1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Block rq-qos policy for assigning an I/O priority class to requests.
4  *
5  * Using an rq-qos policy for assigning I/O priority class has two advantages
6  * over using the ioprio_set() system call:
7  *
8  * - This policy is cgroup based so it has all the advantages of cgroups.
9  * - While ioprio_set() does not affect page cache writeback I/O, this rq-qos
10  *   controller affects page cache writeback I/O for filesystems that support
11  *   assiociating a cgroup with writeback I/O. See also
12  *   Documentation/admin-guide/cgroup-v2.rst.
13  */
14 
15 #include <linux/blk-mq.h>
16 #include <linux/blk_types.h>
17 #include <linux/kernel.h>
18 #include <linux/module.h>
19 #include "blk-cgroup.h"
20 #include "blk-ioprio.h"
21 #include "blk-rq-qos.h"
22 
23 /**
24  * enum prio_policy - I/O priority class policy.
25  * @POLICY_NO_CHANGE: (default) do not modify the I/O priority class.
26  * @POLICY_NONE_TO_RT: modify IOPRIO_CLASS_NONE into IOPRIO_CLASS_RT.
27  * @POLICY_RESTRICT_TO_BE: modify IOPRIO_CLASS_NONE and IOPRIO_CLASS_RT into
28  *		IOPRIO_CLASS_BE.
29  * @POLICY_ALL_TO_IDLE: change the I/O priority class into IOPRIO_CLASS_IDLE.
30  *
31  * See also <linux/ioprio.h>.
32  */
33 enum prio_policy {
34 	POLICY_NO_CHANGE	= 0,
35 	POLICY_NONE_TO_RT	= 1,
36 	POLICY_RESTRICT_TO_BE	= 2,
37 	POLICY_ALL_TO_IDLE	= 3,
38 };
39 
40 static const char *policy_name[] = {
41 	[POLICY_NO_CHANGE]	= "no-change",
42 	[POLICY_NONE_TO_RT]	= "none-to-rt",
43 	[POLICY_RESTRICT_TO_BE]	= "restrict-to-be",
44 	[POLICY_ALL_TO_IDLE]	= "idle",
45 };
46 
47 static struct blkcg_policy ioprio_policy;
48 
49 /**
50  * struct ioprio_blkg - Per (cgroup, request queue) data.
51  * @pd: blkg_policy_data structure.
52  */
53 struct ioprio_blkg {
54 	struct blkg_policy_data pd;
55 };
56 
57 /**
58  * struct ioprio_blkcg - Per cgroup data.
59  * @cpd: blkcg_policy_data structure.
60  * @prio_policy: One of the IOPRIO_CLASS_* values. See also <linux/ioprio.h>.
61  */
62 struct ioprio_blkcg {
63 	struct blkcg_policy_data cpd;
64 	enum prio_policy	 prio_policy;
65 };
66 
pd_to_ioprio(struct blkg_policy_data * pd)67 static inline struct ioprio_blkg *pd_to_ioprio(struct blkg_policy_data *pd)
68 {
69 	return pd ? container_of(pd, struct ioprio_blkg, pd) : NULL;
70 }
71 
blkcg_to_ioprio_blkcg(struct blkcg * blkcg)72 static struct ioprio_blkcg *blkcg_to_ioprio_blkcg(struct blkcg *blkcg)
73 {
74 	return container_of(blkcg_to_cpd(blkcg, &ioprio_policy),
75 			    struct ioprio_blkcg, cpd);
76 }
77 
78 static struct ioprio_blkcg *
ioprio_blkcg_from_css(struct cgroup_subsys_state * css)79 ioprio_blkcg_from_css(struct cgroup_subsys_state *css)
80 {
81 	return blkcg_to_ioprio_blkcg(css_to_blkcg(css));
82 }
83 
ioprio_blkcg_from_bio(struct bio * bio)84 static struct ioprio_blkcg *ioprio_blkcg_from_bio(struct bio *bio)
85 {
86 	struct blkg_policy_data *pd = blkg_to_pd(bio->bi_blkg, &ioprio_policy);
87 
88 	if (!pd)
89 		return NULL;
90 
91 	return blkcg_to_ioprio_blkcg(pd->blkg->blkcg);
92 }
93 
ioprio_show_prio_policy(struct seq_file * sf,void * v)94 static int ioprio_show_prio_policy(struct seq_file *sf, void *v)
95 {
96 	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(seq_css(sf));
97 
98 	seq_printf(sf, "%s\n", policy_name[blkcg->prio_policy]);
99 	return 0;
100 }
101 
ioprio_set_prio_policy(struct kernfs_open_file * of,char * buf,size_t nbytes,loff_t off)102 static ssize_t ioprio_set_prio_policy(struct kernfs_open_file *of, char *buf,
103 				      size_t nbytes, loff_t off)
