path: root/lib/radix-tree.c
diff options
authorHugh Dickins <hughd@google.com>2011-08-03 16:21:18 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2011-08-03 14:25:22 -1000
commit6328650bb4d854a7dc1498d1c0048b838b0d340c (patch)
tree0e265dc86f7c4451647c1e227843cdd1530f9651 /lib/radix-tree.c
parent70d327198a434edb95b3d858bc8010b8add28e3e (diff)
radix_tree: exceptional entries and indices
A patchset to extend tmpfs to MAX_LFS_FILESIZE by abandoning its peculiar swap vector, instead keeping a file's swap entries in the same radix tree as its struct page pointers: thus saving memory, and simplifying its code and locking. This patch: The radix_tree is used by several subsystems for different purposes. A major use is to store the struct page pointers of a file's pagecache for memory management. But what if mm wanted to store something other than page pointers there too? The low bit of a radix_tree entry is already used to denote an indirect pointer, for internal use, and the unlikely radix_tree_deref_retry() case. Define the next bit as denoting an exceptional entry, and supply inline functions radix_tree_exception() to return non-0 in either unlikely case, and radix_tree_exceptional_entry() to return non-0 in the second case. If a subsystem already uses radix_tree with that bit set, no problem: it does not affect internal workings at all, but is defined for the convenience of those storing well-aligned pointers in the radix_tree. The radix_tree_gang_lookups have an implicit assumption that the caller can deduce the offset of each entry returned e.g. by the page->index of a struct page. But that may not be feasible for some kinds of item to be stored there. radix_tree_gang_lookup_slot() allow for an optional indices argument, output array in which to return those offsets. The same could be added to other radix_tree_gang_lookups, but for now keep it to the only one for which we need it. Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/radix-tree.c')
1 files changed, 19 insertions, 10 deletions
diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 7ea2e033d71..348eaefbed7 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -823,8 +823,8 @@ unsigned long radix_tree_prev_hole(struct radix_tree_root *root,
static unsigned int
-__lookup(struct radix_tree_node *slot, void ***results, unsigned long index,
- unsigned int max_items, unsigned long *next_index)
+__lookup(struct radix_tree_node *slot, void ***results, unsigned long *indices,
+ unsigned long index, unsigned int max_items, unsigned long *next_index)
unsigned int nr_found = 0;
unsigned int shift, height;
@@ -857,12 +857,16 @@ __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++) {
- index++;
if (slot->slots[i]) {
- results[nr_found++] = &(slot->slots[i]);
- if (nr_found == max_items)
+ results[nr_found] = &(slot->slots[i]);
+ if (indices)
+ indices[nr_found] = index;
+ if (++nr_found == max_items) {
+ index++;
goto out;
+ }
+ index++;
*next_index = index;
@@ -918,8 +922,8 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
if (cur_index > max_index)
- slots_found = __lookup(node, (void ***)results + ret, cur_index,
- max_items - ret, &next_index);
+ slots_found = __lookup(node, (void ***)results + ret, NULL,
+ cur_index, max_items - ret, &next_index);
nr_found = 0;
for (i = 0; i < slots_found; i++) {
struct radix_tree_node *slot;
@@ -944,6 +948,7 @@ 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
+ * @indices: where their indices should be placed (but usually NULL)
* @first_index: start the lookup from this key
* @max_items: place up to this many items at *results
@@ -958,7 +963,8 @@ EXPORT_SYMBOL(radix_tree_gang_lookup);
* protection, radix_tree_deref_slot may fail requiring a retry.
unsigned int
-radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
+radix_tree_gang_lookup_slot(struct radix_tree_root *root,
+ void ***results, unsigned long *indices,
unsigned long first_index, unsigned int max_items)
unsigned long max_index;
@@ -974,6 +980,8 @@ radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
if (first_index > 0)
return 0;
results[0] = (void **)&root->rnode;
+ if (indices)
+ indices[0] = 0;
return 1;
node = indirect_to_ptr(node);
@@ -987,8 +995,9 @@ radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
if (cur_index > max_index)
- slots_found = __lookup(node, results + ret, cur_index,
- max_items - ret, &next_index);
+ slots_found = __lookup(node, results + ret,
+ indices ? indices + ret : NULL,
+ cur_index, max_items - ret, &next_index);
ret += slots_found;
if (next_index == 0)