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-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_PROMOTE_TO_RT: modify no-IOPRIO_CLASS_RT to 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  * @POLICY_NONE_TO_RT: an alias for POLICY_PROMOTE_TO_RT.
  31  *
  32  * See also <linux/ioprio.h>.
  33  */
  34 enum prio_policy {
  35         POLICY_NO_CHANGE        = 0,
  36         POLICY_PROMOTE_TO_RT    = 1,
  37         POLICY_RESTRICT_TO_BE   = 2,
  38         POLICY_ALL_TO_IDLE      = 3,
  39         POLICY_NONE_TO_RT       = 4,
  40 };
  41
  42 static const char *policy_name[] = {
  43         [POLICY_NO_CHANGE]      = "no-change",
  44         [POLICY_PROMOTE_TO_RT]  = "promote-to-rt",
  45         [POLICY_RESTRICT_TO_BE] = "restrict-to-be",
  46         [POLICY_ALL_TO_IDLE]    = "idle",
  47         [POLICY_NONE_TO_RT]     = "none-to-rt",
  48 };
  49
  50 static struct blkcg_policy ioprio_policy;
  51
  52 /**
  53  * struct ioprio_blkg - Per (cgroup, request queue) data.
  54  * @pd: blkg_policy_data structure.
  55  */
  56 struct ioprio_blkg {
  57         struct blkg_policy_data pd;
  58 };
  59
  60 /**
  61  * struct ioprio_blkcg - Per cgroup data.
  62  * @cpd: blkcg_policy_data structure.
  63  * @prio_policy: One of the IOPRIO_CLASS_* values. See also <linux/ioprio.h>.
  64  */
  65 struct ioprio_blkcg {
  66         struct blkcg_policy_data cpd;
  67         enum prio_policy         prio_policy;
  68 };
  69
  70 static inline struct ioprio_blkg *pd_to_ioprio(struct blkg_policy_data *pd)
  71 {
  72         return pd ? container_of(pd, struct ioprio_blkg, pd) : NULL;
  73 }
  74
  75 static struct ioprio_blkcg *blkcg_to_ioprio_blkcg(struct blkcg *blkcg)
  76 {
  77         return container_of(blkcg_to_cpd(blkcg, &ioprio_policy),
  78                             struct ioprio_blkcg, cpd);
  79 }
  80
  81 static struct ioprio_blkcg *
  82 ioprio_blkcg_from_css(struct cgroup_subsys_state *css)
  83 {
  84         return blkcg_to_ioprio_blkcg(css_to_blkcg(css));
  85 }
  86
  87 static struct ioprio_blkcg *ioprio_blkcg_from_bio(struct bio *bio)
  88 {
  89         struct blkg_policy_data *pd = blkg_to_pd(bio->bi_blkg, &ioprio_policy);
  90
  91         if (!pd)
  92                 return NULL;
  93
  94         return blkcg_to_ioprio_blkcg(pd->blkg->blkcg);
  95 }
  96
  97 static int ioprio_show_prio_policy(struct seq_file *sf, void *v)
  98 {
  99         struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(seq_css(sf));
 100
 101         seq_printf(sf, "%s\n", policy_name[blkcg->prio_policy]);
 102         return 0;
 103 }
 104
 105 static ssize_t ioprio_set_prio_policy(struct kernfs_open_file *of, char *buf,
 106                                       size_t nbytes, loff_t off)
 107 {
 108         struct ioprio_blkcg *blkcg = ioprio_blkcg_from_css(of_css(of));
 109         int ret;
 110
 111         if (off != 0)
 112                 return -EIO;
 113         /* kernfs_fop_write_iter() terminates 'buf' with '\0'. */
 114         ret = sysfs_match_string(policy_name, buf);
 115         if (ret < 0)
 116                 return ret;
 117         blkcg->prio_policy = ret;
 118         return nbytes;
 119 }
 120
 121 static struct blkg_policy_data *
 122 ioprio_alloc_pd(struct gendisk *disk, struct blkcg *blkcg, gfp_t gfp)
 123 {
 124         struct ioprio_blkg *ioprio_blkg;
 125
 126         ioprio_blkg = kzalloc(sizeof(*ioprio_blkg), gfp);
 127         if (!ioprio_blkg)
 128                 return NULL;
 129
 130         return &ioprio_blkg->pd;
 131 }
 132
 133 static void ioprio_free_pd(struct blkg_policy_data *pd)
 134 {
 135         struct ioprio_blkg *ioprio_blkg = pd_to_ioprio(pd);
 136
 137         kfree(ioprio_blkg);
 138 }
 139
