1 /*
2  *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
3  *  Copyright (C) 2007 The Regents of the University of California.
4  *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
5  *  Written by Brian Behlendorf <behlendorf1@llnl.gov>.
6  *  UCRL-CODE-235197
7  *
8  *  This file is part of the SPL, Solaris Porting Layer.
9  *
10  *  The SPL is free software; you can redistribute it and/or modify it
11  *  under the terms of the GNU General Public License as published by the
12  *  Free Software Foundation; either version 2 of the License, or (at your
13  *  option) any later version.
14  *
15  *  The SPL is distributed in the hope that it will be useful, but WITHOUT
16  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
17  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
18  *  for more details.
19  *
20  *  You should have received a copy of the GNU General Public License along
21  *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
22  */
23 
24 #ifndef _SPL_SHRINKER_H
25 #define	_SPL_SHRINKER_H
26 
27 #include <linux/mm.h>
28 #include <linux/fs.h>
29 
30 /*
31  * Due to frequent changes in the shrinker API the following
32  * compatibility wrappers should be used.  They are as follows:
33  *
34  *   SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost);
35  *
36  * SPL_SHRINKER_DECLARE is used to declare a shrinker with the name varname,
37  * which is passed to spl_register_shrinker()/spl_unregister_shrinker().
38  * The countfunc returns the number of free-able objects.
39  * The scanfunc returns the number of objects that were freed.
40  * The callbacks can return SHRINK_STOP if further calls can't make any more
41  * progress.  Note that a return value of SHRINK_EMPTY is currently not
42  * supported.
43  *
44  * Example:
45  *
46  * static unsigned long
47  * my_count(struct shrinker *shrink, struct shrink_control *sc)
48  * {
49  *	...calculate number of objects in the cache...
50  *
51  *	return (number of objects in the cache);
52  * }
53  *
54  * static unsigned long
55  * my_scan(struct shrinker *shrink, struct shrink_control *sc)
56  * {
57  *	...scan objects in the cache and reclaim them...
58  * }
59  *
60  * SPL_SHRINKER_DECLARE(my_shrinker, my_count, my_scan, DEFAULT_SEEKS);
61  *
62  * void my_init_func(void) {
63  *	spl_register_shrinker(&my_shrinker);
64  * }
65  */
66 
67 #ifdef HAVE_REGISTER_SHRINKER_VARARG
68 #define	spl_register_shrinker(x)	register_shrinker(x, "zfs-arc-shrinker")
69 #else
70 #define	spl_register_shrinker(x)	register_shrinker(x)
71 #endif
72 #define	spl_unregister_shrinker(x)	unregister_shrinker(x)
73 
74 /*
75  * Linux 3.0 to 3.11 Shrinker API Compatibility.
76  */
77 #if defined(HAVE_SINGLE_SHRINKER_CALLBACK)
78 #define	SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost)	\
79 static int								\
80 __ ## varname ## _wrapper(struct shrinker *shrink, struct shrink_control *sc)\
81 {									\
82 	if (sc->nr_to_scan != 0) {					\
83 		(void) scanfunc(shrink, sc);				\
84 	}								\
85 	return (countfunc(shrink, sc));					\
86 }									\
87 									\
88 static struct shrinker varname = {					\
89 	.shrink = __ ## varname ## _wrapper,				\
90 	.seeks = seek_cost,						\
91 }
92 
93 #define	SHRINK_STOP	(-1)
94 
95 /*
96  * Linux 3.12 and later Shrinker API Compatibility.
97  */
98 #elif defined(HAVE_SPLIT_SHRINKER_CALLBACK)
99 #define	SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost)	\
100 static struct shrinker varname = {					\
101 	.count_objects = countfunc,					\
102 	.scan_objects = scanfunc,					\
103 	.seeks = seek_cost,						\
104 }
105 
106 #else
107 /*
108  * Linux 2.x to 2.6.22, or a newer shrinker API has been introduced.
109  */
110 #error "Unknown shrinker callback"
111 #endif
112 
113 #endif /* SPL_SHRINKER_H */
114