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); 263