diff options
| -rw-r--r-- | include/linux/radix-tree.h | 101 | ||||
| -rw-r--r-- | lib/radix-tree.c | 327 | ||||
| -rw-r--r-- | mm/migrate.c | 19 |
3 files changed, 340 insertions, 107 deletions
diff --git a/include/linux/radix-tree.h b/include/linux/radix-tree.h index cbfa115..0deb842 100644 --- a/include/linux/radix-tree.h +++ b/include/linux/radix-tree.h @@ -1,6 +1,7 @@ /* * Copyright (C) 2001 Momchil Velikov * Portions Copyright (C) 2001 Christoph Hellwig + * Copyright (C) 2006 Nick Piggin * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License as @@ -21,6 +22,35 @@ #include <linux/preempt.h> #include <linux/types.h> +#include <linux/kernel.h> +#include <linux/rcupdate.h> + +/* + * A direct pointer (root->rnode pointing directly to a data item, + * rather than another radix_tree_node) is signalled by the low bit + * set in the root->rnode pointer. + * + * In this case root->height is also NULL, but the direct pointer tests are + * needed for RCU lookups when root->height is unreliable. + */ +#define RADIX_TREE_DIRECT_PTR 1 + +static inline void *radix_tree_ptr_to_direct(void *ptr) +{ + return (void *)((unsigned long)ptr | RADIX_TREE_DIRECT_PTR); +} + +static inline void *radix_tree_direct_to_ptr(void *ptr) +{ + return (void *)((unsigned long)ptr & ~RADIX_TREE_DIRECT_PTR); +} + +static inline int radix_tree_is_direct_ptr(void *ptr) +{ + return (int)((unsigned long)ptr & RADIX_TREE_DIRECT_PTR); +} + +/*** radix-tree API starts here ***/ #define RADIX_TREE_MAX_TAGS 2 @@ -47,6 +77,77 @@ do { \ (root)->rnode = NULL; \ } while (0) +/** + * Radix-tree synchronization + * + * The radix-tree API requires that users provide all synchronisation (with + * specific exceptions, noted below). + * + * Synchronization of access to the data items being stored in the tree, and + * management of their lifetimes must be completely managed by API users. + * + * For API usage, in general, + * - any function _modifying_ the the tree or tags (inserting or deleting + * items, setting or clearing tags must exclude other modifications, and + * exclude any functions reading the tree. + * - any function _reading_ the the tree or tags (looking up items or tags, + * gang lookups) must exclude modifications to the tree, but may occur + * concurrently with other readers. + * + * The notable exceptions to this rule are the following functions: + * radix_tree_lookup + * radix_tree_tag_get + * radix_tree_gang_lookup + * radix_tree_gang_lookup_tag + * radix_tree_tagged + * + * The first 4 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. + * + * It is still required that the caller manage the synchronization and lifetimes + * of the items. So if RCU lock-free lookups are used, typically this would mean + * that the items have their own locks, or are amenable to lock-free access; and + * that the items are freed by RCU (or only freed after having been deleted from + * the radix tree *and* a synchronize_rcu() grace period). + * + * (Note, rcu_assign_pointer and rcu_dereference are not needed to control + * access to data items when inserting into or looking up from the radix tree) + * + * radix_tree_tagged is able to be called without locking or RCU. + */ + +/** + * radix_tree_deref_slot - dereference a slot + * @pslot: pointer to slot, returned by radix_tree_lookup_slot + * Returns: item that was stored in that slot with any direct pointer flag + * removed. + * + * For use with radix_tree_lookup_slot(). Caller must hold tree at least read + * locked across slot lookup and dereference. More likely, will be used