In order to use multi-index entries for huge pages in the page cache,
we need to be able to split a multi-index entry (eg if a file is
truncated in the middle of a huge page entry). This version does not
support splitting more than one level of the tree at a time. This is an
acceptable limitation for the page cache as we do not expect to support
order-12 pages in the near future.
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
Documentation/core-api/xarray.rst | 16 ++--
include/linux/xarray.h | 2 +
lib/test_xarray.c | 41 ++++++++
lib/xarray.c | 153 ++++++++++++++++++++++++++++--
4 files changed, 196 insertions(+), 16 deletions(-)
diff --git a/Documentation/core-api/xarray.rst b/Documentation/core-api/xarray.rst
index 640934b6f7b4..a137a0e6d068 100644
--- a/Documentation/core-api/xarray.rst
+++ b/Documentation/core-api/xarray.rst
@@ -475,13 +475,15 @@ or iterations will move the index to the first index in the range.
Each entry will only be returned once, no matter how many indices it
occupies.
-Using xas_next() or xas_prev() with a multi-index xa_state
-is not supported. Using either of these functions on a multi-index entry
-will reveal sibling entries; these should be skipped over by the caller.
-
-Storing ``NULL`` into any index of a multi-index entry will set the entry
-at every index to ``NULL`` and dissolve the tie. Splitting a multi-index
-entry into entries occupying smaller ranges is not yet supported.
+Using xas_next() or xas_prev() with a multi-index xa_state is not
+supported. Using either of these functions on a multi-index entry will
+reveal sibling entries; these should be skipped over by the caller.
+
+Storing ``NULL`` into any index of a multi-index entry will set the
+entry at every index to ``NULL`` and dissolve the tie. A multi-index
+entry can be split into entries occupying smaller ranges by calling
+xas_split_alloc() without the xa_lock held, followed by taking the lock
+and calling xas_split().
Functions and structures
========================
diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index b4d70e7568b2..fd4364e17632 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -1491,6 +1491,8 @@ static inline bool xas_retry(struct xa_state *xas, const void *entry)
void *xas_load(struct xa_state *);
void *xas_store(struct xa_state *, void *entry);
+void xas_split(struct xa_state *, void *entry, unsigned int order);
+void xas_split_alloc(struct xa_state *, void *entry, unsigned int order, gfp_t);
void *xas_find(struct xa_state *, unsigned long max);
void *xas_find_conflict(struct xa_state *);
diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index acf5ccba58b0..282cce959aba 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -1525,6 +1525,46 @@ static noinline void check_store_range(struct xarray *xa)
}
}
+#ifdef CONFIG_XARRAY_MULTI
+static void check_split_1(struct xarray *xa, unsigned long index,
+ unsigned int order)
+{
+ XA_STATE_ORDER(xas, xa, index, order);
+ void *entry;
+ unsigned int i = 0;
+
+ xa_store_order(xa, index, order, xa, GFP_KERNEL);
+
+ xas_split_alloc(&xas, xa, 0, GFP_KERNEL);
+ xas_lock(&xas);
+ xas_split(&xas, xa, 0);
+ xas_unlock(&xas);
+
+ xa_for_each(xa, index, entry) {
+ XA_BUG_ON(xa, entry != xa);
+ i++;
+ }
+ XA_BUG_ON(xa, i != 1 << order);
+
+ xa_destroy(xa);
+}
+
+static noinline void check_split(struct xarray *xa)
+{
+ unsigned int order;
+
+ XA_BUG_ON(xa, !xa_empty(xa));
+
+ for (order = 1; order < 2 * XA_CHUNK_SHIFT; order++) {
+ check_split_1(xa, 0, order);
+ check_split_1(xa, 1UL << order, order);
+ check_split_1(xa, 3UL << order, order);
+ }
+}
+#else
+static void check_split(struct xarray *xa) { }
+#endif
+
static void check_align_1(struct xarray *xa, char *name)
{
int i;
