;
+}
+EXPORT_SYMBOL_GPL(xas_pause);
+
+/**
+ * xas_find() - Find the next present entry in the XArray.
+ * @xas: XArray operation state.
+ * @max: Highest index to return.
+ *
+ * If the xas has not yet been walked to an entry, return the entry
+ * which has an index >= xas.xa_index. If it has been walked, the entry
+ * currently being pointed at has been processed, and so we move to the
+ * next entry.
+ *
+ * If no entry is found and the array is smaller than @max, the iterator
+ * is set to the smallest index not yet in the array. This allows @xas
+ * to be immediately passed to xas_create().
+ *
+ * Return: The entry, if found, otherwise NULL.
+ */
+void *xas_find(struct xa_state *xas, unsigned long max)
+{
+ void *entry;
+
+ if (xas_error(xas))
+ return NULL;
+
+ if (!xas->xa_node) {
+ xas->xa_index = 1;
+ return set_bounds(xas);
+ } else if (xas_top(xas->xa_node)) {
+ entry = xas_load(xas);
+ if (entry || xas_not_node(xas->xa_node))
+ return entry;
+ }
+
+ xas_add(xas, 1);
+
+ while (xas->xa_node && (xas->xa_index <= max)) {
+ if (unlikely(xas->xa_offset == XA_CHUNK_SIZE)) {
+ xas->xa_offset = xas->xa_node->offset + 1;
+ xas->xa_node = xa_parent(xas->xa, xas->xa_node);
+ continue;
+ }
+
+ entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
+ if (xa_is_node(entry)) {
+ xas->xa_node = xa_to_node(entry);
+ xas->xa_offset = 0;
+ continue;
+ }
+ if (!xa_iter_skip(entry))
+ return entry;
+
+ xas_add(xas, 1);
+ }
+
+ if (!xas->xa_node)
+ xas->xa_node = XAS_BOUNDS;
+ return NULL;
+}
+EXPORT_SYMBOL_GPL(xas_find);
+
/**
* __xa_init() - Initialise an empty XArray.
* @xa: XArray.
@@ -1009,6 +1110,71 @@ void *xa_clear_tag(struct xarray *xa, unsigned long index, xa_tag_t tag)
}
EXPORT_SYMBOL(xa_clear_tag);
+/**
+ * xa_find() - Search the XArray for a present entry.
+ * @xa: XArray.
+ * @indexp: Pointer to an index.
+ * @max: Maximum index to search to.
+ *
+ * Finds the entry in the xarray with the lowest index that is between
+ * *@indexp and max, inclusive. If an entry is found, updates @indexp to
+ * be the index of the pointer. This function is protected by the RCU read
+ * lock, so it may not find all entries if called in a loop. It will not
+ * return an %XA_RETRY_ENTRY; if you need to see retry entries, use xas_find().
+ *
+ * Return: The entry, if found, otherwise NULL.
+ */
+void *xa_find(struct xarray *xa, unsigned long *indexp, unsigned long max)
+{
+ XA_STATE(xas, xa, *indexp);
+ void *entry;
+
+ rcu_read_lock();
+ do {
+ entry = xas_find(&xas, max);
+ } while (xas_retry(&xas, entry));
+ rcu_read_unlock();
+
+ if (entry)
+ *indexp = xas.xa_index;
+ return entry;
+}
+EXPORT_SYMBOL(xa_find);
+
+/**
+ * xa_find_after() - Search the XArray for a present entry.
+ * @xa: XArray.
+ * @indexp: Pointer to an index.
+ * @max: Maximum index to search to.
+ *
+ * Finds the entry in @xa with the lowest index that is above *@indexp and
+ * less than or equal to @max. If an entry is found, updates @indexp to be
+ * the index of the pointer. This function is protected by the RCU read
+ * lock, so it may miss entries which are being simultaneously added. It
+ * will not return an %XA_RETRY_ENTRY; if you need to see retry entries,
+ * use xas_find().
+ *
+ * Return: The pointer, if found, otherwise NULL.
