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radix-tree: add gang_lookup_slot, gang_lookup_slot_tag
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Introduce gang_lookup_slot() and gang_lookup_slot_tag() functions, which
are used by lockless pagecache.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Reviewed-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Nick Piggin authored and Linus Torvalds committed Jul 26, 2008
1 parent 30002ed commit 47feff2
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Showing 2 changed files with 166 additions and 24 deletions.
12 changes: 11 additions & 1 deletion include/linux/radix-tree.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -99,12 +99,15 @@ do { \
*
* The notable exceptions to this rule are the following functions:
* radix_tree_lookup
* radix_tree_lookup_slot
* radix_tree_tag_get
* radix_tree_gang_lookup
* radix_tree_gang_lookup_slot
* radix_tree_gang_lookup_tag
* radix_tree_gang_lookup_tag_slot
* radix_tree_tagged
*
* The first 4 functions are able to be called locklessly, using RCU. The
* The first 7 functions are able to be called locklessly, using RCU. The
* caller must ensure calls to these functions are made within rcu_read_lock()
* regions. Other readers (lock-free or otherwise) and modifications may be
* running concurrently.
Expand Down Expand Up @@ -159,6 +162,9 @@ void *radix_tree_delete(struct radix_tree_root *, unsigned long);
unsigned int
radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
unsigned long first_index, unsigned int max_items);
unsigned int
radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
unsigned long first_index, unsigned int max_items);
unsigned long radix_tree_next_hole(struct radix_tree_root *root,
unsigned long index, unsigned long max_scan);
int radix_tree_preload(gfp_t gfp_mask);
Expand All @@ -173,6 +179,10 @@ unsigned int
radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
unsigned long first_index, unsigned int max_items,
unsigned int tag);
unsigned int
radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
unsigned long first_index, unsigned int max_items,
unsigned int tag);
int radix_tree_tagged(struct radix_tree_root *root, unsigned int tag);

static inline void radix_tree_preload_end(void)
Expand Down
178 changes: 155 additions & 23 deletions lib/radix-tree.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -359,18 +359,17 @@ EXPORT_SYMBOL(radix_tree_insert);
* Returns: the slot corresponding to the position @index in the
* radix tree @root. This is useful for update-if-exists operations.
*
* This function cannot be called under rcu_read_lock, it must be
* excluded from writers, as must the returned slot for subsequent
* use by radix_tree_deref_slot() and radix_tree_replace slot.
* Caller must hold tree write locked across slot lookup and
* replace.
* This function can be called under rcu_read_lock iff the slot is not
* modified by radix_tree_replace_slot, otherwise it must be called
* exclusive from other writers. Any dereference of the slot must be done
* using radix_tree_deref_slot.
*/
void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
{
unsigned int height, shift;
struct radix_tree_node *node, **slot;

node = root->rnode;
node = rcu_dereference(root->rnode);
if (node == NULL)
return NULL;

Expand All @@ -390,7 +389,7 @@ void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index)
do {
slot = (struct radix_tree_node **)
(node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK));
node = *slot;
node = rcu_dereference(*slot);
if (node == NULL)
return NULL;

Expand Down Expand Up @@ -667,7 +666,7 @@ unsigned long radix_tree_next_hole(struct radix_tree_root *root,
EXPORT_SYMBOL(radix_tree_next_hole);

static unsigned int
__lookup(struct radix_tree_node *slot, void **results, unsigned long index,
__lookup(struct radix_tree_node *slot, void ***results, unsigned long index,
unsigned int max_items, unsigned long *next_index)
{
unsigned int nr_found = 0;
Expand Down Expand Up @@ -701,11 +700,9 @@ __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++) {
struct radix_tree_node *node;
index++;
node = slot->slots[i];
if (node) {
results[nr_found++] = rcu_dereference(node);
if (slot->slots[i]) {
results[nr_found++] = &(slot->slots[i]);
if (nr_found == max_items)
goto out;
}
Expand Down Expand Up @@ -759,13 +756,22 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results,

ret = 0;
while (ret < max_items) {
unsigned int nr_found;
unsigned int nr_found, slots_found, i;
unsigned long next_index; /* Index of next search */

if (cur_index > max_index)
break;
nr_found = __lookup(node, results + ret, cur_index,
slots_found = __lookup(node, (void ***)results + ret, cur_index,
max_items - ret, &next_index);
nr_found = 0;
for (i = 0; i < slots_found; i++) {
struct radix_tree_node *slot;
slot = *(((void ***)results)[ret + i]);
if (!slot)
continue;
results[ret + nr_found] = rcu_dereference(slot);
nr_found++;
}
ret += nr_found;
if (next_index == 0)
break;
Expand All @@ -776,12 +782,71 @@ radix_tree_gang_lookup(struct radix_tree_root *root, void **results,
}
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
* @first_index: start the lookup from this key
* @max_items: place up to this many items at *results
*
* Performs an index-ascending scan of the tree for present items. Places
* their slots at *@results and returns the number of items which were
* placed at *@results.
*
* The implementation is naive.
*
* Like radix_tree_gang_lookup as far as RCU and locking goes. Slots must
* be dereferenced with radix_tree_deref_slot, and if using only RCU
* protection, radix_tree_deref_slot may fail requiring a retry.
*/
unsigned int
radix_tree_gang_lookup_slot(struct radix_tree_root *root, void ***results,
unsigned long first_index, unsigned int max_items)
{
unsigned long max_index;
struct radix_tree_node *node;
unsigned long cur_index = first_index;
unsigned int ret;