with + * radix_tree_replace_slot(), as well, so caller will hold tree write locked. + */ +static inline void *radix_tree_deref_slot(void **pslot) +{ + return radix_tree_direct_to_ptr(*pslot); +} +/** + * radix_tree_replace_slot - replace item in a slot + * @pslot: pointer to slot, returned by radix_tree_lookup_slot + * @item: new item to store in the slot. + * + * For use with radix_tree_lookup_slot(). Caller must hold tree write locked + * across slot lookup and replacement. + */ +static inline void radix_tree_replace_slot(void **pslot, void *item) +{ + BUG_ON(radix_tree_is_direct_ptr(item)); + rcu_assign_pointer(*pslot, + (void *)((unsigned long)item | + ((unsigned long)*pslot & RADIX_TREE_DIRECT_PTR))); +} + int radix_tree_insert(struct radix_tree_root *, unsigned long, void *); void *radix_tree_lookup(struct radix_tree_root *, unsigned long); void **radix_tree_lookup_slot(struct radix_tree_root *, unsigned long); diff --git a/lib/radix-tree.c b/lib/radix-tree.c index 9eb2595..e2cefab 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -2,6 +2,7 @@ * Copyright (C) 2001 Momchil Velikov * Portions Copyright (C) 2001 Christoph Hellwig * Copyright (C) 2005 SGI, Christoph Lameter <clameter@sgi.com> + * Copyright (C) 2006 Nick Piggin * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License as @@ -30,6 +31,7 @@ #include <linux/gfp.h> #include <linux/string.h> #include <linux/bitops.h> +#include <linux/rcupdate.h> #ifdef __KERNEL__ @@ -45,7 +47,9 @@ ((RADIX_TREE_MAP_SIZE + BITS_PER_LONG - 1) / BITS_PER_LONG) struct radix_tree_node { + unsigned int height; /* Height from the bottom */ unsigned int count; + struct rcu_head rcu_head; void *slots[RADIX_TREE_MAP_SIZE]; unsigned long tags[RADIX_TREE_MAX_TAGS][RADIX_TREE_TAG_LONGS]; }; @@ -100,13 +104,21 @@ radix_tree_node_alloc(struct radix_tree_root *root) rtp->nr--; } } + BUG_ON(radix_tree_is_direct_ptr(ret)); return ret; } +static void radix_tree_node_rcu_free(struct rcu_head *head) +{ + struct radix_tree_node *node = + container_of(head, struct radix_tree_node, rcu_head); + kmem_cache_free(radix_tree_node_cachep, node); +} + static inline void radix_tree_node_free(struct radix_tree_node *node) { - kmem_cache_free(radix_tree_node_cachep, node); + call_rcu(&node->rcu_head, radix_tree_node_rcu_free); } /* @@ -222,11 +234,12 @@ static int radix_tree_extend(struct radix_tree_root *root, unsigned long index) } do { + unsigned int newheight; if (!(node = radix_tree_node_alloc(root))) return -ENOMEM; /* Increase the height. */ - node->slots[0] = root->rnode; + node->slots[0] = radix_tree_direct_to_ptr(root->rnode); /* Propagate the aggregated tag info into the new root */ for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) { @@ -234,9 +247,11 @@ static int radix_tree_extend(struct radix_tree_root *root, unsigned long index) tag_set(node, tag, 0); } + newheight = root->height+1; + node->height = newheight; node->count = 1; - root->rnode = node; - root->height++; + rcu_assign_pointer(root->rnode, node); + root->height = newheight; } while (height > root->height); out: return 0; @@ -258,6 +273,8 @@ int radix_tree_insert(struct radix_tree_root *root, int offset; int error; + BUG_ON(radix_tree_is_direct_ptr(item)); + /* Make sure the tree is high enough. */ if (index > radix_tree_maxindex(root->height)) { error = radix_tree_extend(root, index); @@ -275,11 +292,12 @@ int radix_tree_insert(struct radix_tree_root *root, /* Have to add a child node. */ if (!