1 /*-
2  * Copyright (c) 2020 Emmanuel Vadot <manu@FreeBSD.org>
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions
6  * are met:
7  * 1. Redistributions of source code must retain the above copyright
8  *    notice, this list of conditions and the following disclaimer.
9  * 2. Redistributions in binary form must reproduce the above copyright
10  *    notice, this list of conditions and the following disclaimer in the
11  *    documentation and/or other materials provided with the distribution.
12  *
13  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16  * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
23  * SUCH DAMAGE.
24  *
25  * $FreeBSD$
26  */
27 
28 
29 #include <sys/cdefs.h>
30 __FBSDID("$FreeBSD$");
31 
32 #include <sys/param.h>
33 #include <sys/systm.h>
34 #include <sys/kernel.h>
35 #include <sys/queue.h>
36 #include <sys/eventhandler.h>
37 #include <sys/sx.h>
38 
39 #include <linux/compat.h>
40 #include <linux/shrinker.h>
41 
42 TAILQ_HEAD(, shrinker) lkpi_shrinkers = TAILQ_HEAD_INITIALIZER(lkpi_shrinkers);
43 static struct sx sx_shrinker;
44 
45 int
46 linuxkpi_register_shrinker(struct shrinker *s)
47 {
48 
49 	KASSERT(s != NULL, ("NULL shrinker"));
50 	KASSERT(s->count_objects != NULL, ("NULL shrinker"));
51 	KASSERT(s->scan_objects != NULL, ("NULL shrinker"));
52 	sx_xlock(&sx_shrinker);
53 	TAILQ_INSERT_TAIL(&lkpi_shrinkers, s, next);
54 	sx_xunlock(&sx_shrinker);
55 	return (0);
56 }
57 
58 void
59 linuxkpi_unregister_shrinker(struct shrinker *s)
60 {
61 
62 	sx_xlock(&sx_shrinker);
63 	TAILQ_REMOVE(&lkpi_shrinkers, s, next);
64 	sx_xunlock(&sx_shrinker);
65 }
66 
67 #define	SHRINKER_BATCH	512
68 
69 static void
70 shrinker_shrink(struct shrinker *s)
71 {
72 	struct shrink_control sc;
73 	unsigned long can_free;
74 	unsigned long batch;
75 	unsigned long scanned = 0;
76 	unsigned long ret;
77 
78 	can_free = s->count_objects(s, &sc);
79 	if (can_free <= 0)
80 		return;
81 
82 	batch = s->batch ? s->batch : SHRINKER_BATCH;
83 	while (scanned <= can_free) {
84 		sc.nr_to_scan = batch;
85 		ret = s->scan_objects(s, &sc);
86 		if (ret == SHRINK_STOP)
87 			break;
88 		scanned += batch;
89 	}
90 }
91 
92 static void
93 linuxkpi_vm_lowmem(void *arg __unused)
94 {
95 	struct shrinker *s;
96 
97 	sx_xlock(&sx_shrinker);
98 	TAILQ_FOREACH(s, &lkpi_shrinkers, next) {
99 		shrinker_shrink(s);
100 	}
101 	sx_xunlock(&sx_shrinker);
102 }
103 
104 static eventhandler_tag lowmem_tag;
105 
106 static void
107 linuxkpi_sysinit_shrinker(void *arg __unused)
108 {
109 
110 	sx_init(&sx_shrinker, "lkpi-shrinker");
111 	lowmem_tag = EVENTHANDLER_REGISTER(vm_lowmem, linuxkpi_vm_lowmem,
112 	    NULL, EVENTHANDLER_PRI_FIRST);
113 }
114 
115 static void
116 linuxkpi_sysuninit_shrinker(void *arg __unused)
117 {
118 
119 	sx_destroy(&sx_shrinker);
120 	EVENTHANDLER_DEREGISTER(vm_lowmem, lowmem_tag);
121 }
122 
123 SYSINIT(linuxkpi_shrinker, SI_SUB_DRIVERS, SI_ORDER_ANY,
124     linuxkpi_sysinit_shrinker, NULL);
125 SYSUNINIT(linuxkpi_shrinker, SI_SUB_DRIVERS, SI_ORDER_ANY,
126     linuxkpi_sysuninit_shrinker, NULL);
127