lib: radix-tree: add entry deletion support to __radix_tree_replace()
Page cache shadow entry handling will be a lot simpler when it can use a single generic replacement function for pages, shadow entries, and emptying slots. Make __radix_tree_replace() properly account insertions and deletions in node->count and garbage collect nodes as they become empty. Then re-implement radix_tree_delete() on top of it. Link: http://lkml.kernel.org/r/20161117193058.GC23430@cmpxchg.org Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: Matthew Wilcox <mawilcox@linuxonhyperv.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Johannes Weiner
Linus Torvalds
parent
6d75f366b9
commit
f4b109c6da
227
lib/radix-tree.c
227
lib/radix-tree.c
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@ -538,6 +538,107 @@ static int radix_tree_extend(struct radix_tree_root *root,
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return maxshift + RADIX_TREE_MAP_SHIFT;
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}
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/**
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* radix_tree_shrink - shrink radix tree to minimum height
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* @root radix tree root
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*/
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static inline bool radix_tree_shrink(struct radix_tree_root *root)
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{
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bool shrunk = false;
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for (;;) {
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struct radix_tree_node *node = root->rnode;
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struct radix_tree_node *child;
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if (!radix_tree_is_internal_node(node))
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break;
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node = entry_to_node(node);
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/*
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* The candidate node has more than one child, or its child
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* is not at the leftmost slot, or the child is a multiorder
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* entry, we cannot shrink.
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*/
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if (node->count != 1)
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break;
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child = node->slots[0];
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if (!child)
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break;
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if (!radix_tree_is_internal_node(child) && node->shift)
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break;
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if (radix_tree_is_internal_node(child))
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entry_to_node(child)->parent = NULL;
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/*
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* We don't need rcu_assign_pointer(), since we are simply
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* moving the node from one part of the tree to another: if it
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* was safe to dereference the old pointer to it
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* (node->slots[0]), it will be safe to dereference the new
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* one (root->rnode) as far as dependent read barriers go.
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*/
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root->rnode = child;
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/*
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* We have a dilemma here. The node's slot[0] must not be
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* NULLed in case there are concurrent lookups expecting to
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* find the item. However if this was a bottom-level node,
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* then it may be subject to the slot pointer being visible
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* to callers dereferencing it. If item corresponding to
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* slot[0] is subsequently deleted, these callers would expect
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* their slot to become empty sooner or later.
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*
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* For example, lockless pagecache will look up a slot, deref
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* the page pointer, and if the page has 0 refcount it means it
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* was concurrently deleted from pagecache so try the deref
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* again. Fortunately there is already a requirement for logic
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* to retry the entire slot lookup -- the indirect pointer
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* problem (replacing direct root node with an indirect pointer
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* also results in a stale slot). So tag the slot as indirect
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* to force callers to retry.
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*/
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if (!radix_tree_is_internal_node(child))
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node->slots[0] = RADIX_TREE_RETRY;
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radix_tree_node_free(node);
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shrunk = true;
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}
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return shrunk;
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}
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static bool delete_node(struct radix_tree_root *root,
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struct radix_tree_node *node)
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{
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bool deleted = false;
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do {
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struct radix_tree_node *parent;
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if (node->count) {
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if (node == entry_to_node(root->rnode))
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deleted |= radix_tree_shrink(root);
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return deleted;
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}
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parent = node->parent;
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if (parent) {
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parent->slots[node->offset] = NULL;
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parent->count--;
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} else {
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root_tag_clear_all(root);
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root->rnode = NULL;
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}
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radix_tree_node_free(node);
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deleted = true;
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node = parent;
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} while (node);
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return deleted;
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}
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/**
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* __radix_tree_create - create a slot in a radix tree
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* @root: radix tree root
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@ -759,18 +860,20 @@ static void replace_slot(struct radix_tree_root *root,
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bool warn_typeswitch)
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{
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void *old = rcu_dereference_raw(*slot);
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int exceptional;
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int count, exceptional;
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WARN_ON_ONCE(radix_tree_is_internal_node(item));
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WARN_ON_ONCE(!!item - !!old);
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count = !!item - !!old;
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exceptional = !!radix_tree_exceptional_entry(item) -
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!!radix_tree_exceptional_entry(old);
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WARN_ON_ONCE(warn_typeswitch && exceptional);
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WARN_ON_ONCE(warn_typeswitch && (count || exceptional));
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if (node)
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if (node) {
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node->count += count;
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node->exceptional += exceptional;
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}
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rcu_assign_pointer(*slot, item);
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}
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@ -790,12 +893,14 @@ void __radix_tree_replace(struct radix_tree_root *root,
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void **slot, void *item)
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{
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/*
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* This function supports replacing exceptional entries, but
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* that needs accounting against the node unless the slot is
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* root->rnode.
