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      1 #ifndef _LINUX_PERCPU_COUNTER_H
      2 #define _LINUX_PERCPU_COUNTER_H
      3 /*
      4  * A simple "approximate counter" for use in ext2 and ext3 superblocks.
      5  *
      6  * WARNING: these things are HUGE.  4 kbytes per counter on 32-way P4.
      7  */
      8 
      9 #include <linux/spinlock.h>
     10 #include <linux/smp.h>
     11 #include <linux/threads.h>
     12 #include <linux/percpu.h>
     13 #include <linux/types.h>
     14 
     15 #ifdef CONFIG_SMP
     16 
     17 struct percpu_counter {
     18 	spinlock_t lock;
     19 	s64 count;
     20 	s32 *counters;
     21 };
     22 
     23 #if NR_CPUS >= 16
     24 #define FBC_BATCH	(NR_CPUS*2)
     25 #else
     26 #define FBC_BATCH	(NR_CPUS*4)
     27 #endif
     28 
     29 static inline void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
     30 {
     31 	spin_lock_init(&fbc->lock);
     32 	fbc->count = amount;
     33 	fbc->counters = alloc_percpu(s32);
     34 }
     35 
     36 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
     37 {
     38 	free_percpu(fbc->counters);
     39 }
     40 
     41 void percpu_counter_mod(struct percpu_counter *fbc, s32 amount);
     42 s64 percpu_counter_sum(struct percpu_counter *fbc);
     43 
     44 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
     45 {
     46 	return fbc->count;
     47 }
     48 
     49 /*
     50  * It is possible for the percpu_counter_read() to return a small negative
     51  * number for some counter which should never be negative.
     52  *
     53  */
     54 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
     55 {
     56 	s64 ret = fbc->count;
     57 
     58 	barrier();		/* Prevent reloads of fbc->count */
     59 	if (ret >= 0)
     60 		return ret;
     61 	return 1;
     62 }
     63 
     64 #else
     65 
     66 struct percpu_counter {
     67 	s64 count;
     68 };
     69 
     70 static inline void percpu_counter_init(struct percpu_counter *fbc, s64 amount)
     71 {
     72 	fbc->count = amount;
     73 }
     74 
     75 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
     76 {
     77 }
     78 
     79 static inline void
     80 percpu_counter_mod(struct percpu_counter *fbc, s32 amount)
     81 {
     82 	preempt_disable();
     83 	fbc->count += amount;
     84 	preempt_enable();
     85 }
     86 
     87 static inline s64 percpu_counter_read(struct percpu_counter *fbc)
     88 {
     89 	return fbc->count;
     90 }
     91 
     92 static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
     93 {
     94 	return fbc->count;
     95 }
     96 
     97 static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
     98 {
     99 	return percpu_counter_read_positive(fbc);
    100 }
    101 
    102 #endif	/* CONFIG_SMP */
    103 
    104 static inline void percpu_counter_inc(struct percpu_counter *fbc)
    105 {
    106 	percpu_counter_mod(fbc, 1);
    107 }
    108 
    109 static inline void percpu_counter_dec(struct percpu_counter *fbc)
    110 {
    111 	percpu_counter_mod(fbc, -1);
    112 }
    113 
    114 #endif /* _LINUX_PERCPU_COUNTER_H */
    115