@@ -1730,6 +1770,7 @@ static int xarray_checks(void)
check_store_range(&array);
check_store_iter(&array);
check_align(&xa0);
+ check_split(&array);
check_workingset(&array, 0);
check_workingset(&array, 64);
diff --git a/lib/xarray.c b/lib/xarray.c
index e9e641d3c0c3..faca1ac95b0e 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -266,13 +266,15 @@ static void xa_node_free(struct xa_node *node)
*/
static void xas_destroy(struct xa_state *xas)
{
- struct xa_node *node = xas->xa_alloc;
+ struct xa_node *next, *node = xas->xa_alloc;
- if (!node)
- return;
- XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
- kmem_cache_free(radix_tree_node_cachep, node);
- xas->xa_alloc = NULL;
+ while (node) {
+ XA_NODE_BUG_ON(node, !list_empty(&node->private_list));
+ next = rcu_dereference_raw(node->parent);
+ /* XXX: need to free children */
+ kmem_cache_free(radix_tree_node_cachep, node);
+ xas->xa_alloc = node = next;
+ }
}
/**
@@ -304,6 +306,7 @@ bool xas_nomem(struct xa_state *xas, gfp_t gfp)
xas->xa_alloc = kmem_cache_alloc(radix_tree_node_cachep, gfp);
if (!xas->xa_alloc)
return false;
+ xas->xa_alloc->parent = NULL;
XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list));
xas->xa_node = XAS_RESTART;
return true;
@@ -339,6 +342,7 @@ static bool __xas_nomem(struct xa_state *xas, gfp_t gfp)
}
if (!xas->xa_alloc)
return false;
+ xas->xa_alloc->parent = NULL;
XA_NODE_BUG_ON(xas->xa_alloc, !list_empty(&xas->xa_alloc->private_list));
xas->xa_node = XAS_RESTART;
return true;
@@ -403,7 +407,7 @@ static unsigned long xas_size(const struct xa_state *xas)
/*
* Use this to calculate the maximum index that will need to be created
* in order to add the entry described by @xas. Because we cannot store a
- * multiple-index entry at index 0, the calculation is a little more complex
+ * multi-index entry at index 0, the calculation is a little more complex
* than you might expect.
*/
static unsigned long xas_max(struct xa_state *xas)
@@ -946,6 +950,137 @@ void xas_init_marks(const struct xa_state *xas)
}
EXPORT_SYMBOL_GPL(xas_init_marks);
+#ifdef CONFIG_XARRAY_MULTI
+static unsigned int node_get_marks(struct xa_node *node, unsigned int offset)
+{
+ unsigned int marks = 0;
+ xa_mark_t mark = XA_MARK_0;
+
+ for (;;) {
+ if (node_get_mark(node, offset, mark))
+ marks |= 1 << (__force unsigned int)mark;
+ if (mark == XA_MARK_MAX)
+ break;
+ mark_inc(mark);
+ }
+
+ return marks;
+}
+
+static void node_set_marks(struct xa_node *node, unsigned int offset,
+ struct xa_node *child, unsigned int marks)
+{
+ xa_mark_t mark = XA_MARK_0;
+
+ for (;;) {
+ if (marks & (1 << (__force unsigned int)mark))
+ node_set_mark(node, offset, mark);
+ if (child)
+ node_mark_all(child, mark);
+ if (mark == XA_MARK_MAX)
+ break;
+ mark_inc(mark);
+ }
+}
+
+void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order,
+ gfp_t gfp)
+{
+ unsigned int sibs = xas->xa_sibs;
+ unsigned int mask = (1 << (order % XA_CHUNK_SHIFT)) - 1;
+
+ /* XXX: no support for splitting really large entries yet */
+ if (WARN_ON(order + XA_CHUNK_SHIFT < xas->xa_shift))
+ goto nomem;
+ if (xas->xa_shift <= order)
+ return;
+
+ do {
+ unsigned int i;
+ void *sibling;
+ struct xa_node *node;
+
+ node = kmem_cache_alloc(radix_tree_node_cachep, gfp);
+ if (!node)
+ goto nomem;
+ node->array = xas->xa;
+ for (i = 0; i < XA_CHUNK_SIZE; i++) {
+ if ((i & mask) == 0) {
+ RCU_INIT_POINTER(node->slots[i], entry);
+ sibling = xa_mk_sibling(0);
+ } else {
+ RCU_INIT_POINTER(node->slots[i], sibling);
+ }
+ }
+ RCU_INIT_POINTER(node->parent, xas->xa_alloc);
+ xas->xa_alloc = node;
+ } while (sibs-- > 0);
+
+ return;
+nomem:
+ xas_destroy(xas);
+ xas_set_err(xas, -ENOMEM);
+}
+
+/**
+ * xas_split() - Split a multi-index entry into smaller entries.
