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 */
34enum 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
42static 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
50static struct blkcg_policy ioprio_policy;
51
52/**
53 * struct ioprio_blkg - Per (cgroup, request queue) data.
54 * @pd: blkg_policy_data structure.
55 */
56struct 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 */
65struct ioprio_blkcg {
66	struct blkcg_policy_data cpd;
67	enum prio_policy	 prio_policy;
68};
69
70static 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
75static 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
81static struct ioprio_blkcg *
82ioprio_blkcg_from_css(struct cgroup_subsys_state *css)
83{
84	return blkcg_to_ioprio_blkcg(css_to_blkcg(css));
85}
86
87static 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
97static 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
105static 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
121static struct blkg_policy_data *
122ioprio_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
133static 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
140static 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
151static 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 */
167static struct cftype ioprio_files[] = {
168	IOPRIO_ATTRS
169};
170
171/* cgroup v1 attributes */
172static struct cftype ioprio_legacy_files[] = {
173	IOPRIO_ATTRS
174};
175
176static 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
187void 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
222void blk_ioprio_exit(struct gendisk *disk)
223{
224	blkcg_deactivate_policy(disk, &ioprio_policy);
225}
226
227int blk_ioprio_init(struct gendisk *disk)
228{
229	return blkcg_activate_policy(disk, &ioprio_policy);
230}
231
232static int __init ioprio_init(void)
233{
234	return blkcg_policy_register(&ioprio_policy);
235}
236
237static void __exit ioprio_exit(void)
238{
239	blkcg_policy_unregister(&ioprio_policy);
240}
241
242module_init(ioprio_init);
243module_exit(ioprio_exit);
244