linux-kernel - Re: [PATCH v4 v4 1/2] Union-Find: add a new module in kernel library

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Message-ID: <b511173c-53fe-4a93-8030-d99ed1b65bd6@redhat.com>
Date: Thu, 20 Jun 2024 10:54:46 -0400
From: Waiman Long <longman@...hat.com>
To: Xavier <xavier_qy@....com>, mkoutny@...e.com
Cc: lizefan.x@...edance.com, tj@...nel.org, hannes@...xchg.org,
 cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 v4 1/2] Union-Find: add a new module in kernel library

On 6/20/24 04:52, Xavier wrote:
> This patch implements a union-find data structure in the kernel library,
> which includes operations for allocating nodes, freeing nodes,
> finding the root of a node, and merging two nodes.
>
> Signed-off-by: Xavier <xavier_qy@....com>
> ---
>   MAINTAINERS                |  7 +++++++
>   include/linux/union_find.h | 30 ++++++++++++++++++++++++++++++
>   lib/Makefile               |  2 +-
>   lib/union_find.c           | 38 ++++++++++++++++++++++++++++++++++++++
>   4 files changed, 76 insertions(+), 1 deletion(-)
>   create mode 100644 include/linux/union_find.h
>   create mode 100644 lib/union_find.c
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index d6c90161c7..602d8c6f42 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -23054,6 +23054,13 @@ F:	drivers/cdrom/cdrom.c
>   F:	include/linux/cdrom.h
>   F:	include/uapi/linux/cdrom.h
>   
> +UNION-FIND
> +M:	Xavier <xavier_qy@....com>
> +L:	linux-kernel@...r.kernel.org
> +S:	Maintained
> +F:	include/linux/union_find.h
> +F:	lib/union_find.c
> +
>   UNIVERSAL FLASH STORAGE HOST CONTROLLER DRIVER
>   R:	Alim Akhtar <alim.akhtar@...sung.com>
>   R:	Avri Altman <avri.altman@....com>
> diff --git a/include/linux/union_find.h b/include/linux/union_find.h
> new file mode 100644
> index 0000000000..67e9f62bb3
> --- /dev/null
> +++ b/include/linux/union_find.h
> @@ -0,0 +1,30 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __LINUX_UNION_FIND_H
> +#define __LINUX_UNION_FIND_H
> +#include <linux/slab.h>
> +
> +/* Define a union-find node struct */
> +struct uf_node {
> +	struct uf_node *parent;
> +	unsigned int rank;
> +};
> +
> +/* Allocate nodes and initialize to 0 */
> +static inline struct uf_node *uf_nodes_alloc(unsigned int node_num)
> +{
> +	return kzalloc(sizeof(struct uf_node) * node_num, GFP_KERNEL);
> +}
> +
> +/* Free nodes*/
> +static inline void uf_nodes_free(struct uf_node *nodes)
> +{
> +	kfree(nodes);
> +}
> +
> +/* find the root of a node*/
> +struct uf_node *uf_find(struct uf_node *node);
> +
> +/* Merge two intersecting nodes */
> +void uf_union(struct uf_node *node1, struct uf_node *node2);
> +
> +#endif /*__LINUX_UNION_FIND_H*/
> diff --git a/lib/Makefile b/lib/Makefile
> index 3b17690456..e1769e6f03 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -34,7 +34,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
>   	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
>   	 earlycpio.o seq_buf.o siphash.o dec_and_lock.o \
>   	 nmi_backtrace.o win_minmax.o memcat_p.o \
> -	 buildid.o objpool.o
> +	 buildid.o objpool.o union_find.o
>   
>   lib-$(CONFIG_PRINTK) += dump_stack.o
>   lib-$(CONFIG_SMP) += cpumask.o
> diff --git a/lib/union_find.c b/lib/union_find.c
> new file mode 100644
> index 0000000000..2f77bae1ca
> --- /dev/null
> +++ b/lib/union_find.c
> @@ -0,0 +1,38 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/union_find.h>

I would suggest that you briefly document what is a union-find algorithm 
and data structure and what is it good for.

Cheers,
Longman

> +
> +struct uf_node *uf_find(struct uf_node *node)
> +{
> +	struct uf_node *parent;
> +
> +	if (!node->parent) {
> +		node->parent = node;
> +		return node;
> +	}
> +
> +	/*Find the root node and perform path compression at the same time*/
> +	while (node->parent != node) {
> +		parent = node->parent;
> +		node->parent = parent->parent;
> +		node = parent;
> +	}
> +	return node;
> +}
> +
> +/*Function to merge two sets, using union by rank*/
> +void uf_union(struct uf_node *node1, struct uf_node *node2)
> +{
> +	struct uf_node *root1 = uf_find(node1);
> +	struct uf_node *root2 = uf_find(node2);
> +
> +	if (root1 != root2) {
> +		if (root1->rank < root2->rank) {
> +			root1->parent = root2;
> +		} else if (root1->rank > root2->rank) {
> +			root2->parent = root1;
> +		} else {
> +			root2->parent = root1;
> +			root1->rank++;
> +		}
> +	}
> +}