[04/11] maple_tree: Introduce interfaces __mt_dup() and mt_dup()

  Introduce interfaces __mt_dup() and mt_dup(), which are used to
duplicate a maple tree. Compared with traversing the source tree and
reinserting entry by entry in the new tree, it has better performance.
The difference between __mt_dup() and mt_dup() is that mt_dup() holds
an internal lock.

Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
---
 include/linux/maple_tree.h |   3 +
 lib/maple_tree.c           | 211 +++++++++++++++++++++++++++++++++++++
 2 files changed, 214 insertions(+)
  

* Peng Zhang <zhangpeng.00@bytedance.com> [230726 04:10]:
> Introduce interfaces __mt_dup() and mt_dup(), which are used to
> duplicate a maple tree. Compared with traversing the source tree and
> reinserting entry by entry in the new tree, it has better performance.
> The difference between __mt_dup() and mt_dup() is that mt_dup() holds
> an internal lock.
> 
> Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
> ---
>  include/linux/maple_tree.h |   3 +
>  lib/maple_tree.c           | 211 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 214 insertions(+)
> 
> diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
> index c962af188681..229fe78e4c89 100644
> --- a/include/linux/maple_tree.h
> +++ b/include/linux/maple_tree.h
> @@ -327,6 +327,9 @@ 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 mt_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 da3a2fb405c0..efac6761ae37 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -6595,6 +6595,217 @@ void *mtree_erase(struct maple_tree *mt, unsigned long index)
>  }
>  EXPORT_SYMBOL(mtree_erase);
>  
> +/*
> + * mt_dup_free() - Free the nodes of a incomplete maple tree.
> + * @mt: The incomplete maple tree
> + * @node: Free nodes from @node
> + *
> + * This function frees all nodes starting from @node in the reverse order of
> + * mt_dup_build(). At this point we don't need to hold the source tree lock.
> + */
> +static void mt_dup_free(struct maple_tree *mt, struct maple_node *node)
> +{
> +	void **slots;
> +	unsigned char offset;
> +	struct maple_enode *enode;
> +	enum maple_type type;
> +	unsigned char count = 0, i;
> +

Can we make these labels inline functions and try to make this a loop?

> +try_ascend:
> +	if (ma_is_root(node)) {
> +		mt_free_one(node);
> +		return;
> +	}
> +
> +	offset = ma_parent_slot(node);
> +	type = ma_parent_type(mt, node);
> +	node = ma_parent(node);
> +	if (!offset)
> +		goto free;
> +
> +	offset--;
> +
> +descend:
> +	slots = (void **)ma_slots(node, type);
> +	enode = slots[offset];
> +	if (mte_is_leaf(enode))
> +		goto free;
> +
> +	type = mte_node_type(enode);
> +	node = mte_to_node(enode);
> +	offset = ma_nonleaf_data_end_nocheck(node, type);
> +	goto descend;
> +
> +free:
> +	slots = (void **)ma_slots(node, type);
> +	count = ma_nonleaf_data_end_nocheck(node, type) + 1;
> +	for (i = 0; i < count; i++)
> +		((unsigned long *)slots)[i] &= ~MAPLE_NODE_MASK;
> +
> +	/* Cast to __rcu to avoid sparse checker complaining. */
> +	mt_free_bulk(count, (void __rcu **)slots);
> +	goto try_ascend;
> +}
> +
> +/*
> + * mt_dup_build() - Build a new maple tree from a source tree
> + * @mt: The source maple tree to copy from
> + * @new: The new maple tree
> + * @gfp: The GFP_FLAGS to use for allocations
> + * @to_free: Free nodes starting from @to_free if the build fails
> + *
> + * This function builds a new tree in DFS preorder. If it fails due to memory
> + * allocation, @to_free will store the last failed node to free the incomplete
> + * tree. Use mt_dup_free() to free nodes.
> + *
> + * Return: 0 on success, -ENOMEM if memory could not be allocated.
> + */
> +static inline int mt_dup_build(struct maple_tree *mt, struct maple_tree *new,
> +			       gfp_t gfp, struct maple_node **to_free)

I am trying to change the functions to be two tabs of indent for
arguments from now on.  It allows for more to fit on a single line and
still maintains a clear separation between code and argument lists.

