xref: /linux-6.15/include/linux/percpu_counter.h (revision 4bedea94) 
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/config.h>
10 #include <linux/spinlock.h>
11 #include <linux/smp.h>
12 #include <linux/threads.h>
13 #include <linux/percpu.h>
14 
15 #ifdef CONFIG_SMP
16 
17 struct percpu_counter {
18 	spinlock_t lock;
19 	long count;
20 	long *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)
30 {
31 	spin_lock_init(&fbc->lock);
32 	fbc->count = 0;
33 	fbc->counters = alloc_percpu(long);
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, long amount);
42 
43 static inline long percpu_counter_read(struct percpu_counter *fbc)
44 {
45 	return fbc->count;
46 }
47 
48 /*
49  * It is possible for the percpu_counter_read() to return a small negative
50  * number for some counter which should never be negative.
51  */
52 static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
53 {
54 	long ret = fbc->count;
55 
56 	barrier();		/* Prevent reloads of fbc->count */
57 	if (ret > 0)
58 		return ret;
59 	return 1;
60 }
61 
62 #else
63 
64 struct percpu_counter {
65 	long count;
66 };
67 
68 static inline void percpu_counter_init(struct percpu_counter *fbc)
69 {
70 	fbc->count = 0;
71 }
72 
73 static inline void percpu_counter_destroy(struct percpu_counter *fbc)
74 {
75 }
76 
77 static inline void
78 percpu_counter_mod(struct percpu_counter *fbc, long amount)
79 {
80 	preempt_disable();
81 	fbc->count += amount;
82 	preempt_enable();
83 }
84 
85 static inline long percpu_counter_read(struct percpu_counter *fbc)
86 {
87 	return fbc->count;
88 }
89 
90 static inline long percpu_counter_read_positive(struct percpu_counter *fbc)
91 {
92 	return fbc->count;
93 }
94 
95 #endif	/* CONFIG_SMP */
96 
97 static inline void percpu_counter_inc(struct percpu_counter *fbc)
98 {
99 	percpu_counter_mod(fbc, 1);
100 }
101 
102 static inline void percpu_counter_dec(struct percpu_counter *fbc)
103 {
104 	percpu_counter_mod(fbc, -1);
105 }
106 
107 #endif /* _LINUX_PERCPU_COUNTER_H */
108