block/blk-ioprio.c

   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);