include/linux/percpu_counter.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _LINUX_PERCPU_COUNTER_H
   3 #define _LINUX_PERCPU_COUNTER_H
   4 /*
   5  * A simple "approximate counter" for use in ext2 and ext3 superblocks.
   6  *
   7  * WARNING: these things are HUGE.  4 kbytes per counter on 32-way P4.
   8  */
   9
  10 #include <linux/spinlock.h>
  11 #include <linux/smp.h>
  12 #include <linux/list.h>
  13 #include <linux/threads.h>
  14 #include <linux/percpu.h>
  15 #include <linux/types.h>
  16
  17 /* percpu_counter batch for local add or sub */
  18 #define PERCPU_COUNTER_LOCAL_BATCH      INT_MAX
  19
  20 #ifdef CONFIG_SMP
  21
  22 struct percpu_counter {
  23         raw_spinlock_t lock;
  24         s64 count;
  25 #ifdef CONFIG_HOTPLUG_CPU
  26         struct list_head list;  /* All percpu_counters are on a list */
  27 #endif
  28         s32 __percpu *counters;
  29 };
  30
  31 extern int percpu_counter_batch;
  32
  33 int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
  34                           struct lock_class_key *key);
  35
  36 #define percpu_counter_init(fbc, value, gfp)                            \
  37         ({                                                              \
  38                 static struct lock_class_key __key;                     \
  39                                                                         \
  40                 __percpu_counter_init(fbc, value, gfp, &__key);         \
  41         })
  42
  43 void percpu_counter_destroy(struct percpu_counter *fbc);
  44 void percpu_counter_set(struct percpu_counter *fbc, s64 amount);
  45 void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount,
  46                               s32 batch);
  47 s64 __percpu_counter_sum(struct percpu_counter *fbc);
  48 int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch);
  49 void percpu_counter_sync(struct percpu_counter *fbc);
  50
  51 static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
  52 {
  53         return __percpu_counter_compare(fbc, rhs, percpu_counter_batch);
  54 }
  55
  56 static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
  57 {
  58         percpu_counter_add_batch(fbc, amount, percpu_counter_batch);
  59 }
  60
  61 /*
  62  * With percpu_counter_add_local() and percpu_counter_sub_local(), counts
  63  * are accumulated in local per cpu counter and not in fbc->count until
  64  * local count overflows PERCPU_COUNTER_LOCAL_BATCH. This makes counter
  65  * write efficient.
  66  * But percpu_counter_sum(), instead of percpu_counter_read(), needs to be
  67  * used to add up the counts from each CPU to account for all the local
  68  * counts. So percpu_counter_add_local() and percpu_counter_sub_local()
  69  * should be used when a counter is updated frequently and read rarely.
  70  */
  71 static inline void
  72 percpu_counter_add_local(struct percpu_counter *fbc, s64 amount)
  73 {
  74         percpu_counter_add_batch(fbc, amount, PERCPU_COUNTER_LOCAL_BATCH);
  75 }
  76
  77 static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
  78 {
  79         s64 ret = __percpu_counter_sum(fbc);
  80         return ret < 0 ? 0 : ret;
  81 }
  82
  83 static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
  84 {
  85         return __percpu_counter_sum(fbc);
  86 }
  87
  88 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
  89 {
  90         return fbc->count;
  91 }
  92
  93 /*
  94  * It is possible for the percpu_counter_read() to return a small negative
  95  * number for some counter which should never be negative.
  96  *
  97  */
  98 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
  99 {
 100         /* Prevent reloads of fbc->count */
 101         s64 ret = READ_ONCE(fbc->count);
 102
 103         if (ret >= 0)
 104                 return ret;
 105         return 0;
 106 }
 107
 108 static inline bool percpu_counter_initialized(struct percpu_counter *fbc)
 109 {
 110         return (fbc->counters != NULL);
 111 }
 112
 113 #else /* !CONFIG_SMP */
 114
 115 struct percpu_counter {
 116         s64 count;
 117 };
 118
 119 static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount,
 120                                       gfp_t gfp)
 121 {
 122         fbc->count = amount;
 123         return 0;
 124 }
 125
 126 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
 127 {
 128 }
 129
 130 static inline void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
 131 {
 132         fbc->count = amount;
 133 }
 134
 135 static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
 136 {
 137         if (fbc->count > rhs)
 138                 return 1;
 139         else if (fbc->count < rhs)
 140                 return -1;
 141         else
 142                 return 0;
 143 }
 144
 145 static inline int
 146 __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
 147 {
 148         return percpu_counter_compare(fbc, rhs);
 149 }
 150
 151 static inline void
 152 percpu_counter_add(struct percpu_counter *fbc, s64 amount)
 153 {
 154         preempt_disable();
 155         fbc->count += amount;
 156         preempt_enable();
 157 }
 158
 159 /* non-SMP percpu_counter_add_local is the same with percpu_counter_add */
 160 static inline void
 161 percpu_counter_add_local(struct percpu_counter *fbc, s64 amount)
 162 {
 163         percpu_counter_add(fbc, amount);
 164 }
 165
 166 static inline void
 167 percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch)
 168 {
 169         percpu_counter_add(fbc, amount);
 170 }
 171
 172 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
 173 {
 174         return fbc->count;
 175 }
 176
 177 /*
 178  * percpu_counter is intended to track positive numbers. In the UP case the
 179  * number should never be negative.
 180  */
 181 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
 182 {
 183         return fbc->count;
 184 }
 185
 186 static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
 187 {
 188         return percpu_counter_read_positive(fbc);
 189 }
 190
 191 static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
 192 {
 193         return percpu_counter_read(fbc);
 194 }
 195
 196 static inline bool percpu_counter_initialized(struct percpu_counter *fbc)
 197 {
 198         return true;
 199 }
 200
 201 static inline void percpu_counter_sync(struct percpu_counter *fbc)
 202 {
 203 }
 204 #endif  /* CONFIG_SMP */
 205
 206 static inline void percpu_counter_inc(struct percpu_counter *fbc)
 207 {
 208         percpu_counter_add(fbc, 1);
 209 }
 210
 211 static inline void percpu_counter_dec(struct percpu_counter *fbc)
 212 {
 213         percpu_counter_add(fbc, -1);
 214 }
 215
 216 static inline void percpu_counter_sub(struct percpu_counter *fbc, s64 amount)
 217 {
 218         percpu_counter_add(fbc, -amount);
 219 }
 220
 221 static inline void
 222 percpu_counter_sub_local(struct percpu_counter *fbc, s64 amount)
 223 {
 224         percpu_counter_add_local(fbc, -amount);
 225 }
 226
 227 #endif /* _LINUX_PERCPU_COUNTER_H */