> +{
> +	struct maple_enode *enode;
> +	struct maple_node *new_node, *new_parent = NULL, *node;
> +	enum maple_type type;
> +	void __rcu **slots;
> +	void **new_slots;
> +	unsigned char count, request, i, offset;
> +	unsigned long *set_parent;
> +	unsigned long new_root;
> +
> +	mt_init_flags(new, mt->ma_flags);
> +	enode = mt_root_locked(mt);
> +	if (unlikely(!xa_is_node(enode))) {
> +		rcu_assign_pointer(new->ma_root, enode);
> +		return 0;
> +	}
> +
> +	new_node = mt_alloc_one(gfp);
> +	if (!new_node)
> +		return -ENOMEM;
> +
> +	new_root = (unsigned long)new_node;
> +	new_root |= (unsigned long)enode & MAPLE_NODE_MASK;
> +
> +copy_node:

Can you make copy_node, descend, ascend inline functions instead of the
goto jumping please?  It's better to have loops over jumping around a
lot.  Gotos are good for undoing things and retry, but constructing
loops with them makes it difficult to follow.

> +	node = mte_to_node(enode);
> +	type = mte_node_type(enode);
> +	memcpy(new_node, node, sizeof(struct maple_node));
> +
> +	set_parent = (unsigned long *)&(new_node->parent);
> +	*set_parent &= MAPLE_NODE_MASK;
> +	*set_parent |= (unsigned long)new_parent;

Maybe make a small inline to set the parent instead of this?

There are some defined helpers for setting the types like
ma_parent_ptr() and ma_enode_ptr() to make casting more type-safe.

> +	if (ma_is_leaf(type))
> +		goto ascend;
> +
> +	new_slots = (void **)ma_slots(new_node, type);
> +	slots = ma_slots(node, type);
> +	request = ma_nonleaf_data_end(mt, node, type) + 1;
> +	count = mt_alloc_bulk(gfp, request, new_slots);
> +	if (!count) {
> +		*to_free = new_node;
> +		return -ENOMEM;
> +	}
> +
> +	for (i = 0; i < count; i++)
> +		((unsigned long *)new_slots)[i] |=
> +				((unsigned long)mt_slot_locked(mt, slots, i) &
> +				 MAPLE_NODE_MASK);
> +	offset = 0;
> +
> +descend:
> +	new_parent = new_node;
> +	enode = mt_slot_locked(mt, slots, offset);
> +	new_node = mte_to_node(new_slots[offset]);
> +	goto copy_node;
> +
> +ascend:
> +	if (ma_is_root(node)) {
> +		new_node = mte_to_node((void *)new_root);
> +		new_node->parent = ma_parent_ptr((unsigned long)new |
> +						 MA_ROOT_PARENT);
> +		rcu_assign_pointer(new->ma_root, (void *)new_root);
> +		return 0;
> +	}
> +
> +	offset = ma_parent_slot(node);
> +	type = ma_parent_type(mt, node);
> +	node = ma_parent(node);
> +	new_node = ma_parent(new_node);
> +	if (offset < ma_nonleaf_data_end(mt, node, type)) {
> +		offset++;
> +		new_slots = (void **)ma_slots(new_node, type);
> +		slots = ma_slots(node, type);
> +		goto descend;
> +	}
> +
> +	goto ascend;
> +}
> +
> +/**
> + * __mt_dup(): Duplicate a 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 using a faster method than traversing
> + * the source tree and inserting entries into the new tree one by one. The user
> + * needs to lock the source tree manually. Before calling this function, @new
> + * must be an empty tree or an uninitialized tree. If @mt uses an external lock,
> + * we may also need to manually set @new's external lock using
> + * mt_set_external_lock().
> + *
> + * Return: 0 on success, -ENOMEM if memory could not be allocated.
> + */
> +int __mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp)

We use mas_ for things that won't handle the locking and pass in a maple
state.  Considering the leaves need to be altered once this is returned,
I would expect passing in a maple state should be feasible?

> +{
> +	int ret;
> +	struct maple_node *to_free = NULL;
> +
> +	ret = mt_dup_build(mt, new, gfp, &to_free);
> +
> +	if (unlikely(ret == -ENOMEM)) {

On other errors, will the half constructed tree be returned?  Is this
safe?

> +		if (to_free)
> +			mt_dup_free(new, to_free);
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(__mt_dup);
> +
> +/**
> + * mt_dup(): Duplicate a 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 using a faster method than traversing
> + * the source tree and inserting entries into the new tree one by one. The
> + * function will lock the source tree with an internal lock, and the user does
> + * not need to manually handle the lock. Before calling this function, @new must
> + * be an empty tree or an uninitialized tree. If @mt uses an external lock, we
> + * may also need to manually set @new's external lock using
> + * mt_set_external_lock().
> + *
> + * Return: 0 on success, -ENOMEM if memory could not be allocated.
> + */
> +int mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp)

mtree_ ususually used to indicate locking is handled.

> +{
> +	int ret;
> +	struct maple_node *to_free = NULL;
> +
> +	mtree_lock(mt);
> +	ret = mt_dup_build(mt, new, gfp, &to_free);
> +	mtree_unlock(mt);
> +
> +	if (unlikely(ret == -ENOMEM)) {
> +		if (to_free)
> +			mt_dup_free(new, to_free);

Again, is a half constructed tree safe to return?  Since each caller
checks to_free is NULL, could that be in mt_dup_free() instead?

> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL(mt_dup);
> +
>  /**
>   * __mt_destroy() - Walk and free all nodes of a locked maple tree.
>   * @mt: The maple tree
> -- 
> 2.20.1
> 
>
  

在 2023/7/27 00:03, Liam R. Howlett 写道:
> * Peng Zhang <zhangpeng.00@bytedance.com> [230726 04:10]:
>> Introduce interfaces __mt_dup() and mt_dup(), which are used to
>> duplicate a maple tree. Compared with traversing the source tree and
>> reinserting entry by entry in the new tree, it has better performance.
>> The difference between __mt_dup() and mt_dup() is that mt_dup() holds
>> an internal lock.
>>
>> Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
>> ---
>>   include/linux/maple_tree.h |   3 +
>>   lib/maple_tree.c           | 211 +++++++++++++++++++++++++++++++++++++
>>   2 files changed, 214 insertions(+)
>>
>> diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
>> index c962af188681..229fe78e4c89 100644
>> --- a/include/linux/maple_tree.h
>> +++ b/include/linux/maple_tree.h
>> @@ -327,6 +327,9 @@ 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 mt_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 da3a2fb405c0..efac6761ae37 100644
>> --- a/lib/maple_tree.c
>> +++ b/lib/maple_tree.c
>> @@ -6595,6 +6595,217 @@ void *mtree_erase(struct maple_tree *mt, unsigned long index)
>>   }
>>   EXPORT_SYMBOL(mtree_erase);
>>   
>> +/*
>> + * mt_dup_free() - Free the nodes of a incomplete maple tree.
>> + * @mt: The incomplete maple tree
>> + * @node: Free nodes from @node
>> + *
>> + * This function frees all nodes starting from @node in the reverse order of
>> + * mt_dup_build(). At this point we don't need to hold the source tree lock.
>> + */
>> +static void mt_dup_free(struct maple_tree *mt, struct maple_node *node)
>> +{
>> +	void **slots;
>> +	unsigned char offset;
>> +	struct maple_enode *enode;
>> +	enum maple_type type;
>> +	unsigned char count = 0, i;
>> +
> 
> Can we make these labels inline functions and try to make this a loop?
I did this just to make things easier. Refer to the implementation of
walk_tg_tree_from() in sched/core.c. Using some loops and inline
functions probably doesn't simplify things. I'll try to do that and give
up if it complicates things.
> 
>> +try_ascend:
>> +	if (ma_is_root(node)) {
>> +		mt_free_one(node);
>> +		return;
>> +	}
>> +
>> +	offset = ma_parent_slot(node);
>> +	type = ma_parent_type(mt, node);
>> +	node = ma_parent(node);
>> +	if (!offset)
>> +		goto free;
>> +
>> +	offset--;
>> +
>> +descend:
>> +	slots = (void **)ma_slots(node, type);
>> +	enode = slots[offset];
>> +	if (mte_is_leaf(enode))
>> +		goto free;
>> +
>> +	type = mte_node_type(enode);
>> +	node = mte_to_node(enode);
>> +	offset = ma_nonleaf_data_end_nocheck(node, type);
>> +	goto descend;
>> +
>> +free:
>> +	slots = (void **)ma_slots(node, type);
>> +	count = ma_nonleaf_data_end_nocheck(node, type) + 1;
>> +	for (i = 0; i < count; i++)
>> +		((unsigned long *)slots)[i] &= ~MAPLE_NODE_MASK;
>> +
>> +	/* Cast to __rcu to avoid sparse checker complaining. */
>> +	mt_free_bulk(count, (void __rcu **)slots);
>> +	goto try_ascend;
>> +}
>> +
>> +/*
>> + * mt_dup_build() - Build a new maple tree from a source tree
>> + * @mt: The source maple tree to copy from
>> + * @new: The new maple tree
>> + * @gfp: The GFP_FLAGS to use for allocations
>> + * @to_free: Free nodes starting from @to_free if the build fails
>> + *
>> + * This function builds a new tree in DFS preorder. If it fails due to memory
>> + * allocation, @to_free will store the last failed node to free the incomplete
>> + * tree. Use mt_dup_free() to free nodes.
>> + *
>> + * Return: 0 on success, -ENOMEM if memory could not be allocated.
>> + */
>> +static inline int mt_dup_build(struct maple_tree *mt, struct maple_tree *new,
>> +			       gfp_t gfp, struct maple_node **to_free)
> 
> I am trying to change the functions to be two tabs of indent for
> arguments from now on.  It allows for more to fit on a single line and
> still maintains a clear separation between code and argument lists.
I'm not too concerned about code formatting. . . At least in this
patchset.
> 
>> +{
>> +	struct maple_enode *enode;
>> +	struct maple_node *new_node, *new_parent = NULL, *node;
>> +	enum maple_type type;
>> +	void __rcu **slots;
>> +	void **new_slots;
>> +	unsigned char count, request, i, offset;
>> +	unsigned long *set_parent;
>> +	unsigned long new_root;
>> +
>> +	mt_init_flags(new, mt->ma_flags);
>> +	enode = mt_root_locked(mt);
>> +	if (unlikely(!xa_is_node(enode))) {
>> +		rcu_assign_pointer(new->ma_root, enode);
>> +		return 0;
>> +	}
>> +
>> +	new_node = mt_alloc_one(gfp);
>> +	if (!new_node)
>> +		return -ENOMEM;
>> +
>> +	new_root = (unsigned long)new_node;
>> +	new_root |= (unsigned long)enode & MAPLE_NODE_MASK;
>> +
>> +copy_node:
> 
> Can you make copy_node, descend, ascend inline functions instead of the
> goto jumping please?  It's better to have loops over jumping around a
