Date: Thu, 13 Jun 2024 10:27:00 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc: linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org, willy@...radead.org
Subject: Re: [PATCH v2 04/16] maple_tree: introduce mas_wr_store_type()

* Sidhartha Kumar <sidhartha.kumar@...cle.com> [240607 14:53]:
> Introduce mas_wr_store_type() which will set the correct store type
> based on a walk of the tree.
> 
> mas_prealloc_calc() is also introduced to abstract the calculation used
> to determine the number of nodes needed for a store operation.
> 
> In this change a call to mas_reset() is removed in the error case of
> mas_prealloc(). This is only needed in the MA_STATE_REBALANCE case of
> mas_destroy(). We can move the call to mas_reset() directly to
> mas_destroy().
> 
> Also, add a test case to validate the order that we check the store type
> in is correct. This test models a vma expanding and then shrinking which
> is part of the boot process.
> 
> Signed-off-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
> ---
>  lib/maple_tree.c                 | 214 ++++++++++++++++++++++---------
>  tools/testing/radix-tree/maple.c |  38 ++++++
>  2 files changed, 192 insertions(+), 60 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 2558d15bb748..a7f585ed488c 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -4278,6 +4278,151 @@ static inline void mas_wr_prealloc_setup(struct ma_wr_state *wr_mas)
>  	wr_mas->content = mas_start(mas);
>  }
>  
> +/**
> + * mas_prealloc_calc() - Calculate number of nodes needed for a
> + * given store oepration
> + * @mas: The maple state
> + * @entry: The entry to store into the tree
> + *
> + * Return: Number of nodes required for preallocation.
> + */
> +static inline int mas_prealloc_calc(struct ma_state *mas, void *entry)
> +{
> +	int ret = mas_mt_height(mas) * 3 + 1;
> +
> +	switch (mas->store_type) {
> +	case wr_invalid:
> +		WARN_ON_ONCE(1);
> +		break;
> +	case wr_new_root:
> +		ret = 1;
> +		break;
> +	case wr_store_root:
> +		if (likely((mas->last != 0) || (mas->index != 0)))
> +			ret = 1;
> +		else if (((unsigned long) (entry) & 3) == 2)
> +			ret = 1;
> +		else
> +			ret = 0;
> +		break;
> +	case wr_spanning_store:
> +		ret =  mas_mt_height(mas) * 3 + 1;
> +		break;
> +	case wr_split_store:
> +		ret =  mas_mt_height(mas) * 2 + 1;
> +		break;
> +	case wr_rebalance:
> +		ret =  mas_mt_height(mas) * 2 - 1;
> +		break;
> +	case wr_node_store:
> +	case wr_bnode:
> +		ret = mt_in_rcu(mas->tree) ? 1 : 0;
> +		break;
> +	case wr_append:
> +	case wr_exact_fit:
> +	case wr_slot_store:
> +		ret = 0;
> +	}
> +
> +	return ret;
> +}
> +
> +/*
> + * mas_wr_store_type() - Set the store type for a given
> + * store operation.
> + * @wr_mas: The maple write state
> + */
> +static inline void mas_wr_store_type(struct ma_wr_state *wr_mas)
> +{
> +	struct ma_state *mas = wr_mas->mas;
> +	unsigned char new_end;
> +
> +	if (unlikely(mas_is_none(mas) || mas_is_ptr(mas))) {
> +		mas->store_type = wr_store_root;
> +		return;
> +	}
> +
> +	if (unlikely(!mas_wr_walk(wr_mas))) {
> +		mas->store_type = wr_spanning_store;
> +		return;
> +	}
> +
> +	/* At this point, we are at the leaf node that needs to be altered. */
> +	mas_wr_end_piv(wr_mas);
> +	if (!wr_mas->entry)
> +		mas_wr_extend_null(wr_mas);
> +
> +	new_end = mas_wr_new_end(wr_mas);
> +	if ((wr_mas->r_min == mas->index) && (wr_mas->r_max == mas->last)) {
> +		mas->store_type = wr_exact_fit;
> +		return;
> +	}
> +
> +	if (unlikely(!mas->index && mas->last == ULONG_MAX)) {
> +		mas->store_type = wr_new_root;
> +		return;
> +	}
> +
> +	/* Potential spanning rebalance collapsing a node */
> +	if (new_end < mt_min_slots[wr_mas->type]) {
> +		if (!mte_is_root(mas->node)) {
> +			mas->store_type = wr_rebalance;
