The patch titled
Subject: radix-tree: free up the bottom bit of exceptional entries for reuse
has been added to the -mm tree. Its filename is
radix-tree-free-up-the-bottom-bit-of-exceptional-entries-for-reuse.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/radix-tree-free-up-the-bottom-bit-of-exceptional-entries-for-reuse.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/radix-tree-free-up-the-bottom-bit-of-exceptional-entries-for-reuse.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Subject: radix-tree: free up the bottom bit of exceptional entries for reuse
We are guaranteed that pointers to radix_tree_nodes always have the bottom
two bits clear (because they come from a slab cache, and slab caches have
a minimum alignment of sizeof(void *)), so we can redefine
'radix_tree_is_internal_node' to only return true if the bottom two bits
have value '01'. This frees up one quarter of the potential values for
use by the user.
Idea from Neil Brown.
Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxxxx>
Suggested-by: Neil Brown <neilb@xxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Cc: Kirill Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/radix-tree.h | 36 +++++++++++++++++++++--------------
1 file changed, 22 insertions(+), 14 deletions(-)
diff -puN include/linux/radix-tree.h~radix-tree-free-up-the-bottom-bit-of-exceptional-entries-for-reuse include/linux/radix-tree.h
--- a/include/linux/radix-tree.h~radix-tree-free-up-the-bottom-bit-of-exceptional-entries-for-reuse
+++ a/include/linux/radix-tree.h
@@ -29,28 +29,37 @@
#include <linux/rcupdate.h>
/*
- * Entries in the radix tree have the low bit set if they refer to a
- * radix_tree_node. If the low bit is clear then the entry is user data.
+ * The bottom two bits of the slot determine how the remaining bits in the
+ * slot are interpreted:
*
- * We also use the low bit to indicate that the slot will be freed in the
- * next RCU idle period, and users need to re-walk the tree to find the
- * new slot for the index that they were looking for. See the comment in
- * radix_tree_shrink() for details.
+ * 00 - data pointer
+ * 01 - internal entry
+ * 10 - exceptional entry
+ * 11 - locked exceptional entry
+ *
+ * The internal entry may be a pointer to the next level in the tree, a
+ * sibling entry, or an indicator that the entry in this slot has been moved
+ * to another location in the tree and the lookup should be restarted. While
+ * NULL fits the 'data pointer' pattern, it means that there is no entry in
+ * the tree for this index (no matter what level of the tree it is found at).
+ * This means that you cannot store NULL in the tree as a value for the index.
*/
-#define RADIX_TREE_INTERNAL_NODE 1
+#define RADIX_TREE_ENTRY_MASK 3UL
+#define RADIX_TREE_INTERNAL_NODE 1UL
/*
- * A common use of the radix tree is to store pointers to struct pages;
- * but shmem/tmpfs needs also to store swap entries in the same tree:
- * those are marked as exceptional entries to distinguish them.
+ * Most users of the radix tree store pointers but shmem/tmpfs stores swap
+ * entries in the same tree. They are marked as exceptional entries to
+ * distinguish them from pointers to struct page.
* EXCEPTIONAL_ENTRY tests the bit, EXCEPTIONAL_SHIFT shifts content past it.
*/
#define RADIX_TREE_EXCEPTIONAL_ENTRY 2
#define RADIX_TREE_EXCEPTIONAL_SHIFT 2
-static inline int radix_tree_is_internal_node(void *ptr)
+static inline bool radix_tree_is_internal_node(void *ptr)
{
- return (int)((unsigned long)ptr & RADIX_TREE_INTERNAL_NODE);
+ return ((unsigned long)ptr & RADIX_TREE_ENTRY_MASK) ==
+ RADIX_TREE_INTERNAL_NODE;
}
/*** radix-tree API starts here ***/
@@ -236,8 +245,7 @@ static inline int radix_tree_exceptional
*/
static inline int radix_tree_exception(void *arg)
{
- return unlikely((unsigned long)arg &
- (RADIX_TREE_INTERNAL_NODE | RADIX_TREE_EXCEPTIONAL_ENTRY));
+ return unlikely((unsigned long)arg & RADIX_TREE_ENTRY_MASK);
}
/**
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxxxx are
radix-tree-introduce-radix_tree_empty.patch
radix-tree-test-suite-fix-build.patch
radix-tree-test-suite-add-tests-for-radix_tree_locate_item.patch
introduce-config_radix_tree_multiorder.patch
radix-tree-add-missing-sibling-entry-functionality.patch
radix-tree-fix-sibling-entry-insertion.patch
radix-tree-fix-deleting-a-multi-order-entry-through-an-alias.patch
radix-tree-remove-restriction-on-multi-order-entries.patch
radix-tree-introduce-radix_tree_load_root.patch
radix-tree-fix-extending-the-tree-for-multi-order-entries-at-offset-0.patch
radix-tree-test-suite-start-adding-multiorder-tests.patch
radix-tree-fix-several-shrinking-bugs-with-multiorder-entries.patch
radix-tree-rewrite-__radix_tree_lookup.patch
radix-tree-fix-multiorder-bug_on-in-radix_tree_insert.patch
radix-tree-fix-radix_tree_create-for-sibling-entries.patch
radix-tree-rewrite-radix_tree_locate_item.patch
radix-tree-fix-radix_tree_range_tag_if_tagged-for-multiorder-entries.patch
radix-tree-add-copyright-statements.patch
drivers-hwspinlock-use-correct-radix-tree-api.patch
radix-tree-miscellaneous-fixes.patch
radix-tree-split-node-path-into-offset-and-height.patch
radix-tree-replace-node-height-with-node-shift.patch
radix-tree-remove-a-use-of-root-height-from-delete_node.patch
radix-tree-test-suite-remove-dependencies-on-height.patch
radix-tree-remove-root-height.patch
radix-tree-rename-indirect_ptr-to-internal_node.patch
radix-tree-rename-ptr_to_indirect-to-node_to_entry.patch
radix-tree-rename-indirect_to_ptr-to-entry_to_node.patch
radix-tree-rename-radix_tree_is_indirect_ptr.patch
radix-tree-change-naming-conventions-in-radix_tree_shrink.patch
radix-tree-tidy-up-next_chunk.patch
radix-tree-tidy-up-range_tag_if_tagged.patch
radix-tree-tidy-up-__radix_tree_create.patch
radix-tree-introduce-radix_tree_replace_clear_tags.patch
radix-tree-make-radix_tree_descend-more-useful.patch
radix-tree-free-up-the-bottom-bit-of-exceptional-entries-for-reuse.patch
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