> lot.  Gotos are good for undoing things and retry, but constructing
> loops with them makes it difficult to follow.
Same as above.
> 
>> +	node = mte_to_node(enode);
>> +	type = mte_node_type(enode);
>> +	memcpy(new_node, node, sizeof(struct maple_node));
>> +
>> +	set_parent = (unsigned long *)&(new_node->parent);
>> +	*set_parent &= MAPLE_NODE_MASK;
>> +	*set_parent |= (unsigned long)new_parent;
> 
> Maybe make a small inline to set the parent instead of this?
> 
> There are some defined helpers for setting the types like
> ma_parent_ptr() and ma_enode_ptr() to make casting more type-safe.
Ok, I'll try to do that.
> 
>> +	if (ma_is_leaf(type))
>> +		goto ascend;
>> +
>> +	new_slots = (void **)ma_slots(new_node, type);
>> +	slots = ma_slots(node, type);
>> +	request = ma_nonleaf_data_end(mt, node, type) + 1;
>> +	count = mt_alloc_bulk(gfp, request, new_slots);
>> +	if (!count) {
>> +		*to_free = new_node;
>> +		return -ENOMEM;
>> +	}
>> +
>> +	for (i = 0; i < count; i++)
>> +		((unsigned long *)new_slots)[i] |=
>> +				((unsigned long)mt_slot_locked(mt, slots, i) &
>> +				 MAPLE_NODE_MASK);
>> +	offset = 0;
>> +
>> +descend:
>> +	new_parent = new_node;
>> +	enode = mt_slot_locked(mt, slots, offset);
>> +	new_node = mte_to_node(new_slots[offset]);
>> +	goto copy_node;
>> +
>> +ascend:
>> +	if (ma_is_root(node)) {
>> +		new_node = mte_to_node((void *)new_root);
>> +		new_node->parent = ma_parent_ptr((unsigned long)new |
>> +						 MA_ROOT_PARENT);
>> +		rcu_assign_pointer(new->ma_root, (void *)new_root);
>> +		return 0;
>> +	}
>> +
>> +	offset = ma_parent_slot(node);
>> +	type = ma_parent_type(mt, node);
>> +	node = ma_parent(node);
>> +	new_node = ma_parent(new_node);
>> +	if (offset < ma_nonleaf_data_end(mt, node, type)) {
>> +		offset++;
>> +		new_slots = (void **)ma_slots(new_node, type);
>> +		slots = ma_slots(node, type);
>> +		goto descend;
>> +	}
>> +
>> +	goto ascend;
>> +}
>> +
>> +/**
>> + * __mt_dup(): Duplicate a 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 using a faster method than traversing
>> + * the source tree and inserting entries into the new tree one by one. The user
>> + * needs to lock the source tree manually. Before calling this function, @new
>> + * must be an empty tree or an uninitialized tree. If @mt uses an external lock,
>> + * we may also need to manually set @new's external lock using
>> + * mt_set_external_lock().
>> + *
>> + * Return: 0 on success, -ENOMEM if memory could not be allocated.
>> + */
>> +int __mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp)
> 
> We use mas_ for things that won't handle the locking and pass in a maple
> state.  Considering the leaves need to be altered once this is returned,
> I would expect passing in a maple state should be feasible?
But we don't really need mas here. What do you think the state of mas
should be when this function returns? Make it point to the first entry,
or the last entry?
> 
>> +{
>> +	int ret;
>> +	struct maple_node *to_free = NULL;
>> +
>> +	ret = mt_dup_build(mt, new, gfp, &to_free);
>> +
>> +	if (unlikely(ret == -ENOMEM)) {
> 
> On other errors, will the half constructed tree be returned?  Is this
> safe?
Of course, mt_dup_free() is carefully designed to handle this.
> 
>> +		if (to_free)
>> +			mt_dup_free(new, to_free);
>> +	}
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL(__mt_dup);
>> +
>> +/**
>> + * mt_dup(): Duplicate a 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 using a faster method than traversing
>> + * the source tree and inserting entries into the new tree one by one. The
>> + * function will lock the source tree with an internal lock, and the user does
>> + * not need to manually handle the lock. Before calling this function, @new must
>> + * be an empty tree or an uninitialized tree. If @mt uses an external lock, we
>> + * may also need to manually set @new's external lock using
>> + * mt_set_external_lock().
>> + *
>> + * Return: 0 on success, -ENOMEM if memory could not be allocated.
>> + */
>> +int mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp)
> 
> mtree_ ususually used to indicate locking is handled.
Before unifying mtree_* and mt_*, I don't think I can see any difference
between them. At least mt_set_in_rcu() and mt_clear_in_rcu() will hold
the lock.
> 
>> +{
>> +	int ret;
>> +	struct maple_node *to_free = NULL;
>> +
>> +	mtree_lock(mt);
>> +	ret = mt_dup_build(mt, new, gfp, &to_free);
>> +	mtree_unlock(mt);
>> +
>> +	if (unlikely(ret == -ENOMEM)) {
>> +		if (to_free)
>> +			mt_dup_free(new, to_free);
> 
> Again, is a half constructed tree safe to return?  Since each caller
> checks to_free is NULL, could that be in mt_dup_free() instead?
Yes, this check can be put in mt_dup_free().
> 
>> +	}
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL(mt_dup);
>> +
>>   /**
>>    * __mt_destroy() - Walk and free all nodes of a locked maple tree.
>>    * @mt: The maple tree
>> -- 
>> 2.20.1
>>
>>
  