 140 static struct blkcg_policy_data *ioprio_alloc_cpd(gfp_t gfp)
 141 {
 142         struct ioprio_blkcg *blkcg;
 143
 144         blkcg = kzalloc(sizeof(*blkcg), gfp);
 145         if (!blkcg)
 146                 return NULL;
 147         blkcg->prio_policy = POLICY_NO_CHANGE;
 148         return &blkcg->cpd;
 149 }
 150
 151 static void ioprio_free_cpd(struct blkcg_policy_data *cpd)
 152 {
 153         struct ioprio_blkcg *blkcg = container_of(cpd, typeof(*blkcg), cpd);
 154
 155         kfree(blkcg);
 156 }
 157
 158 #define IOPRIO_ATTRS                                            \
 159         {                                                       \
 160                 .name           = "prio.class",                 \
 161                 .seq_show       = ioprio_show_prio_policy,      \
 162                 .write          = ioprio_set_prio_policy,       \
 163         },                                                      \
 164         { } /* sentinel */
 165
 166 /* cgroup v2 attributes */
 167 static struct cftype ioprio_files[] = {
 168         IOPRIO_ATTRS
 169 };
 170
 171 /* cgroup v1 attributes */
 172 static struct cftype ioprio_legacy_files[] = {
 173         IOPRIO_ATTRS
 174 };
 175
 176 static struct blkcg_policy ioprio_policy = {
 177         .dfl_cftypes    = ioprio_files,
 178         .legacy_cftypes = ioprio_legacy_files,
 179
 180         .cpd_alloc_fn   = ioprio_alloc_cpd,
 181         .cpd_free_fn    = ioprio_free_cpd,
 182
 183         .pd_alloc_fn    = ioprio_alloc_pd,
 184         .pd_free_fn     = ioprio_free_pd,
 185 };
 186
 187 void blkcg_set_ioprio(struct bio *bio)
 188 {
 189         struct ioprio_blkcg *blkcg = ioprio_blkcg_from_bio(bio);
 190         u16 prio;
 191
 192         if (!blkcg || blkcg->prio_policy == POLICY_NO_CHANGE)
 193                 return;
 194
 195         if (blkcg->prio_policy == POLICY_PROMOTE_TO_RT ||
 196             blkcg->prio_policy == POLICY_NONE_TO_RT) {
 197                 /*
 198                  * For RT threads, the default priority level is 4 because
 199                  * task_nice is 0. By promoting non-RT io-priority to RT-class
 200                  * and default level 4, those requests that are already
 201                  * RT-class but need a higher io-priority can use ioprio_set()
 202                  * to achieve this.
 203                  */
 204                 if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) != IOPRIO_CLASS_RT)
 205                         bio->bi_ioprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_RT, 4);
 206                 return;
 207         }
 208
 209         /*
 210          * Except for IOPRIO_CLASS_NONE, higher I/O priority numbers
 211          * correspond to a lower priority. Hence, the max_t() below selects
 212          * the lower priority of bi_ioprio and the cgroup I/O priority class.
 213          * If the bio I/O priority equals IOPRIO_CLASS_NONE, the cgroup I/O
 214          * priority is assigned to the bio.
 215          */
 216         prio = max_t(u16, bio->bi_ioprio,
 217                         IOPRIO_PRIO_VALUE(blkcg->prio_policy, 0));
 218         if (prio > bio->bi_ioprio)
 219                 bio->bi_ioprio = prio;
 220 }
 221
 222 void blk_ioprio_exit(struct gendisk *disk)
 223 {
 224         blkcg_deactivate_policy(disk, &ioprio_policy);
 225 }
 226
 227 int blk_ioprio_init(struct gendisk *disk)
 228 {
 229         return blkcg_activate_policy(disk, &ioprio_policy);
 230 }
 231
 232 static int __init ioprio_init(void)
 233 {
 234         return blkcg_policy_register(&ioprio_policy);
 235 }
 236
 237 static void __exit ioprio_exit(void)
 238 {
 239         blkcg_policy_unregister(&ioprio_policy);
 240 }
 241
 242 module_init(ioprio_init);
 243 module_exit(ioprio_exit);