From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754394AbdLFBB4 (ORCPT ); Tue, 5 Dec 2017 20:01:56 -0500 Received: from bombadil.infradead.org ([65.50.211.133]:60183 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753311AbdLFAmK (ORCPT ); Tue, 5 Dec 2017 19:42:10 -0500 From: Matthew Wilcox Cc: Matthew Wilcox , Ross Zwisler , Jens Axboe , Rehas Sachdeva , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-nilfs@vger.kernel.org, linux-btrfs@vger.kernel.org, linux-xfs@vger.kernel.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 05/73] xarray: Change definition of sibling entries Date: Tue, 5 Dec 2017 16:40:51 -0800 Message-Id: <20171206004159.3755-6-willy@infradead.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20171206004159.3755-1-willy@infradead.org> References: <20171206004159.3755-1-willy@infradead.org> To: unlisted-recipients:; (no To-header on input) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Matthew Wilcox Instead of storing a pointer to the slot containing the canonical entry, store the offset of the slot. Produces slightly more efficient code (~300 bytes) and simplifies the implementation. Signed-off-by: Matthew Wilcox --- include/linux/xarray.h | 82 ++++++++++++++++++++++++++++++++++++++++++++++++++ lib/radix-tree.c | 65 +++++++++++---------------------------- 2 files changed, 100 insertions(+), 47 deletions(-) diff --git a/include/linux/xarray.h b/include/linux/xarray.h index e55f5cfd14ed..2c45d87a3476 100644 --- a/include/linux/xarray.h +++ b/include/linux/xarray.h @@ -58,6 +58,8 @@ static inline bool xa_is_value(void *entry) return (unsigned long)entry & 1; } +/* Everything below here is the Advanced API. Proceed with caution. */ + #define xa_trylock(xa) spin_trylock(&(xa)->xa_lock) #define xa_lock(xa) spin_lock(&(xa)->xa_lock) #define xa_unlock(xa) spin_unlock(&(xa)->xa_lock) @@ -71,4 +73,84 @@ static inline bool xa_is_value(void *entry) spin_unlock_irqrestore(&(xa)->xa_lock, flags) #define xa_lock_held(xa) lockdep_is_held(&(xa)->xa_lock) +/* + * The xarray is constructed out of a set of 'chunks' of pointers. Choosing + * the best chunk size requires some tradeoffs. A power of two recommends + * itself so that we can walk the tree based purely on shifts and masks. + * Generally, the larger the better; as the number of slots per level of the + * tree increases, the less tall the tree needs to be. But that needs to be + * balanced against the memory consumption of each node. On a 64-bit system, + * xa_node is currently 576 bytes, and we get 7 of them per 4kB page. If we + * doubled the number of slots per node, we'd get only 3 nodes per 4kB page. + */ +#ifndef XA_CHUNK_SHIFT +#define XA_CHUNK_SHIFT (CONFIG_BASE_SMALL ? 4 : 6) +#endif +#define XA_CHUNK_SIZE (1UL << XA_CHUNK_SHIFT) +#define XA_CHUNK_MASK (XA_CHUNK_SIZE - 1) + +/* + * Internal entries have the bottom two bits set to the value 10b. Most + * internal entries are pointers to the next node in the tree. Since the + * kernel unmaps page 0 to trap NULL pointer dereferences, we can use values + * 0-1023 for special purposes. Values 0-62 are used for sibling + * entries. Value 256 is used for the retry entry. + */ + +/* Private */ +static inline void *xa_mk_internal(unsigned long v) +{ + return (void *)((v << 2) | 2); +} + +/* Private */ +static inline unsigned long xa_to_internal(void *entry) +{ + return (unsigned long)entry >> 2; +} + +/** + * xa_is_internal() - Is the entry an internal entry? + * @entry: Entry retrieved from the XArray + * + * Return: %true if the entry is an internal entry. + */ +static inline bool xa_is_internal(void *entry) +{ + return ((unsigned long)entry & 3) == 2; +} + +/* Private */ +static inline bool xa_is_node(void *entry) +{ + return xa_is_internal(entry) && (unsigned long)entry > 4096; +} + +/* Private */ +static inline void *xa_mk_sibling(unsigned int offset) +{ + return xa_mk_internal(offset); +} + +/* Private */ +static inline unsigned long xa_to_sibling(void *entry) +{ + return xa_to_internal(entry); +} + +/** + * xa_is_sibling() - Is the entry a sibling entry? + * @entry: Entry retrieved from the XArray + * + * Return: %true if the entry is a sibling entry. + */ +static inline bool xa_is_sibling(void *entry) +{ + return IS_ENABLED(CONFIG_RADIX_TREE_MULTIORDER) && + xa_is_internal(entry) && + (entry < xa_mk_sibling(XA_CHUNK_SIZE - 1)); +} + +#define XA_RETRY_ENTRY xa_mk_internal(256) + #endif /* _LINUX_XARRAY_H */ diff --git a/lib/radix-tree.c b/lib/radix-tree.c index cda7a730e591..0a7a21dd9398 100644 --- a/lib/radix-tree.c +++ b/lib/radix-tree.c @@ -37,6 +37,7 @@ #include #include #include +#include /* Number of nodes in fully populated tree of given height */ @@ -97,24 +98,7 @@ static inline void *node_to_entry(void *ptr) return (void *)((unsigned long)ptr | RADIX_TREE_INTERNAL_NODE); } -#define RADIX_TREE_RETRY node_to_entry(NULL) - -#ifdef CONFIG_RADIX_TREE_MULTIORDER -/* Sibling slots point directly to another slot in the same node */ -static inline -bool is_sibling_entry(const struct radix_tree_node *parent, void *node) -{ - void __rcu **ptr = node; - return (parent->slots <= ptr) && - (ptr < parent->slots + RADIX_TREE_MAP_SIZE); -} -#else -static inline -bool is_sibling_entry(const struct radix_tree_node *parent, void *node) -{ - return false; -} -#endif +#define RADIX_TREE_RETRY XA_RETRY_ENTRY static inline unsigned long get_slot_offset(const struct radix_tree_node *parent, void __rcu **slot) @@ -128,16 +112,10 @@ static unsigned int radix_tree_descend(const struct radix_tree_node *parent, unsigned int offset = (index >> parent->shift) & RADIX_TREE_MAP_MASK; void __rcu **entry = rcu_dereference_raw(parent->slots[offset]); -#ifdef CONFIG_RADIX_TREE_MULTIORDER - if (radix_tree_is_internal_node(entry)) { - if (is_sibling_entry(parent, entry)) { - void __rcu **sibentry; - sibentry = (void __rcu **) entry_to_node(entry); - offset = get_slot_offset(parent, sibentry); - entry = rcu_dereference_raw(*sibentry); - } + if (xa_is_sibling(entry)) { + offset = xa_to_sibling(entry); + entry = rcu_dereference_raw(parent->slots[offset]); } -#endif *nodep = (void *)entry; return offset; @@ -299,10 +277,10 @@ static void dump_node(struct radix_tree_node *node, unsigned long index) } else if (!radix_tree_is_internal_node(entry)) { pr_debug("radix entry %p offset %ld indices %lu-%lu parent %p\n", entry, i, first, last, node); - } else if (is_sibling_entry(node, entry)) { + } else if (xa_is_sibling(entry)) { pr_debug("radix sblng %p offset %ld indices %lu-%lu parent %p val %p\n", entry, i, first, last, node, - *(void **)entry_to_node(entry)); + node->slots[xa_to_sibling(entry)]); } else { dump_node(entry_to_node(entry), first); } @@ -872,8 +850,7 @@ static void