(slot = radix_tree_node_alloc(root))) return -ENOMEM; + slot->height = height; if (node) { - node->slots[offset] = slot; + rcu_assign_pointer(node->slots[offset], slot); node->count++; } else - root->rnode = slot; + rcu_assign_pointer(root->rnode, slot); } /* Go a level down */ @@ -295,11 +313,11 @@ int radix_tree_insert(struct radix_tree_root *root, if (node) { node->count++; - node->slots[offset] = item; + rcu_assign_pointer(node->slots[offset], item); BUG_ON(tag_get(node, 0, offset)); BUG_ON(tag_get(node, 1, offset)); } else { - root->rnode = item; + rcu_assign_pointer(root->rnode, radix_tree_ptr_to_direct(item)); BUG_ON(root_tag_get(root, 0)); BUG_ON(root_tag_get(root, 1)); } @@ -308,49 +326,54 @@ int radix_tree_insert(struct radix_tree_root *root, } EXPORT_SYMBOL(radix_tree_insert); -static inline void **__lookup_slot(struct radix_tree_root *root, - unsigned long index) +/** + * radix_tree_lookup_slot - lookup a slot in a radix tree + * @root: radix tree root + * @index: index key + * + * 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. + */ +void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index) { unsigned int height, shift; - struct radix_tree_node **slot; - - height = root->height; + struct radix_tree_node *node, **slot; - if (index > radix_tree_maxindex(height)) + node = root->rnode; + if (node == NULL) return NULL; - if (height == 0 && root->rnode) + if (radix_tree_is_direct_ptr(node)) { + if (index > 0) + return NULL; return (void **)&root->rnode; + } + + height = node->height; + if (index > radix_tree_maxindex(height)) + return NULL; shift = (height-1) * RADIX_TREE_MAP_SHIFT; - slot = &root->rnode; - while (height > 0) { - if (*slot == NULL) + do { + slot = (struct radix_tree_node **) + (node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK)); + node = *slot; + if (node == NULL) return NULL; - slot = (struct radix_tree_node **) - ((*slot)->slots + - ((index >> shift) & RADIX_TREE_MAP_MASK)); shift -= RADIX_TREE_MAP_SHIFT; height--; - } + } while (height > 0); return (void **)slot; } - -/** - * radix_tree_lookup_slot - lookup a slot in a radix tree - * @root: radix tree root - * @index: index key - * - * Lookup the slot corresponding to the position @index in the radix tree - * @root. This is useful for update-if-exists operations. - */ -void **radix_tree_lookup_slot(struct radix_tree_root *root, unsigned long index) -{ - return __lookup_slot(root, index); -} EXPORT_SYMBOL(radix_tree_lookup_slot); /** @@ -359,13 +382,45 @@ EXPORT_SYMBOL(radix_tree_lookup_slot); * @index: index key * * Lookup the item at the position @index in the radix tree @root. + * + * This function can be called under rcu_read_lock, however the caller + * must manage lifetimes of leaf nodes (eg. RCU may also be used to free + * them safely). No RCU barriers are required to access or modify the + * returned item, however. */ void *radix_tree_lookup(struct radix_tree_root *root, unsigned long index) { - void **slot; + unsigned int height, shift; + struct radix_tree_node *node, **slot; + + node = rcu_dereference(root->rnode); + if (node == NULL) + return NULL; + + if (radix_tree_is_direct_ptr(node)) { + if (index > 0) + return NULL; + return radix_tree_direct_to_ptr(node); + } + + height = node->height; + if (index > radix_tree_maxindex(height)) + return NULL; + + shift = (height-1) * RADIX_TREE_MAP_SHIFT; - slot = __lookup_slot(root, index); - return slot != NULL ? *slot : NULL; + do { + slot = (struct radix_tree_node **) + (node->slots + ((index>>shift) & RADIX_TREE_MAP_MASK)); + node = rcu_dereference(*slot); + if (node == NULL) + return NULL; + + shift -= RADIX_TREE_MAP_SHIFT; + height--; + } while (height > 0); + + return node; } EXPORT_SYMBOL(radix_tree_lookup); @@ -495,27 +550,30 @@ int radix_tree_tag_get(struct radix_tree_root *root, unsigned long index, unsigned int tag) { unsigned int height, shift; - struct radix_tree_node *slot; + struct radix_tree_node *node; int saw_unset_tag = 0; - height = root->height; - if (index > radix_tree_maxindex(height)) - return 0; - /* check the root's tag bit */ if (!root_tag_get(root, tag)) return 0; - if (height == 0) - return 1; + node = rcu_dereference(root->rnode); + if (node == NULL) + return 0; + + if (radix_tree_is_direct_ptr(node)) + return (index == 0); + + height = node->height; + if (index > radix_tree_maxindex(height)) + return 0; shift = (height - 1) * RADIX_TREE_MAP_SHIFT; - slot = root->rnode; for ( ; ; ) { int offset; - if (slot == NULL) + if (node == NULL) return 0; offset = (index >> shift) & RADIX_TREE_MAP_MASK; @@ -524,15 +582,15 @@ int radix_tree_tag_get(struct radix_tree_root *root, * This is just a debug check. Later, we can bale as soon as * we see an unset tag. */ - if (!tag_get(slot, tag, offset)) + if (!tag_get(node, tag, offset)) saw_unset_tag = 1; if (height == 1) { - int ret = tag_get(slot, tag, offset); + int ret = tag_get(node, tag, offset); BUG_ON(ret && saw_unset_tag); return !!ret; } - slot = slot->slots[offset]; + node = rcu_dereference(node->slots[offset]); shift -= RADIX_TREE_MAP_SHIFT; height--; } @@ -541,47 +599,45 @@ EXPORT_SYMBOL(radix_tree_tag_get); #endif static unsigned int -__lookup(struct radix_tree_root *root, 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; unsigned int shift, height; - struct radix_tree_node *slot; unsigned long i; - height = root->height; - if (height == 0) { - if (root->rnode && index == 0) - results[nr_found++] = root->rnode; + height = slot->height; + if (height == 0) goto out; - } - shift = (height-1) * RADIX_TREE_MAP_SHIFT; - slot = root->rnode; for ( ; height > 1; height--) { - - for (i = (index >> shift) & RADIX_TREE_MAP_MASK ; - i < RADIX_TREE_MAP_SIZE; i++) { + i = (index >> shift) & RADIX_TREE_MAP_MASK; + for (;;) { if (slot->slots[i] != NULL) break; index &= ~((1UL << shift) - 1); index += 1UL << shift; if (index == 0) goto out; /* 32-bit wraparound */ + i++; + if (i == RADIX_TREE_MAP_SIZE) + goto out; } - if (i == RADIX_TREE_MAP_SIZE) - goto out; shift -= RADIX_TREE_MAP_SHIFT; - slot = slot->slots[i]; + slot = rcu_dereference(slot->slots[i]); + if (slot == NULL) + goto out; } /* Bottom level: grab some items */ for (i = index & RADIX_TREE_MAP_MASK; i < RADIX_TREE_MAP_SIZE; i++) { + struct radix_tree_node *node; index++; - if (slot->slots[i]) { - results[nr_found++] = slot->slots[i]; + node = slot->slots[i]; + if (node) { + results[nr_found++] = rcu_dereference(node); if (nr_found == max_items) goto out; } @@ -603,28 +659,51 @@ out: * *@results. * * The implementation is naive. + * + * Like radix_tree_lookup, radix_tree_gang_lookup may be called under + * rcu_read_lock. In this case, rather than the returned results being + * an atomic snapshot of the tree at a single point in time, the semantics + * of an RCU protected gang lookup are as though multiple radix_tree_lookups + * have been issued in individual locks, and results stored in 'results'. */ unsigned int radix_tree_gang_lookup(struct radix_tree_root *root, void **results, unsigned long first_index, unsigned int max_items) { - const unsigned long max_index = radix_tree_maxindex(root->height); + unsigned long max_index; + struct radix_tree_node *node; unsigned long cur_index = first_index; - unsigned int ret = 0; + unsigned int ret; + + node = rcu_dereference(root->rnode); + if (!node) + return 0; + if (radix_tree_is_direct_ptr(node)) { + if (first_index > 0) + return 0; + node = radix_tree_direct_to_ptr(node); + results[0] = rcu_dereference(node); + return 1; + } + + max_index = radix_tree_maxindex(node->height); + + ret = 0; while (ret < max_items) { unsigned int nr_found; unsigned long next_index; /* Index of next search */ if (cur_index > max_index) break; - nr_found = __lookup(root, results + ret, cur_index, + nr_found = __lookup(node, results + ret, cur_index, max_items - ret, &next_index); ret += nr_found; if (next_index == 0) break; cur_index = next_index; } + return ret; } EXPORT_SYMBOL(radix_tree_gang_lookup); @@ -634,55 +713,64 @@ EXPORT_SYMBOL(radix_tree_gang_lookup); * open-coding the search. */ static unsigned int -__lookup_tag(struct radix_tree_root *root, 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; - unsigned int shift; - unsigned int height = root->height; - struct radix_tree_node *slot; + unsigned int shift, height; - if (height == 0) { - if (root->rnode && index == 0) - results[nr_found++] = root->rnode; + height = slot->height; + if (height == 0) goto out; - } - - shift = (height - 1) * RADIX_TREE_MAP_SHIFT; - slot = root->rnode; + shift = (height-1) * RADIX_TREE_MAP_SHIFT; - do { - unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK; + while (height > 0) { + unsigned long i = (index >> shift) & RADIX_TREE_MAP_MASK ; - for ( ; i < RADIX_TREE_MAP_SIZE; i++) { - if (tag_get(slot, tag, i)) { - BUG_ON(slot->slots[i] == NULL); + for (;;) { + if (tag_get(slot, tag, i)) break; - } index &= ~((1UL << shift) - 1); index += 1UL << shift; if (index == 0) goto out; /* 32-bit wraparound */ + i++; + if (i == RADIX_TREE_MAP_SIZE) + goto out; } - if (i == RADIX_TREE_MAP_SIZE) - goto out; height--; if (height == 0) { /* Bottom level: grab some items */ 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)) { - BUG_ON(slot->slots[j] == NULL); - results[nr_found++] = slot->slots[j]; + 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 + * if this lookup is lockless, it may have been + * subsequently deleted. + * + * Similar care must be taken in any place that + * 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 (nr_found == max_items) goto out; } } } shift -= RADIX_TREE_MAP_SHIFT; - slot = slot->slots[i]; - } while (height > 0); + slot = rcu_dereference(slot->slots[i]); + if (slot == NULL) + break; + } out: *next_index = index; return nr_found; @@ -706,27 +794,44 @@ radix_tree_gang_lookup_tag(struct radix_tree_root *root, void **results, unsigned long first_index, unsigned int max_items, unsigned int tag) { - const unsigned long max_index = radix_tree_maxindex(root->height); + struct radix_tree_node *node; + unsigned long max_index; unsigned long cur_index = first_index; - unsigned int ret = 0; + 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_direct_ptr(node)) { + if (first_index > 0) + return 0; + node = radix_tree_direct_to_ptr(node); + results[0] = rcu_dereference(node); + return 1; + } + + max_index = radix_tree_maxindex(node->height); + + ret = 0; while (ret < max_items) { unsigned int nr_found; unsigned long next_index; /* Index of next search */ if (cur_index > max_index) break; - nr_found = __lookup_tag(root, results + ret, cur_index, + nr_found = __lookup_tag(node, results + ret, cur_index, max_items - ret, &next_index, tag); ret += nr_found; if (next_index == 0) break; cur_index = next_index; } + return