* Peng Zhang <zhangpeng.00@bytedance.com> [230731 08:24]:
> 
> 
> 在 2023/7/27 00:03, Liam R. Howlett 写道:
> > * Peng Zhang <zhangpeng.00@bytedance.com> [230726 04:10]:
> > > Introduce interfaces __mt_dup() and mt_dup(), which are used to
> > > duplicate a maple tree. Compared with traversing the source tree and
> > > reinserting entry by entry in the new tree, it has better performance.
> > > The difference between __mt_dup() and mt_dup() is that mt_dup() holds
> > > an internal lock.
> > > 
> > > Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
> > > ---
> > >   include/linux/maple_tree.h |   3 +
> > >   lib/maple_tree.c           | 211 +++++++++++++++++++++++++++++++++++++
> > >   2 files changed, 214 insertions(+)
> > > 
> > > diff --git a/include/linux/maple_tree.h b/include/linux/maple_tree.h
> > > index c962af188681..229fe78e4c89 100644
> > > --- a/include/linux/maple_tree.h
> > > +++ b/include/linux/maple_tree.h
> > > @@ -327,6 +327,9 @@ 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 mt_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 da3a2fb405c0..efac6761ae37 100644
> > > --- a/lib/maple_tree.c
> > > +++ b/lib/maple_tree.c
> > > @@ -6595,6 +6595,217 @@ void *mtree_erase(struct maple_tree *mt, unsigned long index)
> > >   }
> > >   EXPORT_SYMBOL(mtree_erase);
> > > +/*
> > > + * mt_dup_free() - Free the nodes of a incomplete maple tree.
> > > + * @mt: The incomplete maple tree
> > > + * @node: Free nodes from @node
> > > + *
> > > + * This function frees all nodes starting from @node in the reverse order of
> > > + * mt_dup_build(). At this point we don't need to hold the source tree lock.
> > > + */
> > > +static void mt_dup_free(struct maple_tree *mt, struct maple_node *node)
> > > +{
> > > +	void **slots;
> > > +	unsigned char offset;
> > > +	struct maple_enode *enode;
> > > +	enum maple_type type;
> > > +	unsigned char count = 0, i;
> > > +
> > 
> > Can we make these labels inline functions and try to make this a loop?
> I did this just to make things easier. Refer to the implementation of
> walk_tg_tree_from() in sched/core.c. Using some loops and inline
> functions probably doesn't simplify things. I'll try to do that and give
> up if it complicates things.

Thanks, I'd like to try and simplify the code instead of adding goto
label loops. The code you are referencing is from 2008 and goto loops
are not common.

