Messages in this thread | | | Date | Tue, 24 Oct 2023 16:40:18 +0800 | Subject | Re: [PATCH v5 03/10] maple_tree: Introduce interfaces __mt_dup() and mtree_dup() | From | Peng Zhang <> |
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在 2023/10/17 21:57, Liam R. Howlett 写道: > * Peng Zhang <zhangpeng.00@bytedance.com> [231015 23:23]: >> Introduce interfaces __mt_dup() and mtree_dup(), which are used to >> duplicate a maple tree. They duplicate a maple tree in Depth-First >> Search (DFS) pre-order traversal. It uses memcopy() to copy nodes in the >> source tree and allocate new child nodes in non-leaf nodes. The new node >> is exactly the same as the source node except for all the addresses >> stored in it. It will be faster than traversing all elements in the >> source tree and inserting them one by one into the new tree. The time >> complexity of these two functions is O(n). >> >> The difference between __mt_dup() and mtree_dup() is that mtree_dup() >> handles locks internally. >> >> Analysis of the average time complexity of this algorithm: >> >> For simplicity, let's assume that the maximum branching factor of all >> non-leaf nodes is 16 (in allocation mode, it is 10), and the tree is a >> full tree. >> >> Under the given conditions, if there is a maple tree with n elements, >> the number of its leaves is n/16. From bottom to top, the number of >> nodes in each level is 1/16 of the number of nodes in the level below. >> So the total number of nodes in the entire tree is given by the sum of >> n/16 + n/16^2 + n/16^3 + ... + 1. This is a geometric series, and it has >> log(n) terms with base 16. According to the formula for the sum of a >> geometric series, the sum of this series can be calculated as (n-1)/15. >> Each node has only one parent node pointer, which can be considered as >> an edge. In total, there are (n-1)/15-1 edges. >> >> This algorithm consists of two operations: >> >> 1. Traversing all nodes in DFS order. >> 2. For each node, making a copy and performing necessary modifications >> to create a new node. >> >> For the first part, DFS traversal will visit each edge twice. Let >> T(ascend) represent the cost of taking one step downwards, and >> T(descend) represent the cost of taking one step upwards. And both of >> them are constants (although mas_ascend() may not be, as it contains a >> loop, but here we ignore it and treat it as a constant). So the time >> spent on the first part can be represented as >> ((n-1)/15-1) * (T(ascend) + T(descend)). >> >> For the second part, each node will be copied, and the cost of copying a >> node is denoted as T(copy_node). For each non-leaf node, it is necessary >> to reallocate all child nodes, and the cost of this operation is denoted >> as T(dup_alloc). The behavior behind memory allocation is complex and >> not specific to the maple tree operation. Here, we assume that the time >> required for a single allocation is constant. Since the size of a node >> is fixed, both of these symbols are also constants. We can calculate >> that the time spent on the second part is >> ((n-1)/15) * T(copy_node) + ((n-1)/15 - n/16) * T(dup_alloc). >> >> Adding both parts together, the total time spent by the algorithm can be >> represented as: >> >> ((n-1)/15) * (T(ascend) + T(descend) + T(copy_node) + T(dup_alloc)) - >> n/16 * T(dup_alloc) - (T(ascend) + T(descend)) >> >> Let C1 = T(ascend) + T(descend) + T(copy_node) + T(dup_alloc) >> Let C2 = T(dup_alloc) >> Let C3 = T(ascend) + T(descend) >> >> Finally, the expression can be simplified as: >> ((16 * C1 - 15 * C2) / (15 * 16)) * n - (C1 / 15 + C3). >> >> This is a linear function, so the average time complexity is O(n). >> >> Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com> >> --- >> include/linux/maple_tree.h | 3 + >> lib/maple_tree.c | 290 +++++++++++++++++++++++++++++++++++++ >> 2 files changed, 293 insertions(+) >> >> diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h >> index f91dbc7fe091..a452dd8a1e5c 100644 >> --- a/include/linux/maple_tree.h >> +++ b/include/linux/maple_tree.h >> @@ -329,6 +329,9 @@ int mtree_store(struct maple_tree *mt, unsigned long index, >> void *entry, gfp_t gfp); >> void *mtree_erase(struct maple_tree *mt, unsigned long index); >> >> +int mtree_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp); >> +int __mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp); >> + >> void mtree_destroy(struct maple_tree *mt); >> void __mt_destroy(struct maple_tree *mt); >> >> diff --git a/lib/maple_tree.c b/lib/maple_tree.c >> index ca7039633844..6e0ad83f14e3 100644 >> --- a/lib/maple_tree.c >> +++ b/lib/maple_tree.c >> @@ -4,6 +4,10 @@ >> * Copyright (c) 2018-2022 Oracle Corporation >> * Authors: Liam R. Howlett <Liam.Howlett@oracle.com> >> * Matthew Wilcox <willy@infradead.org> >> + * >> + * Algorithm for duplicating Maple Tree >> + * Copyright (c) 2023 ByteDance >> + * Author: Peng Zhang <zhangpeng.00@bytedance.com> >> */ >> >> /* >> @@ -6475,6 +6479,292 @@ void *mtree_erase(struct maple_tree *mt, unsigned long index) >> } >> EXPORT_SYMBOL(mtree_erase); >> >> +/* >> + * mas_dup_free() - Free an incomplete duplication of a tree. >> + * @mas: The maple state of a incomplete tree. >> + * >> + * The parameter @mas->node passed in indicates that the allocation failed on >> + * this node. This function frees all nodes starting from @mas->node in the >> + * reverse order of mas_dup_build(). There is no need to hold the source tree >> + * lock at this time. >> + */ >> +static void mas_dup_free(struct ma_state *mas) >> +{ >> + struct maple_node *node; >> + enum maple_type type; >> + void __rcu **slots; >> + unsigned char count, i; >> + >> + /* Maybe the first node allocation failed. */ >> + if (mas_is_none(mas)) >> + return; >> + >> + while (!mte_is_root(mas->node)) { >> + mas_ascend(mas); >> + > > Please watch the extra whitespace. There are a few in this patch. Done in v6, thank you. > >> + if (mas->offset) { >> + mas->offset--; >> + do { >> + mas_descend(mas); >> + mas->offset = mas_data_end(mas); >> + } while (!mte_is_leaf(mas->node)); >> + >> + mas_ascend(mas); >> + } >> + >> + node = mte_to_node(mas->node); >> + type = mte_node_type(mas->node); >> + slots = ma_slots(node, type); >> + count = mas_data_end(mas) + 1; >> + for (i = 0; i < count; i++) >> + ((unsigned long *)slots)[i] &= ~MAPLE_NODE_MASK; >> + >> + mt_free_bulk(count, slots); >> + } >> + >> + node = mte_to_node(mas->node); >> + mt_free_one(node); >> +} >> + >> +/* >> + * mas_copy_node() - Copy a maple node and replace the parent. >> + * @mas: The maple state of source tree. >> + * @new_mas: The maple state of new tree. >> + * @parent: The parent of the new node. >> + * >> + * Copy @mas->node to @new_mas->node, set @parent to be the parent of >> + * @new_mas->node. If memory allocation fails, @mas is set to -ENOMEM. >> + */ >> +static inline void mas_copy_node(struct ma_state *mas, struct ma_state *new_mas, >> + struct maple_pnode *parent) >> +{ >> + struct maple_node *node = mte_to_node(mas->node); >> + struct maple_node *new_node = mte_to_node(new_mas->node); >> + unsigned long val; >> + >> + /* Copy the node completely. */ >> + memcpy(new_node, node, sizeof(struct maple_node)); >> + >> + /* Update the parent node pointer. */ >> + val = (unsigned long)node->parent & MAPLE_NODE_MASK; >> + new_node->parent = ma_parent_ptr(val | (unsigned long)parent); >> +} >> + >> +/* >> + * mas_dup_alloc() - Allocate child nodes for a maple node. >> + * @mas: The maple state of source tree. >> + * @new_mas: The maple state of new tree. >> + * @gfp: The GFP_FLAGS to use for allocations. >> + * >> + * This function allocates child nodes for @new_mas->node during the duplication >> + * process. If memory allocation fails, @mas is set to -ENOMEM. >> + */ >> +static inline void mas_dup_alloc(struct ma_state *mas, struct ma_state *new_mas, >> + gfp_t gfp) >> +{ >> + struct maple_node *node = mte_to_node(mas->node); >> + struct maple_node *new_node = mte_to_node(new_mas->node); >> + enum maple_type type; >> + unsigned char request, count, i; >> + void __rcu **slots; >> + void __rcu **new_slots; >> + unsigned long val; >> + >> + /* Allocate memory for child nodes. */ >> + type = mte_node_type(mas->node); >> + new_slots = ma_slots(new_node, type); >> + request = mas_data_end(mas) + 1; >> + count = mt_alloc_bulk(gfp, request, (void **)new_slots); >> + if (unlikely(count < request)) { >> + if (count) >> + mt_free_bulk(count, new_slots); > > We were dropping this mt_free_bulk() call as discussed in [1]. Did I > miss something? It seems that I misunderstood earlier, I thought it needed to be kept. It has been deleted in v6, thank you. > >> + >> + memset(new_slots, 0, request * sizeof(void *)); >> + mas_set_err(mas, -ENOMEM); >> + return; >> + } >> + >> + /* Restore node type information in slots. */ >> + slots = ma_slots(node, type); >> + for (i = 0; i < count; i++) { >> + val = (unsigned long)mt_slot_locked(mas->tree, slots, i); >> + val &= MAPLE_NODE_MASK; >> + ((unsigned long *)new_slots)[i] |= val; >> + } >> +} >> + >> +/* >> + * mas_dup_build() - Build a new maple tree from a source tree >> + * @mas: The maple state of source tree, need to be in MAS_START state. >> + * @new_mas: The maple state of new tree, need to be in MAS_START state. >> + * @gfp: The GFP_FLAGS to use for allocations. >> + * >> + * This function builds a new tree in DFS preorder. If the memory allocation >> + * fails, the error code -ENOMEM will be set in @mas, and @new_mas points to the >> + * last node. mas_dup_free() will free the incomplete duplication of a tree. >> + * >> + * Note that the attributes of the two trees need to be exactly the same, and the >> + * new tree needs to be empty, otherwise -EINVAL will be set in @mas. >> + */ >> +static inline void mas_dup_build(struct ma_state *mas, struct ma_state *new_mas, >> + gfp_t gfp) >> +{ >> + struct maple_node *node; >> + struct maple_pnode *parent = NULL; >> + struct maple_enode *root; >> + enum maple_type type; >> + >> + if (unlikely(mt_attr(mas->tree) != mt_attr(new_mas->tree)) || >> + unlikely(!mtree_empty(new_mas->tree))) { >> + mas_set_err(mas, -EINVAL); >> + return; >> + } >> + >> + mas_start(mas); >> + if (mas_is_ptr(mas) || mas_is_none(mas)) { >> + root = mt_root_locked(mas->tree); > > mas_start(mas) would return the root entry if it's a pointer and NULL if > the tree is empty, so this can be written: > root = mas_start(mas); > if (mas_is_ptry() || mas_is_none() > goto set_new_tree; Done in v6, thank you. > > >> + goto set_new_tree; >> + } >> + >> + node = mt_alloc_one(gfp); >> + if (!node) { >> + new_mas->node = MAS_NONE; >> + mas_set_err(mas, -ENOMEM); >> + return; >> + } >> + >> + type = mte_node_type(mas->node); >> + root = mt_mk_node(node, type); >> + new_mas->node = root; >> + new_mas->min = 0; >> + new_mas->max = ULONG_MAX; >> + root = mte_mk_root(root); >> + >> + while (1) { >> + mas_copy_node(mas, new_mas, parent); >> + >> + if (!mte_is_leaf(mas->node)) { >> + /* Only allocate child nodes for non-leaf nodes. */ >> + mas_dup_alloc(mas, new_mas, gfp); >> + if (unlikely(mas_is_err(mas))) >> + return; >> + } else { >> + /* >> + * This is the last leaf node and duplication is >> + * completed. >> + */ >> + if (mas->max == ULONG_MAX) >> + goto done; >> + >> + /* This is not the last leaf node and needs to go up. */ >> + do { >> + mas_ascend(mas); >> + mas_ascend(new_mas); >> + } while (mas->offset == mas_data_end(mas)); >> + >> + /* Move to the next subtree. */ >> + mas->offset++; >> + new_mas->offset++; >> + } >> + >> + mas_descend(mas); >> + parent = ma_parent_ptr(mte_to_node(new_mas->node)); >> + mas_descend(new_mas); >> + mas->offset = 0; >> + new_mas->offset = 0; >> + } >> +done: >> + /* Specially handle the parent of the root node. */ >> + mte_to_node(root)->parent = ma_parent_ptr(mas_tree_parent(new_mas)); >> +set_new_tree: >> + /* Make them the same height */ >> + new_mas->tree->ma_flags = mas->tree->ma_flags; >> + rcu_assign_pointer(new_mas->tree->ma_root, root); >> +} >> + >> +/** >> + * __mt_dup(): Duplicate an entire maple tree >> + * @mt: The source maple tree >> + * @new: The new maple tree >> + * @gfp: The GFP_FLAGS to use for allocations >> + * >> + * This function duplicates a maple tree in Depth-First Search (DFS) pre-order >> + * traversal. It uses memcopy() to copy nodes in the source tree and allocate >> + * new child nodes in non-leaf nodes. The new node is exactly the same as the >> + * source node except for all the addresses stored in it. It will be faster than >> + * traversing all elements in the source tree and inserting them one by one into >> + * the new tree. >> + * The user needs to ensure that the attributes of the source tree and the new >> + * tree are the same, and the new tree needs to be an empty tree, otherwise >> + * -EINVAL will be returned. >> + * Note that the user needs to manually lock the source tree and the new tree. >> + * >> + * Return: 0 on success, -ENOMEM if memory could not be allocated, -EINVAL If >> + * the attributes of the two trees are different or the new tree is not an empty >> + * tree. >> + */ >> +int __mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp) >> +{ >> + int ret = 0; >> + MA_STATE(mas, mt, 0, 0); >> + MA_STATE(new_mas, new, 0, 0); >> + >> + mas_dup_build(&mas, &new_mas, gfp); >> + >> + if (unlikely(mas_is_err(&mas))) { >> + ret = xa_err(mas.node); >> + if (ret == -ENOMEM) >> + mas_dup_free(&new_mas); >> + } >> + >> + return ret; >> +} >> +EXPORT_SYMBOL(__mt_dup); >> + >> +/** >> + * mtree_dup(): Duplicate an entire maple tree >> + * @mt: The source maple tree >> + * @new: The new maple tree >> + * @gfp: The GFP_FLAGS to use for allocations >> + * >> + * This function duplicates a maple tree in Depth-First Search (DFS) pre-order >> + * traversal. It uses memcopy() to copy nodes in the source tree and allocate >> + * new child nodes in non-leaf nodes. The new node is exactly the same as the >> + * source node except for all the addresses stored in it. It will be faster than >> + * traversing all elements in the source tree and inserting them one by one into >> + * the new tree. >> + * The user needs to ensure that the attributes of the source tree and the new >> + * tree are the same, and the new tree needs to be an empty tree, otherwise >> + * -EINVAL will be returned. >> + * >> + * Return: 0 on success, -ENOMEM if memory could not be allocated, -EINVAL If >> + * the attributes of the two trees are different or the new tree is not an empty >> + * tree. >> + */ >> +int mtree_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp) >> +{ >> + int ret = 0; >> + MA_STATE(mas, mt, 0, 0); >> + MA_STATE(new_mas, new, 0, 0); >> + >> + mas_lock(&new_mas); >> + mas_lock_nested(&mas, SINGLE_DEPTH_NESTING); >> + >> + mas_dup_build(&mas, &new_mas, gfp); >> + mas_unlock(&mas); >> + >> + if (unlikely(mas_is_err(&mas))) { >> + ret = xa_err(mas.node); >> + if (ret == -ENOMEM) >> + mas_dup_free(&new_mas); >> + } >> + >> + mas_unlock(&new_mas); >> + >> + return ret; >> +} >> +EXPORT_SYMBOL(mtree_dup); >> + >> /** >> * __mt_destroy() - Walk and free all nodes of a locked maple tree. >> * @mt: The maple tree >> -- >> 2.20.1 >> > > [1]. https://lore.kernel.org/lkml/20231004142500.gz2552r74aiphl4z@revolver/ > > Thanks, > Liam
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