> +			return;
> +		}
> +		mas->store_type = wr_node_store;
> +		return;
> +	}
> +
> +	if (new_end >= mt_slots[wr_mas->type]) {
> +		mas->store_type = wr_split_store;
> +		return;
> +	}
> +
> +	if (!mt_in_rcu(mas->tree) && (mas->offset == mas->end)) {
> +		mas->store_type = wr_append;
> +		return;
> +	}
> +
> +	if ((new_end == mas->end) && (!mt_in_rcu(mas->tree) ||
> +		(wr_mas->offset_end - mas->offset == 1))) {
> +		mas->store_type = wr_slot_store;
> +		return;
> +	}
> +
> +	if (mte_is_root(mas->node) || !(new_end <= mt_min_slots[wr_mas->type]) ||
> +		(mas->mas_flags & MA_STATE_BULK)) {
> +		mas->store_type = wr_node_store;
> +		return;
> +	}
> +
> +	mas->store_type = wr_bnode;
> +}
> +
> +/**
> + * mas_wr_preallocate() - Preallocate enough nodes for a store operation
> + * @wr_mas: The maple write state
> + * @entry: The entry that will be stored
> + * @gfp: The GFP_FLAGS to use for allocations.
> + *
> + */
> +static inline void mas_wr_preallocate(struct ma_wr_state *wr_mas, void *entry, gfp_t gfp)
> +{
> +	struct ma_state *mas = wr_mas->mas;
> +	int request;
> +
> +	mas_wr_prealloc_setup(wr_mas);
> +	mas_wr_store_type(wr_mas);
> +	request = mas_prealloc_calc(mas, entry);
> +	if (!request)
> +		return;
> +
> +	mas_node_count_gfp(mas, request, gfp);
> +	if (likely(!mas_is_err(mas)))
> +		return;
> +
> +	mas_set_alloc_req(mas, 0);
> +}
> +
>  /**
>   * mas_insert() - Internal call to insert a value
>   * @mas: The maple state
> @@ -5506,69 +5651,17 @@ EXPORT_SYMBOL_GPL(mas_store_prealloc);
>  int mas_preallocate(struct ma_state *mas, void *entry, gfp_t gfp)
>  {
>  	MA_WR_STATE(wr_mas, mas, entry);
> -	unsigned char node_size;
> -	int request = 1;
> -	int ret;
> -
> -
> -	if (unlikely(!mas->index && mas->last == ULONG_MAX))
> -		goto ask_now;
> -
> -	mas_wr_prealloc_setup(&wr_mas);
> -	/* Root expand */
> -	if (unlikely(mas_is_none(mas) || mas_is_ptr(mas)))
> -		goto ask_now;
> -
> -	if (unlikely(!mas_wr_walk(&wr_mas))) {
> -		/* Spanning store, use worst case for now */
> -		request = 1 + mas_mt_height(mas) * 3;
> -		goto ask_now;
> -	}
> -
> -	/* At this point, we are at the leaf node that needs to be altered. */
> -	/* Exact fit, no nodes needed. */
> -	if (wr_mas.r_min == mas->index && wr_mas.r_max == mas->last)
> -		return 0;
> -
> -	mas_wr_end_piv(&wr_mas);
> -	node_size = mas_wr_new_end(&wr_mas);
> -
> -	/* Slot store, does not require additional nodes */
> -	if (node_size == mas->end) {
> -		/* reuse node */
> -		if (!mt_in_rcu(mas->tree))
> -			return 0;
> -		/* shifting boundary */
> -		if (wr_mas.offset_end - mas->offset == 1)
> -			return 0;
> -	}
> +	int ret = 0;
>  
> -	if (node_size >= mt_slots[wr_mas.type]) {
> -		/* Split, worst case for now. */
> -		request = 1 + mas_mt_height(mas) * 2;
> -		goto ask_now;
> +	mas_wr_preallocate(&wr_mas, entry, gfp);
> +	if (mas_is_err(mas)) {
> +		ret = xa_err(mas->node);
> +		mas_destroy(mas);
> +		mas_reset(mas);
> +		return ret;
>  	}
>  
> -	/* New root needs a single node */
> -	if (unlikely(mte_is_root(mas->node)))
> -		goto ask_now;
> -
> -	/* Potential spanning rebalance collapsing a node, use worst-case */
> -	if (node_size  - 1 <= mt_min_slots[wr_mas.type])
> -		request = mas_mt_height(mas) * 2 - 1;
> -
> -	/* node store, slot store needs one node */
> -ask_now:
> -	mas_node_count_gfp(mas, request, gfp);
>  	mas->mas_flags |= MA_STATE_PREALLOC;
> -	if (likely(!mas_is_err(mas)))
> -		return 0;
> -
> -	mas_set_alloc_req(mas, 0);
> -	ret = xa_err(mas->node);
> -	mas_reset(mas);
> -	mas_destroy(mas);
> -	mas_reset(mas);
>  	return ret;
>  }
>  EXPORT_SYMBOL_GPL(mas_preallocate);
> @@ -5594,7 +5687,8 @@ void mas_destroy(struct ma_state *mas)
>  	 */
>  	if (mas->mas_flags & MA_STATE_REBALANCE) {
>  		unsigned char end;
> -

