include/os/linux/spl/sys/shrinker.h

   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 #define spl_register_shrinker(x)        register_shrinker(x)
  68 #define spl_unregister_shrinker(x)      unregister_shrinker(x)
  69
  70 /*
  71  * Linux 3.0 to 3.11 Shrinker API Compatibility.
  72  */
  73 #if defined(HAVE_SINGLE_SHRINKER_CALLBACK)
  74 #define SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost)   \
  75 static int                                                              \
  76 __ ## varname ## _wrapper(struct shrinker *shrink, struct shrink_control *sc)\
  77 {                                                                       \
  78         if (sc->nr_to_scan != 0) {                                      \
  79                 (void) scanfunc(shrink, sc);                            \
  80         }                                                               \
  81         return (countfunc(shrink, sc));                                 \
  82 }                                                                       \
  83                                                                         \
  84 static struct shrinker varname = {                                      \
  85         .shrink = __ ## varname ## _wrapper,                            \
  86         .seeks = seek_cost,                                             \
  87 }
  88
  89 #define SHRINK_STOP     (-1)
  90
  91 /*
  92  * Linux 3.12 and later Shrinker API Compatibility.
  93  */
  94 #elif defined(HAVE_SPLIT_SHRINKER_CALLBACK)
  95 #define SPL_SHRINKER_DECLARE(varname, countfunc, scanfunc, seek_cost)   \
  96 static struct shrinker varname = {                                      \
  97         .count_objects = countfunc,                                     \
  98         .scan_objects = scanfunc,                                       \
  99         .seeks = seek_cost,                                             \
 100 }
 101
 102 #else
 103 /*
 104  * Linux 2.x to 2.6.22, or a newer shrinker API has been introduced.
 105  */
 106 #error "Unknown shrinker callback"
 107 #endif
 108
 109 #endif /* SPL_SHRINKER_H */