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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-cgroup.h> | |
16 | #include <linux/blk-mq.h> | |
17 | #include <linux/blk_types.h> | |
18 | #include <linux/kernel.h> | |
19 | #include <linux/module.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 | ||
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 | ||
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 * | |
79 | ioprio_blkcg_from_css(struct cgroup_subsys_state *css) | |
80 | { | |
81 | return blkcg_to_ioprio_blkcg(css_to_blkcg(css)); | |
82 | } | |
83 | ||
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 | ||
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 | ||
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 | ||
116 | return nbytes; | |
117 | } | |
118 | ||
119 | static struct blkg_policy_data * | |
120 | ioprio_alloc_pd(gfp_t gfp, struct request_queue *q, struct blkcg *blkcg) | |
121 | { | |
122 | struct ioprio_blkg *ioprio_blkg; | |
123 | ||
124 | ioprio_blkg = kzalloc(sizeof(*ioprio_blkg), gfp); | |
125 | if (!ioprio_blkg) | |
126 | return NULL; | |
127 | ||
128 | return &ioprio_blkg->pd; | |
129 | } | |
130 | ||
131 | static void ioprio_free_pd(struct blkg_policy_data *pd) | |
132 | { | |
133 | struct ioprio_blkg *ioprio_blkg = pd_to_ioprio(pd); | |
134 | ||
135 | kfree(ioprio_blkg); | |
136 | } | |
137 | ||
138 | static struct blkcg_policy_data *ioprio_alloc_cpd(gfp_t gfp) | |
139 | { | |
140 | struct ioprio_blkcg *blkcg; | |
141 | ||
142 | blkcg = kzalloc(sizeof(*blkcg), gfp); | |
143 | if (!blkcg) | |
144 | return NULL; | |
145 | blkcg->prio_policy = POLICY_NO_CHANGE; | |
146 | return &blkcg->cpd; | |
147 | } | |
148 | ||
149 | static void ioprio_free_cpd(struct blkcg_policy_data *cpd) | |
150 | { | |
151 | struct ioprio_blkcg *blkcg = container_of(cpd, typeof(*blkcg), cpd); | |
152 | ||
153 | kfree(blkcg); | |
154 | } | |
155 | ||
156 | #define IOPRIO_ATTRS \ | |
157 | { \ | |
158 | .name = "prio.class", \ | |
159 | .seq_show = ioprio_show_prio_policy, \ | |
160 | .write = ioprio_set_prio_policy, \ | |
161 | }, \ | |
162 | { } /* sentinel */ | |
163 | ||
164 | /* cgroup v2 attributes */ | |
165 | static struct cftype ioprio_files[] = { | |
166 | IOPRIO_ATTRS | |
167 | }; | |
168 | ||
169 | /* cgroup v1 attributes */ | |
170 | static struct cftype ioprio_legacy_files[] = { | |
171 | IOPRIO_ATTRS | |
172 | }; | |
173 | ||
174 | static struct blkcg_policy ioprio_policy = { | |
175 | .dfl_cftypes = ioprio_files, | |
176 | .legacy_cftypes = ioprio_legacy_files, | |
177 | ||
178 | .cpd_alloc_fn = ioprio_alloc_cpd, | |
179 | .cpd_free_fn = ioprio_free_cpd, | |
180 | ||
181 | .pd_alloc_fn = ioprio_alloc_pd, | |
182 | .pd_free_fn = ioprio_free_pd, | |
183 | }; | |
184 | ||
185 | struct blk_ioprio { | |
186 | struct rq_qos rqos; | |
187 | }; | |
188 | ||
189 | static void blkcg_ioprio_track(struct rq_qos *rqos, struct request *rq, | |
190 | struct bio *bio) | |
191 | { | |
192 | struct ioprio_blkcg *blkcg = ioprio_blkcg_from_bio(bio); | |
193 | ||
194 | /* | |
195 | * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers | |
196 | * correspond to a lower priority. Hence, the max_t() below selects | |
197 | * the lower priority of bi_ioprio and the cgroup I/O priority class. | |
198 | * If the cgroup policy has been set to POLICY_NO_CHANGE == 0, the | |
199 | * bio I/O priority is not modified. If the bio I/O priority equals | |
200 | * IOPRIO_CLASS_NONE, the cgroup I/O priority is assigned to the bio. | |
201 | */ | |
202 | bio->bi_ioprio = max_t(u16, bio->bi_ioprio, | |
203 | IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0)); | |
204 | } | |
205 | ||
206 | static void blkcg_ioprio_exit(struct rq_qos *rqos) | |
207 | { | |
208 | struct blk_ioprio *blkioprio_blkg = | |
209 | container_of(rqos, typeof(*blkioprio_blkg), rqos); | |
210 | ||
211 | blkcg_deactivate_policy(rqos->q, &ioprio_policy); | |
212 | kfree(blkioprio_blkg); | |
213 | } | |
214 | ||
215 | static struct rq_qos_ops blkcg_ioprio_ops = { | |
216 | .track = blkcg_ioprio_track, | |
217 | .exit = blkcg_ioprio_exit, | |
218 | }; | |
219 | ||
220 | int blk_ioprio_init(struct request_queue *q) | |
221 | { | |
222 | struct blk_ioprio *blkioprio_blkg; | |
223 | struct rq_qos *rqos; | |
224 | int ret; | |
225 | ||
226 | blkioprio_blkg = kzalloc(sizeof(*blkioprio_blkg), GFP_KERNEL); | |
227 | if (!blkioprio_blkg) | |
228 | return -ENOMEM; | |
229 | ||
230 | ret = blkcg_activate_policy(q, &ioprio_policy); | |
231 | if (ret) { | |
232 | kfree(blkioprio_blkg); | |
233 | return ret; | |
234 | } | |
235 | ||
236 | rqos = &blkioprio_blkg->rqos; | |
237 | rqos->id = RQ_QOS_IOPRIO; | |
238 | rqos->ops = &blkcg_ioprio_ops; | |
239 | rqos->q = q; | |
240 | ||
241 | /* | |
242 | * Registering the rq-qos policy after activating the blk-cgroup | |
243 | * policy guarantees that ioprio_blkcg_from_bio(bio) != NULL in the | |
244 | * rq-qos callbacks. | |
245 | */ | |
246 | rq_qos_add(q, rqos); | |
247 | ||
248 | return 0; | |
249 | } | |
250 | ||
251 | static int __init ioprio_init(void) | |
252 | { | |
253 | return blkcg_policy_register(&ioprio_policy); | |
254 | } | |
255 | ||
256 | static void __exit ioprio_exit(void) | |
257 | { | |
258 | blkcg_policy_unregister(&ioprio_policy); | |
259 | } | |
260 | ||
261 | module_init(ioprio_init); | |
262 | module_exit(ioprio_exit); |