radix_tree_free_nodes(struct radix_tree_node *node) for (;;) { void *entry = rcu_dereference_raw(child->slots[offset]); - if (radix_tree_is_internal_node(entry) && - !is_sibling_entry(child, entry)) { + if (xa_is_node(entry)) { child = entry_to_node(entry); offset = 0; continue; @@ -895,7 +872,7 @@ static void radix_tree_free_nodes(struct radix_tree_node *node) static inline int insert_entries(struct radix_tree_node *node, void __rcu **slot, void *item, unsigned order, bool replace) { - struct radix_tree_node *child; + void *sibling; unsigned i, n, tag, offset, tags = 0; if (node) { @@ -913,7 +890,7 @@ static inline int insert_entries(struct radix_tree_node *node, offset = offset & ~(n - 1); slot = &node->slots[offset]; } - child = node_to_entry(slot); + sibling = xa_mk_sibling(offset); for (i = 0; i < n; i++) { if (slot[i]) { @@ -930,7 +907,7 @@ static inline int insert_entries(struct radix_tree_node *node, for (i = 0; i < n; i++) { struct radix_tree_node *old = rcu_dereference_raw(slot[i]); if (i) { - rcu_assign_pointer(slot[i], child); + rcu_assign_pointer(slot[i], sibling); for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) if (tags & (1 << tag)) tag_clear(node, tag, offset + i); @@ -940,9 +917,7 @@ static inline int insert_entries(struct radix_tree_node *node, if (tags & (1 << tag)) tag_set(node, tag, offset); } - if (radix_tree_is_internal_node(old) && - !is_sibling_entry(node, old) && - (old != RADIX_TREE_RETRY)) + if (xa_is_node(old)) radix_tree_free_nodes(old); if (xa_is_value(old)) node->exceptional--; @@ -1101,10 +1076,10 @@ static inline void replace_sibling_entries(struct radix_tree_node *node, void __rcu **slot, int count, int exceptional) { #ifdef CONFIG_RADIX_TREE_MULTIORDER - void *ptr = node_to_entry(slot); - unsigned offset = get_slot_offset(node, slot) + 1; + unsigned offset = get_slot_offset(node, slot); + void *ptr = xa_mk_sibling(offset); - while (offset < RADIX_TREE_MAP_SIZE) { + while (++offset < RADIX_TREE_MAP_SIZE) { if (rcu_dereference_raw(node->slots[offset]) != ptr) break; if (count < 0) { @@ -1112,7 +1087,6 @@ static inline void replace_sibling_entries(struct radix_tree_node *node, node->count--; } node->exceptional += exceptional; - offset++; } #endif } @@ -1311,8 +1285,7 @@ int radix_tree_split(struct radix_tree_root *root, unsigned long index, tags |= 1 << tag; for (end = offset + 1; end < RADIX_TREE_MAP_SIZE; end++) { - if (!is_sibling_entry(parent, - rcu_dereference_raw(parent->slots[end]))) + if (!xa_is_sibling(rcu_dereference_raw(parent->slots[end]))) break; for (tag = 0; tag < RADIX_TREE_MAX_TAGS; tag++) if (tags & (1 << tag)) @@ -1608,11 +1581,9 @@ static void set_iter_tags(struct radix_tree_iter *iter, static void __rcu **skip_siblings(struct radix_tree_node **nodep, void __rcu **slot, struct radix_tree_iter *iter) { - void *sib = node_to_entry(slot - 1); - while (iter->index < iter->next_index) { *nodep = rcu_dereference_raw(*slot); - if (*nodep && *nodep != sib) + if (*nodep && !xa_is_sibling(*nodep)) return slot; slot++; iter->index = __radix_tree_iter_add(iter, 1); @@ -1763,7 +1734,7 @@ void __rcu **radix_tree_next_chunk(const struct radix_tree_root *root, while (++offset < RADIX_TREE_MAP_SIZE) { void *slot = rcu_dereference_raw( node->slots[offset]); - if (is_sibling_entry(node, slot)) + if (xa_is_sibling(slot)) continue; if (slot) break; -- 2.15.0