+ * @xas: XArray operation state.
+ * @entry: New entry to store in the array.
+ * @order: New entry order.
+ *
+ * The value in the entry is copied to all the replacement entries.
+ *
+ * Context: Any context. The caller should hold the xa_lock.
+ */
+void xas_split(struct xa_state *xas, void *entry, unsigned int order)
+{
+ unsigned int offset, marks;
+ struct xa_node *node;
+ void *curr = xas_load(xas);
+ int values = 0;
+
+ node = xas->xa_node;
+ if (xas_top(node))
+ return;
+
+ marks = node_get_marks(node, xas->xa_offset);
+
+ offset = xas->xa_offset + xas->xa_sibs;
+ do {
+ if (order < node->shift) {
+ struct xa_node *child = xas->xa_alloc;
+
+ xas->xa_alloc = rcu_dereference_raw(child->parent);
+ child->shift = node->shift - XA_CHUNK_SHIFT;
+ child->offset = offset;
+ child->count = XA_CHUNK_SIZE;
+ child->nr_values = xa_is_value(entry) ?
+ XA_CHUNK_SIZE : 0;
+ RCU_INIT_POINTER(child->parent, node);
+ node_set_marks(node, offset, child, marks);
+ rcu_assign_pointer(node->slots[offset],
+ xa_mk_node(child));
+ if (xa_is_value(curr))
+ values--;
+ } else {
+ unsigned int canon = offset -
+ (1 << (order % XA_CHUNK_SHIFT)) + 1;
+
+ node_set_marks(node, canon, NULL, marks);
+ rcu_assign_pointer(node->slots[canon], entry);
+ while (offset > canon)
+ rcu_assign_pointer(node->slots[offset--],
+ xa_mk_sibling(canon));
+ values += (xa_is_value(entry) - xa_is_value(curr)) *
+ (1 << (order % XA_CHUNK_SHIFT));
+ }
+ } while (offset-- > xas->xa_offset);
+
+ node->nr_values += values;
+}
+EXPORT_SYMBOL_GPL(xas_split);
+#endif
+
/**
* xas_pause() - Pause a walk to drop a lock.
* @xas: XArray operation state.
@@ -1407,7 +1542,7 @@ EXPORT_SYMBOL(__xa_store);
* @gfp: Memory allocation flags.
*
* After this function returns, loads from this index will return @entry.
- * Storing into an existing multislot entry updates the entry of every index.
+ * Storing into an existing multi-index entry updates the entry of every index.
* The marks associated with @index are unaffected unless @entry is %NULL.
*
* Context: Any context. Takes and releases the xa_lock.
@@ -1549,7 +1684,7 @@ static void xas_set_range(struct xa_state *xas, unsigned long first,
*
* After this function returns, loads from any index between @first and @last,
* inclusive will return @entry.
- * Storing into an existing multislot entry updates the entry of every index.
+ * Storing into an existing multi-index entry updates the entry of every index.
* The marks associated with @index are unaffected unless @entry is %NULL.
*
* Context: Process context. Takes and releases the xa_lock. May sleep
--
2.27.0