+ */
+void *xa_find_after(struct xarray *xa, unsigned long *indexp, unsigned long max)
+{
+ XA_STATE(xas, xa, *indexp + 1);
+ void *entry;
+
+ rcu_read_lock();
+ do {
+ entry = xas_find(&xas, max);
+ if (*indexp >= xas.xa_index)
+ entry = xas_next_entry(&xas, max);
+ } while (xas_retry(&xas, entry));
+ rcu_read_unlock();
+
+ if (entry)
+ *indexp = xas.xa_index;
+ return entry;
+}
+EXPORT_SYMBOL(xa_find_after);
+
#ifdef XA_DEBUG
void xa_dump_entry(void *entry, unsigned long index)
{
diff --git a/tools/testing/radix-tree/xarray-test.c b/tools/testing/radix-tree/xarray-test.c
index a9a2b6042177..cc5d0b7a1edf 100644
--- a/tools/testing/radix-tree/xarray-test.c
+++ b/tools/testing/radix-tree/xarray-test.c
@@ -36,6 +36,72 @@ void check_xa_tag(struct xarray *xa)
assert(xa_get_tag(xa, 0, XA_TAG_0) == false);
}
+/* Check that putting the xas into an error state works correctly */
+void check_xas_error(struct xarray *xa)
+{
+ XA_STATE(xas, xa, 0);
+
+ assert(xa_store(xa, 1, xa_mk_value(1), GFP_KERNEL) == 0);
+ assert(xa_load(xa, 1) == xa_mk_value(1));
+
+ assert(xas_error(&xas) == 0);
+
+ xas_set_err(&xas, -ENOTTY);
+ assert(xas_error(&xas) == -ENOTTY);
+
+ xas_set_err(&xas, -ENOSPC);
+ assert(xas_error(&xas) == -ENOSPC);
+
+ xas_set_err(&xas, -ENOMEM);
+ assert(xas_error(&xas) == -ENOMEM);
+
+ assert(xas_load(&xas) == NULL);
+ assert(xas_store(&xas, &xas) == NULL);
+ assert(xas_load(&xas) == NULL);
+
+ assert(xas.xa_index == 0);
+ assert(xas_next(&xas) == NULL);
+ assert(xas.xa_index == 0);
+
+ assert(xas_prev(&xas) == NULL);
+ assert(xas.xa_index == 0);
+
+ xas_set_err(&xas, 0);
+ assert(xas_error(&xas) == 0);
+
+ assert(xas_find(&xas, ULONG_MAX) == xa_mk_value(1));
+ assert(xas.xa_index == 1);
+ assert(xas_error(&xas) == 0);
+
+ assert(xas_find(&xas, ULONG_MAX) == NULL);
+ assert(xas.xa_index > 1);
+ assert(xas_error(&xas) == 0);
+ assert(xas.xa_node == XAS_BOUNDS);
+}
+
+void check_xas_retry(struct xarray *xa)
+{
+ XA_STATE(xas, xa, 0);
+
+ xa_store(xa, 0, xa_mk_value(0), GFP_KERNEL);
+ xa_store(xa, 1, xa_mk_value(1), GFP_KERNEL);
+
+ assert(xas_find(&xas, ULONG_MAX) == xa_mk_value(0));
+ xa_erase(xa, 1);
+ assert(xa_is_retry(xas_reload(&xas)));
+ assert(!xas_retry(&xas, NULL));
+ assert(!xas_retry(&xas, xa_mk_value(0)));
+ assert(xas_retry(&xas, XA_RETRY_ENTRY));
+ assert(xas.xa_node == XAS_RESTART);
+ assert(xas_next_entry(&xas, ULONG_MAX) == xa_mk_value(0));
+ assert(xas.xa_node == NULL);
+
+ xa_store(xa, 1, xa_mk_value(1), GFP_KERNEL);
+ assert(xa_is_internal(xas_reload(&xas)));
+ xas.xa_node = XAS_RESTART;
+ assert(xas_next_entry(&xas, ULONG_MAX) == xa_mk_value(0));
+}
+
void check_xa_load(struct xarray *xa)
{
unsigned long i, j;
@@ -134,6 +200,22 @@ void check_multi_store(struct xarray *xa)
}
}
+void check_find(struct xarray *xa)
+{
+ unsigned long index;
+ xa_store_order(xa, 12, 2, xa_mk_value(12));
+ xa_store(xa, 16, xa_mk_value(16), GFP_KERNEL);
+
+ index = 0;
+ assert(xa_find(xa, &index, ULONG_MAX) == xa_mk_value(12));
+ assert(index == 12);
+ index = 13;
+ assert(xa_find(xa, &index, ULONG_MAX) == xa_mk_value(12));
+ assert(index >= 12 && index < 16);
+ assert(xa_find_after(xa, &index, ULONG_MAX) == xa_mk_value(16));
+ assert(index == 16);
+}
+
void xarray_checks(void)
{
DEFINE_XARRAY(array);
@@ -141,6 +223,12 @@ void xarray_checks(void)
check_xa_tag(&array);
item_kill_tree(&array);
+ check_xas_error(&array);
+ item_kill_tree(&array);
+
+ check_xas_retry(&array);
+ item_kill_tree(&array);
+
check_xa_load(&array);
item_kill_tree(&array);
@@ -149,6 +237,9 @@ void xarray_checks(void)
check_multi_store(&array);
item_kill_tree(&array);
+
+ check_find(&array);
+ item_kill_tree(&array);
}
int __weak main(void)
--
2.15.0
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