node = rcu_dereference(root->rnode);
if (!node)
return 0;

if (!radix_tree_is_indirect_ptr(node)) {
if (first_index > 0)
return 0;
results[0] = (void **)&root->rnode;
return 1;
}
node = radix_tree_indirect_to_ptr(node);

max_index = radix_tree_maxindex(node->height);

ret = 0;
while (ret < max_items) {
unsigned int slots_found;
unsigned long next_index; /* Index of next search */

if (cur_index > max_index)
break;
slots_found = __lookup(node, results + ret, cur_index,
max_items - ret, &next_index);
ret += slots_found;
if (next_index == 0)
break;
cur_index = next_index;
}

return ret;
}
EXPORT_SYMBOL(radix_tree_gang_lookup_slot);

/*
* FIXME: the two tag_get()s here should use find_next_bit() instead of
* open-coding the search.
*/
static unsigned int
__lookup_tag(struct radix_tree_node *slot, void **results, unsigned long index,
__lookup_tag(struct radix_tree_node *slot, void ***results, unsigned long index,
unsigned int max_items, unsigned long *next_index, unsigned int tag)
{
unsigned int nr_found = 0;
Expand Down Expand Up @@ -811,11 +876,9 @@ __lookup_tag(struct radix_tree_node *slot, void **results, unsigned long index,
unsigned long j = index & RADIX_TREE_MAP_MASK;

for ( ; j < RADIX_TREE_MAP_SIZE; j++) {
struct radix_tree_node *node;
index++;
if (!tag_get(slot, tag, j))
continue;
node = slot->slots[j];
/*
* Even though the tag was found set, we need to
* recheck that we have a non-NULL node, because
Expand All @@ -826,9 +889,8 @@ __lookup_tag(struct radix_tree_node *slot, void **results, unsigned long index,
* lookup ->slots[x] without a lock (ie. can't
* rely on its value remaining the same).
*/
if (node) {
node = rcu_dereference(node);
results[nr_found++] = node;
if (slot->slots[j]) {
results[nr_found++] = &(slot->slots[j]);
if (nr_found == max_items)
goto out;
}
Expand Down Expand Up @@ -887,13 +949,22 @@ radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,

ret = 0;
while (ret < max_items) {
unsigned int nr_found;
unsigned int nr_found, slots_found, i;
unsigned long next_index; /* Index of next search */

if (cur_index > max_index)
break;
nr_found = __lookup_tag(node, results + ret, cur_index,
max_items - ret, &next_index, tag);
slots_found = __lookup_tag(node, (void ***)results + ret,
cur_index, max_items - ret, &next_index, tag);
nr_found = 0;
for (i = 0; i < slots_found; i++) {
struct radix_tree_node *slot;
slot = *(((void ***)results)[ret + i]);
if (!slot)
continue;
results[ret + nr_found] = rcu_dereference(slot);
nr_found++;
}
ret += nr_found;
if (next_index == 0)
break;
Expand All @@ -904,6 +975,67 @@ radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results,
}
EXPORT_SYMBOL(radix_tree_gang_lookup_tag);

/**
* radix_tree_gang_lookup_tag_slot - perform multiple slot lookup on a
* radix tree based on a tag
* @root: radix tree root
* @results: where the results of the lookup are placed
* @first_index: start the lookup from this key
* @max_items: place up to this many items at *results
* @tag: the tag index (< RADIX_TREE_MAX_TAGS)
*
* Performs an index-ascending scan of the tree for present items which
* have the tag indexed by @tag set. Places the slots at *@results and
* returns the number of slots which were placed at *@results.
*/
unsigned int
radix_tree_gang_lookup_tag_slot(struct radix_tree_root *root, void ***results,
unsigned long first_index, unsigned int max_items,
unsigned int tag)
{
struct radix_tree_node *node;
unsigned long max_index;
unsigned long cur_index = first_index;
unsigned int ret;

/* check the root's tag bit */
if (!root_tag_get(root, tag))
return 0;

node = rcu_dereference(root->rnode);
if (!node)
return 0;

if (!radix_tree_is_indirect_ptr(node)) {
if (first_index > 0)
return 0;
results[0] = (void **)&root->rnode;
return 1;
}
node = radix_tree_indirect_to_ptr(node);

max_index = radix_tree_maxindex(node->height);

ret = 0;
while (ret < max_items) {
unsigned int slots_found;
unsigned long next_index; /* Index of next search */

if (cur_index > max_index)
break;
slots_found = __lookup_tag(node, results + ret,
cur_index, max_items - ret, &next_index, tag);
ret += slots_found;
if (next_index == 0)
break;
cur_index = next_index;
}

return ret;
}
EXPORT_SYMBOL(radix_tree_gang_lookup_tag_slot);


/**
* radix_tree_shrink - shrink height of a radix tree to minimal
* @root radix tree root
Expand Down

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