> > 
> > > +try_ascend:
> > > +	if (ma_is_root(node)) {
> > > +		mt_free_one(node);
> > > +		return;
> > > +	}
> > > +
> > > +	offset = ma_parent_slot(node);
> > > +	type = ma_parent_type(mt, node);
> > > +	node = ma_parent(node);
> > > +	if (!offset)
> > > +		goto free;
> > > +
> > > +	offset--;
> > > +
> > > +descend:
> > > +	slots = (void **)ma_slots(node, type);
> > > +	enode = slots[offset];
> > > +	if (mte_is_leaf(enode))
> > > +		goto free;
> > > +
> > > +	type = mte_node_type(enode);
> > > +	node = mte_to_node(enode);
> > > +	offset = ma_nonleaf_data_end_nocheck(node, type);
> > > +	goto descend;
> > > +
> > > +free:
> > > +	slots = (void **)ma_slots(node, type);
> > > +	count = ma_nonleaf_data_end_nocheck(node, type) + 1;
> > > +	for (i = 0; i < count; i++)
> > > +		((unsigned long *)slots)[i] &= ~MAPLE_NODE_MASK;
> > > +
> > > +	/* Cast to __rcu to avoid sparse checker complaining. */
> > > +	mt_free_bulk(count, (void __rcu **)slots);
> > > +	goto try_ascend;
> > > +}
> > > +
> > > +/*
> > > + * mt_dup_build() - Build a new maple tree from a source tree
> > > + * @mt: The source maple tree to copy from
> > > + * @new: The new maple tree
> > > + * @gfp: The GFP_FLAGS to use for allocations
> > > + * @to_free: Free nodes starting from @to_free if the build fails
> > > + *
> > > + * This function builds a new tree in DFS preorder. If it fails due to memory
> > > + * allocation, @to_free will store the last failed node to free the incomplete
> > > + * tree. Use mt_dup_free() to free nodes.
> > > + *
> > > + * Return: 0 on success, -ENOMEM if memory could not be allocated.
> > > + */
> > > +static inline int mt_dup_build(struct maple_tree *mt, struct maple_tree *new,
> > > +			       gfp_t gfp, struct maple_node **to_free)
> > 
> > I am trying to change the functions to be two tabs of indent for
> > arguments from now on.  It allows for more to fit on a single line and
> > still maintains a clear separation between code and argument lists.
> I'm not too concerned about code formatting. . . At least in this
> patchset.

I have a mess of it in the tree and wanted to communicate my desire to
shift to using two tabs for extra arguments in the future.

> > 
> > > +{
> > > +	struct maple_enode *enode;
> > > +	struct maple_node *new_node, *new_parent = NULL, *node;
> > > +	enum maple_type type;
> > > +	void __rcu **slots;
> > > +	void **new_slots;
> > > +	unsigned char count, request, i, offset;
> > > +	unsigned long *set_parent;
> > > +	unsigned long new_root;
> > > +
> > > +	mt_init_flags(new, mt->ma_flags);
> > > +	enode = mt_root_locked(mt);
> > > +	if (unlikely(!xa_is_node(enode))) {
> > > +		rcu_assign_pointer(new->ma_root, enode);
> > > +		return 0;
> > > +	}
> > > +
> > > +	new_node = mt_alloc_one(gfp);
> > > +	if (!new_node)
> > > +		return -ENOMEM;
> > > +
> > > +	new_root = (unsigned long)new_node;
> > > +	new_root |= (unsigned long)enode & MAPLE_NODE_MASK;
> > > +
> > > +copy_node:
> > 
> > Can you make copy_node, descend, ascend inline functions instead of the
> > goto jumping please?  It's better to have loops over jumping around a
> > lot.  Gotos are good for undoing things and retry, but constructing
> > loops with them makes it difficult to follow.
> Same as above.
> > 
> > > +	node = mte_to_node(enode);
> > > +	type = mte_node_type(enode);
> > > +	memcpy(new_node, node, sizeof(struct maple_node));
> > > +
> > > +	set_parent = (unsigned long *)&(new_node->parent);
> > > +	*set_parent &= MAPLE_NODE_MASK;
> > > +	*set_parent |= (unsigned long)new_parent;
> > 
> > Maybe make a small inline to set the parent instead of this?
> > 
> > There are some defined helpers for setting the types like
> > ma_parent_ptr() and ma_enode_ptr() to make casting more type-safe.
> Ok, I'll try to do that.
> > 
> > > +	if (ma_is_leaf(type))
> > > +		goto ascend;
> > > +
> > > +	new_slots = (void **)ma_slots(new_node, type);
> > > +	slots = ma_slots(node, type);
> > > +	request = ma_nonleaf_data_end(mt, node, type) + 1;
> > > +	count = mt_alloc_bulk(gfp, request, new_slots);
> > > +	if (!count) {
> > > +		*to_free = new_node;
> > > +		return -ENOMEM;
> > > +	}
> > > +
> > > +	for (i = 0; i < count; i++)
> > > +		((unsigned long *)new_slots)[i] |=
> > > +				((unsigned long)mt_slot_locked(mt, slots, i) &
> > > +				 MAPLE_NODE_MASK);
> > > +	offset = 0;
> > > +
> > > +descend:
> > > +	new_parent = new_node;
> > > +	enode = mt_slot_locked(mt, slots, offset);
> > > +	new_node = mte_to_node(new_slots[offset]);
> > > +	goto copy_node;
> > > +
> > > +ascend:
> > > +	if (ma_is_root(node)) {
> > > +		new_node = mte_to_node((void *)new_root);
> > > +		new_node->parent = ma_parent_ptr((unsigned long)new |
> > > +						 MA_ROOT_PARENT);
> > > +		rcu_assign_pointer(new->ma_root, (void *)new_root);
> > > +		return 0;
> > > +	}
> > > +
> > > +	offset = ma_parent_slot(node);
> > > +	type = ma_parent_type(mt, node);
> > > +	node = ma_parent(node);
> > > +	new_node = ma_parent(new_node);
> > > +	if (offset < ma_nonleaf_data_end(mt, node, type)) {
> > > +		offset++;
> > > +		new_slots = (void **)ma_slots(new_node, type);
> > > +		slots = ma_slots(node, type);
> > > +		goto descend;
> > > +	}
> > > +
> > > +	goto ascend;
> > > +}
> > > +
> > > +/**
> > > + * __mt_dup(): Duplicate a 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 using a faster method than traversing
> > > + * the source tree and inserting entries into the new tree one by one. The user
> > > + * needs to lock the source tree manually. Before calling this function, @new
> > > + * must be an empty tree or an uninitialized tree. If @mt uses an external lock,
> > > + * we may also need to manually set @new's external lock using
> > > + * mt_set_external_lock().
> > > + *
> > > + * Return: 0 on success, -ENOMEM if memory could not be allocated.
> > > + */
> > > +int __mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp)
> > 
> > We use mas_ for things that won't handle the locking and pass in a maple
> > state.  Considering the leaves need to be altered once this is returned,
> > I would expect passing in a maple state should be feasible?
> But we don't really need mas here. What do you think the state of mas
> should be when this function returns? Make it point to the first entry,
> or the last entry?