ret; } EXPORT_SYMBOL(radix_tree_gang_lookup_tag); @@ -742,8 +847,19 @@ static inline void radix_tree_shrink(struct radix_tree_root *root) root->rnode->count == 1 && root->rnode->slots[0]) { struct radix_tree_node *to_free = root->rnode; + void *newptr; - root->rnode = to_free->slots[0]; + /* + * We don't need rcu_assign_pointer(), since we are simply + * moving the node from one part of the tree to another. If + * it was safe to dereference the old pointer to it + * (to_free->slots[0]), it will be safe to dereference the new + * one (root->rnode). + */ + newptr = to_free->slots[0]; + if (root->height == 1) + newptr = radix_tree_ptr_to_direct(newptr); + root->rnode = newptr; root->height--; /* must only free zeroed nodes into the slab */ tag_clear(to_free, 0, 0); @@ -767,6 +883,7 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index) { struct radix_tree_path path[RADIX_TREE_MAX_PATH], *pathp = path; struct radix_tree_node *slot = NULL; + struct radix_tree_node *to_free; unsigned int height, shift; int tag; int offset; @@ -777,6 +894,7 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index) slot = root->rnode; if (height == 0 && root->rnode) { + slot = radix_tree_direct_to_ptr(slot); root_tag_clear_all(root); root->rnode = NULL; goto out; @@ -809,10 +927,17 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index) radix_tree_tag_clear(root, index, tag); } + to_free = NULL; /* Now free the nodes we do not need anymore */ while (pathp->node) { pathp->node->slots[pathp->offset] = NULL; pathp->node->count--; + /* + * Queue the node for deferred freeing after the + * last reference to it disappears (set NULL, above). + */ + if (to_free) + radix_tree_node_free(to_free); if (pathp->node->count) { if (pathp->node == root->rnode) @@ -821,13 +946,15 @@ void *radix_tree_delete(struct radix_tree_root *root, unsigned long index) } /* Node with zero slots in use so free it */ - radix_tree_node_free(pathp->node); - + to_free = pathp->node; pathp--; + } root_tag_clear_all(root); root->height = 0; root->rnode = NULL; + if (to_free) + radix_tree_node_free(to_free); out: return slot; diff --git a/mm/migrate.c b/mm/migrate.c index b4979d4..e9b161b 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -294,7 +294,7 @@ out: static int migrate_page_move_mapping(struct address_space *mapping, struct page *newpage, struct page *page) { - struct page **radix_pointer; + void **pslot; if (!mapping) { /* Anonymous page */ @@ -305,12 +305,11 @@ static int migrate_page_move_mapping(struct address_space *mapping, write_lock_irq(&mapping->tree_lock); - radix_pointer = (struct page **)radix_tree_lookup_slot( - &mapping->page_tree, - page_index(page)); + pslot = radix_tree_lookup_slot(&mapping->page_tree, + page_index(page)); if (page_count(page) != 2 + !!PagePrivate(page) || - *radix_pointer != page) { + (struct page *)radix_tree_deref_slot(pslot) != page) { write_unlock_irq(&mapping->tree_lock); return -EAGAIN; } @@ -318,7 +317,7 @@ static int migrate_page_move_mapping(struct address_space *mapping, /* * Now we know that no one else is looking at the page. */ - get_page(newpage); + get_page(newpage); /* add cache reference */ #ifdef CONFIG_SWAP if (PageSwapCache(page)) { SetPageSwapCache(newpage); @@ -326,8 +325,14 @@ static int migrate_page_move_mapping(struct address_space *mapping, } #endif - *radix_pointer = newpage; + radix_tree_replace_slot(pslot, newpage); + + /* + * Drop cache reference from old page. + * We know this isn't the last reference. + */ __put_page(page); + write_unlock_irq(&mapping->tree_lock); return 0; |
