Re: [PATCH 26/94] Maple Tree: Add new data structure

[Peter Zijlstra]

Cc'ing a moderated list is sodding annoying, dropped it.

On Wed, Apr 28, 2021 at 03:36:02PM +0000, Liam Howlett wrote:

> +struct maple_range_64 {
> +	struct maple_pnode *parent;
> +	unsigned long pivot[MAPLE_RANGE64_SLOTS - 1];
> +	void __rcu *slot[MAPLE_RANGE64_SLOTS];
> +};
> +
> +struct maple_arange_64 {
> +	struct maple_pnode *parent;
> +	unsigned long pivot[MAPLE_ARANGE64_SLOTS - 1];
> +	void __rcu *slot[MAPLE_ARANGE64_SLOTS];
> +	unsigned long gap[MAPLE_ARANGE64_SLOTS];
> +	unsigned char meta;
> +};
> +
> +struct maple_alloc {
> +	unsigned long total;
> +	unsigned char node_count;
> +	unsigned int request_count;
> +	struct maple_alloc *slot[MAPLE_ALLOC_SLOTS];
> +};
> +
> +struct maple_topiary {
> +	struct maple_pnode *parent;
> +	struct maple_enode *next; /* Overlaps the pivot */
> +};
> +
> +enum maple_type {
> +	maple_dense,
> +	maple_leaf_64,
> +	maple_range_64,
> +	maple_arange_64,
> +};

> +struct maple_node {
> +	union {
> +		struct {
> +			struct maple_pnode *parent;
> +			void __rcu *slot[MAPLE_NODE_SLOTS];
> +		};
> +		struct {
> +			void *pad;
> +			struct rcu_head rcu;
> +			unsigned int ma_flags;
> +			enum maple_type type;
> +		};
> +		struct maple_range_64 mr64;
> +		struct maple_arange_64 ma64;
> +		struct maple_alloc alloc;
> +	};
> +};

This is somewhat inconsistent; would it make sense to have struct
maple_dense and struct maple_leaf_64, and maybe even struct maple_free,
such that one can write:

struct maple_node {
	union {
		/* maple_type: */
		struct maple_dense	md;
		struct maple_leaf_64	ml64;
		struct maple_range_64	mr64;
		struct maple_arange_64	ma64;

		/* internal, life-time: */
		struct maple_alloc	alloc;
		struct maple_free	free;
	};
};

Or something along those lines.