I would write it to point to the first element so that the call to
replace the first element can just do that without an extra walk and
document the maple state end point.

> > 
> > > +{
> > > +	int ret;
> > > +	struct maple_node *to_free = NULL;
> > > +
> > > +	ret = mt_dup_build(mt, new, gfp, &to_free);
> > > +
> > > +	if (unlikely(ret == -ENOMEM)) {
> > 
> > On other errors, will the half constructed tree be returned?  Is this
> > safe?
> Of course, mt_dup_free() is carefully designed to handle this.
> > 
> > > +		if (to_free)
> > > +			mt_dup_free(new, to_free);
> > > +	}
> > > +
> > > +	return ret;
> > > +}
> > > +EXPORT_SYMBOL(__mt_dup);
> > > +
> > > +/**
> > > + * mt_dup(): Duplicate a 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 using a faster method than traversing
> > > + * the source tree and inserting entries into the new tree one by one. The
> > > + * function will lock the source tree with an internal lock, and the user does
> > > + * not need to manually handle the lock. Before calling this function, @new must
> > > + * be an empty tree or an uninitialized tree. If @mt uses an external lock, we
> > > + * may also need to manually set @new's external lock using
> > > + * mt_set_external_lock().
> > > + *
> > > + * Return: 0 on success, -ENOMEM if memory could not be allocated.
> > > + */
> > > +int mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp)
> > 
> > mtree_ ususually used to indicate locking is handled.
> Before unifying mtree_* and mt_*, I don't think I can see any difference
> between them. At least mt_set_in_rcu() and mt_clear_in_rcu() will hold
> the lock.

Fair enough.  I was thinking this closely matches __mt_destroy() and
mtree_destroy().  We could be consistent in our inconsistency, at least.

> > 
> > > +{
> > > +	int ret;
> > > +	struct maple_node *to_free = NULL;
> > > +
> > > +	mtree_lock(mt);
> > > +	ret = mt_dup_build(mt, new, gfp, &to_free);
> > > +	mtree_unlock(mt);
> > > +
> > > +	if (unlikely(ret == -ENOMEM)) {
> > > +		if (to_free)
> > > +			mt_dup_free(new, to_free);
> > 
> > Again, is a half constructed tree safe to return?  Since each caller
> > checks to_free is NULL, could that be in mt_dup_free() instead?
> Yes, this check can be put in mt_dup_free().
> > 
> > > +	}
> > > +
> > > +	return ret;
> > > +}
> > > +EXPORT_SYMBOL(mt_dup);
> > > +
> > >   /**
> > >    * __mt_destroy() - Walk and free all nodes of a locked maple tree.
> > >    * @mt: The maple tree
> > > -- 
> > > 2.20.1
> > > 
> > >
  

* Peng Zhang <zhangpeng.00@bytedance.com> [230816 09:42]:
> 
> 
...