nit: This new line should remain.

> +		if (mas_is_err(mas))
> +			mas_reset(mas);
>  		mas_start(mas);
>  		mtree_range_walk(mas);
>  		end = mas->end + 1;
> diff --git a/tools/testing/radix-tree/maple.c b/tools/testing/radix-tree/maple.c
> index f1caf4bcf937..1c68ccc1b475 100644
> --- a/tools/testing/radix-tree/maple.c
> +++ b/tools/testing/radix-tree/maple.c
> @@ -36223,6 +36223,40 @@ static noinline void __init check_mtree_dup(struct maple_tree *mt)
>  
>  extern void test_kmem_cache_bulk(void);
>  
> +

nit: This new line should not be added.

> + /* test to simulate expanding a vma from [0x7fffffffe000, 0x7ffffffff000)
> +  * to [0x7ffde4ca1000, 0x7ffffffff000) and then shrinking the vma to
> +  * [0x7ffde4ca1000, 0x7ffde4ca2000)
> +  */
> +static inline int check_vma_modification(struct maple_tree *mt)
> +{
> +	MA_STATE(mas, mt, 0, 0);
> +
> +	mtree_lock(mt);
> +	/* vma with old start and old end */
> +	__mas_set_range(&mas, 0x7fffffffe000, 0x7ffffffff000 - 1);
> +	mas_preallocate(&mas, xa_mk_value(1), GFP_KERNEL);
> +	mas_store_prealloc(&mas, xa_mk_value(1));
> +
> +	/* next write occurs partly in previous range [0, 0x7fffffffe000)*/
> +	mas_prev_range(&mas, 0);
> +	/* expand vma to {0x7ffde4ca1000, 0x7ffffffff000) */
> +	__mas_set_range(&mas, 0x7ffde4ca1000, 0x7ffffffff000 - 1);
> +	mas_preallocate(&mas, xa_mk_value(1), GFP_KERNEL);
> +	mas_store_prealloc(&mas, xa_mk_value(1));
> +
> +	/* shrink vma to [0x7ffde4ca1000, 7ffde4ca2000) */
> +	__mas_set_range(&mas, 0x7ffde4ca2000, 0x7ffffffff000 - 1);
> +	mas_preallocate(&mas, NULL, GFP_KERNEL);
> +	mas_store_prealloc(&mas, NULL);
> +	mt_dump(mt, mt_dump_hex);
> +
> +	mas_destroy(&mas);
> +	mtree_unlock(mt);
> +	return 0;
> +}
> +
> +

nit: This new line should not be added.

>  void farmer_tests(void)
>  {
>  	struct maple_node *node;
> @@ -36230,6 +36264,10 @@ void farmer_tests(void)
>  
>  	mt_dump(&tree, mt_dump_dec);
>  
> +	mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE | MT_FLAGS_LOCK_EXTERN | MT_FLAGS_USE_RCU);
> +	check_vma_modification(&tree);
> +	mtree_destroy(&tree);
> +
>  	tree.ma_root = xa_mk_value(0);
>  	mt_dump(&tree, mt_dump_dec);
>  
> -- 
> 2.45.2
> 

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