104 {
105 	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(of_css(of));
106 	int ret;
107 
108 	if (off != 0)
109 		return -EIO;
110 	/* kernfs_fop_write_iter() terminates 'buf' with '\0'. */
111 	ret = sysfs_match_string(policy_name, buf);
112 	if (ret < 0)
113 		return ret;
114 	blkcg->prio_policy = ret;
115 	return nbytes;
116 }
117 
118 static struct blkg_policy_data *
ioprio_alloc_pd(struct gendisk * disk,struct blkcg * blkcg,gfp_t gfp)119 ioprio_alloc_pd(struct gendisk *disk, struct blkcg *blkcg, gfp_t gfp)
120 {
121 	struct ioprio_blkg *ioprio_blkg;
122 
123 	ioprio_blkg = kzalloc(sizeof(*ioprio_blkg), gfp);
124 	if (!ioprio_blkg)
125 		return NULL;
126 
127 	return &ioprio_blkg->pd;
128 }
129 
ioprio_free_pd(struct blkg_policy_data * pd)130 static void ioprio_free_pd(struct blkg_policy_data *pd)
131 {
132 	struct ioprio_blkg *ioprio_blkg = pd_to_ioprio(pd);
133 
134 	kfree(ioprio_blkg);
135 }
136 
ioprio_alloc_cpd(gfp_t gfp)137 static struct blkcg_policy_data *ioprio_alloc_cpd(gfp_t gfp)
138 {
139 	struct ioprio_blkcg *blkcg;
140 
141 	blkcg = kzalloc(sizeof(*blkcg), gfp);
142 	if (!blkcg)
143 		return NULL;
144 	blkcg->prio_policy = POLICY_NO_CHANGE;
145 	return &blkcg->cpd;
146 }
147 
ioprio_free_cpd(struct blkcg_policy_data * cpd)148 static void ioprio_free_cpd(struct blkcg_policy_data *cpd)
149 {
150 	struct ioprio_blkcg *blkcg = container_of(cpd, typeof(*blkcg), cpd);
151 
152 	kfree(blkcg);
153 }
154 
155 #define IOPRIO_ATTRS						\
156 	{							\
157 		.name		= "prio.class",			\
158 		.seq_show	= ioprio_show_prio_policy,	\
159 		.write		= ioprio_set_prio_policy,	\
160 	},							\
161 	{ } /* sentinel */
162 
163 /* cgroup v2 attributes */
164 static struct cftype ioprio_files[] = {
165 	IOPRIO_ATTRS
166 };
167 
168 /* cgroup v1 attributes */
169 static struct cftype ioprio_legacy_files[] = {
170 	IOPRIO_ATTRS
171 };
172 
173 static struct blkcg_policy ioprio_policy = {
174 	.dfl_cftypes	= ioprio_files,
175 	.legacy_cftypes = ioprio_legacy_files,
176 
177 	.cpd_alloc_fn	= ioprio_alloc_cpd,
178 	.cpd_free_fn	= ioprio_free_cpd,
179 
180 	.pd_alloc_fn	= ioprio_alloc_pd,
181 	.pd_free_fn	= ioprio_free_pd,
182 };
183 
blkcg_set_ioprio(struct bio * bio)184 void blkcg_set_ioprio(struct bio *bio)
185 {
186 	struct ioprio_blkcg *blkcg = ioprio_blkcg_from_bio(bio);
187 	u16 prio;
188 
189 	if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
190 		return;
191 
192 	/*
193 	 * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
194 	 * correspond to a lower priority. Hence, the max_t() below selects
195 	 * the lower priority of bi_ioprio and the cgroup I/O priority class.
196 	 * If the bio I/O priority equals IOPRIO_CLASS_NONE, the cgroup I/O
197 	 * priority is assigned to the bio.
198 	 */
199 	prio = max_t(u16, bio->bi_ioprio,
200 			IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));
201 	if (prio > bio->bi_ioprio)
202 		bio->bi_ioprio = prio;
203 }
204 
blk_ioprio_exit(struct gendisk * disk)205 void blk_ioprio_exit(struct gendisk *disk)
206 {
207 	blkcg_deactivate_policy(disk, &ioprio_policy);
208 }
209 
blk_ioprio_init(struct gendisk * disk)210 int blk_ioprio_init(struct gendisk *disk)
211 {
212 	return blkcg_activate_policy(disk, &ioprio_policy);
213 }
214 
ioprio_init(void)215 static int __init ioprio_init(void)
216 {
217 	return blkcg_policy_register(&ioprio_policy);
218 }
219 
ioprio_exit(void)220 static void __exit ioprio_exit(void)
221 {
222 	blkcg_policy_unregister(&ioprio_policy);
223 }
224 
225 module_init(ioprio_init);
226 module_exit(ioprio_exit);
227