> > > > > +/**
> > > > > + * __mt_dup(): Duplicate a 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 using a faster method than traversing
> > > > > + * the source tree and inserting entries into the new tree one by one. The user
> > > > > + * needs to lock the source tree manually. Before calling this function, @new
> > > > > + * must be an empty tree or an uninitialized tree. If @mt uses an external lock,
> > > > > + * we may also need to manually set @new's external lock using
> > > > > + * mt_set_external_lock().
> > > > > + *
> > > > > + * Return: 0 on success, -ENOMEM if memory could not be allocated.
> > > > > + */
> > > > > +int __mt_dup(struct maple_tree *mt, struct maple_tree *new, gfp_t gfp)
> > > > 
> > > > We use mas_ for things that won't handle the locking and pass in a maple
> > > > state.  Considering the leaves need to be altered once this is returned,
> > > > I would expect passing in a maple state should be feasible?
> > > But we don't really need mas here. What do you think the state of mas
> > > should be when this function returns? Make it point to the first entry,
> > > or the last entry?
> > 
> > I would write it to point to the first element so that the call to
> > replace the first element can just do that without an extra walk and
> > document the maple state end point.
> Unfortunately, this does not seem to be convenient. Users usually use
> mas_for_each() to replace elements. If we set mas to the first element,
> the first call to mas_find() in mas_for_each() will get the next
> element.

This sounds like the need for another iterator specifically for
duplicating.

> 
> There may also be other scenarios where the user does not necessarily
> have to replace every element.

Do you mean a limit or elements that need to be skipped?  We could have
a limit on the iteration.

> 
> Finally, getting the first element in __mt_dup() requires an additional
> check to check whether the first element has already been recorded. Such
> a check will be performed at each leaf node, which is unnecessary
> overhead.
> 
> Of course, the first reason is the main reason, which prevents us from
> using mas_for_each(). So I don't want to record the first element.


I don't like the interface because it can easily be misunderstood and
used incorrectly.  I don't know how to make a cleaner interface, but
I've gone through a few thoughts:

The first was hide _all of it_ in a new iterator:
mas_dup_each(old, new, old_entry) {
	if (don't_dup(old_entry)) {
		mas_erase(new);
		continue;
	}

	mas_dup_insert(new, new_entry);
}

This iterator would check if mas_is_start(old) and dup the tree in that
event.  Leave the both new trees pointing to the first element and set
old_entry.  I don't know how to handle the failure in duplicating the
tree in this case - I guess we could return old_entry = NULL and check
if mas_is_err(old) after the loop.  Do you see a problem with this?


The second idea was an init of the old tree.  This is closest to what you
have:

if (mas_dup_init(old, new))
	goto -ENOMEM;

mas_dup_each(old, new) {
	if (don't_dup(old_entry)) {
		mas_erase(new);
		continue;
	}

	mas_dup_insert(new, new_entry);
}

This would duplicate the tree at the start and leave both pointing at
the first element so that mas_dup_each() could start on that element.
Each subsequent call would go to the next element in both maple states.
It sounds like you don't want this for performance reasons?  Although
looking at mas_find() today, I think this could still work since we are
checking the maple state for a lot.

Both ideas could be even faster than what you have if we handle the
special cases of mas_is_none()/mas_is_ptr() in a smarter way because we
don't need to be as worried about the entry point of the maple state as
much as we do with mas_find()/mas_for_each().  I mean, is it possible to
get to a mas_is_none() or mas_is_ptr() on duplicating a tree?  How do we
handle these users?

Both ideas still suffer from someone saying "Gee, that {insert function
name here} is used in the forking code, so I can totally use that in my
code because that's how it work!"  and find out it works for the limited
testing they do.  Then it fails later and the emails start flying.


I almost think we should do something like this on insert:

void mas_dup_insert(old, new, new_entry) {
	WARN_ON_ONCE(old == new);
	WARN_ON_ONCE(old->index != new->index);
	WARN_ON_ONCE(old->last != new->last);
	...
}

This would at least _require_ someone to have two maple states and
hopefully think twice on using it where it should not be used.

The bottom line is that this code is close to what we need to make
forking better, but I fear the misuse of the interface.

Something else to think about:
In the work items for the Maple Tree, there is a plan to have an enum to
specify the type of write that is going to happen.  The idea was for
mas_preallocate() to set this type of write so we can just go right to
the correct function.  We could use that here and set the maple state
write type to a direct replacement.

Thanks,
Liam