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* This function supports replacing exceptional entries and
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* deleting entries, but that needs accounting against the
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* node unless the slot is root->rnode.
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*/
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replace_slot(root, node, slot, item,
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!node && slot != (void **)&root->rnode);
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delete_node(root, node);
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}
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/**
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@ -810,8 +915,8 @@ void __radix_tree_replace(struct radix_tree_root *root,
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*
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* NOTE: This cannot be used to switch between non-entries (empty slots),
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* regular entries, and exceptional entries, as that requires accounting
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* inside the radix tree node. When switching from one type of entry to
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* another, use __radix_tree_lookup() and __radix_tree_replace().
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* inside the radix tree node. When switching from one type of entry or
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* deleting, use __radix_tree_lookup() and __radix_tree_replace().
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*/
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void radix_tree_replace_slot(struct radix_tree_root *root,
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void **slot, void *item)
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@ -1466,75 +1571,6 @@ unsigned long radix_tree_locate_item(struct radix_tree_root *root, void *item)
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}
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#endif /* CONFIG_SHMEM && CONFIG_SWAP */
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/**
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* radix_tree_shrink - shrink radix tree to minimum height
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* @root radix tree root
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*/
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static inline bool radix_tree_shrink(struct radix_tree_root *root)
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{
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bool shrunk = false;
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for (;;) {
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struct radix_tree_node *node = root->rnode;
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struct radix_tree_node *child;
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if (!radix_tree_is_internal_node(node))
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break;
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node = entry_to_node(node);
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/*
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* The candidate node has more than one child, or its child
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* is not at the leftmost slot, or the child is a multiorder
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* entry, we cannot shrink.
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*/
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if (node->count != 1)
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break;
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child = node->slots[0];
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if (!child)
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break;
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if (!radix_tree_is_internal_node(child) && node->shift)
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break;
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if (radix_tree_is_internal_node(child))
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entry_to_node(child)->parent = NULL;
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/*
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* We don't need rcu_assign_pointer(), since we are simply
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* moving the node from one part of the tree to another: if it
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* was safe to dereference the old pointer to it
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* (node->slots[0]), it will be safe to dereference the new
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* one (root->rnode) as far as dependent read barriers go.
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*/
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root->rnode = child;
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/*
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* We have a dilemma here. The node's slot[0] must not be
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* NULLed in case there are concurrent lookups expecting to
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* find the item. However if this was a bottom-level node,
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* then it may be subject to the slot pointer being visible
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* to callers dereferencing it. If item corresponding to
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* slot[0] is subsequently deleted, these callers would expect
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* their slot to become empty sooner or later.
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*
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* For example, lockless pagecache will look up a slot, deref
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* the page pointer, and if the page has 0 refcount it means it
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* was concurrently deleted from pagecache so try the deref
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* again. Fortunately there is already a requirement for logic
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* to retry the entire slot lookup -- the indirect pointer
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* problem (replacing direct root node with an indirect pointer
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* also results in a stale slot). So tag the slot as indirect
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* to force callers to retry.
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*/
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if (!radix_tree_is_internal_node(child))
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node->slots[0] = RADIX_TREE_RETRY;
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radix_tree_node_free(node);
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shrunk = true;
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}
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return shrunk;
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}
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/**
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* __radix_tree_delete_node - try to free node after clearing a slot
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* @root: radix tree root
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@ -1549,33 +1585,7 @@ static inline bool radix_tree_shrink(struct radix_tree_root *root)
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bool __radix_tree_delete_node(struct radix_tree_root *root,
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struct radix_tree_node *node)
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{
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bool deleted = false;
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do {
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struct radix_tree_node *parent;
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if (node->count) {
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if (node == entry_to_node(root->rnode))
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deleted |= radix_tree_shrink(root);
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return deleted;
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}
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parent = node->parent;
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if (parent) {
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parent->slots[node->offset] = NULL;
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parent->count--;
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} else {
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root_tag_clear_all(root);
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root->rnode = NULL;
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}
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radix_tree_node_free(node);
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deleted = true;
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node = parent;
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} while (node);
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return deleted;
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return delete_node(root, node);
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}
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static inline void delete_sibling_entries(struct radix_tree_node *node,
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@ -1632,12 +1642,7 @@ void *radix_tree_delete_item(struct radix_tree_root *root,
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node_tag_clear(root, node, tag, offset);
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delete_sibling_entries(node, node_to_entry(slot), offset);
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node->slots[offset] = NULL;
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node->count--;
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if (radix_tree_exceptional_entry(entry))
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node->exceptional--;
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__radix_tree_delete_node(root, node);
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__radix_tree_replace(root, node, slot, NULL);
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return entry;
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}
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