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

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Date:   Fri, 14 May 2021 12:56:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Liam Howlett <liam.howlett@...cle.com>
Cc:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Rik van Riel <riel@...riel.com>,
        Michel Lespinasse <walken.cr@...il.com>
Subject: Re: [PATCH 26/94] Maple Tree: Add new data structure


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.