80188b0d77
XFS uses non-stanard batch sizes for avoiding frequent global counter updates on it's allocated inode counters, as they increment or decrement in batches of 64 inodes. Hence the standard percpu counter batch of 32 means that the counter is effectively a global counter. Currently Xfs uses a batch size of 128 so that it doesn't take the global lock on every single modification. However, Xfs also needs to compare accurately against zero, which means we need to use percpu_counter_compare(), and that has a hard-coded batch size of 32, and hence will spuriously fail to detect when it is supposed to use precise comparisons and hence the accounting goes wrong. Add __percpu_counter_compare() to take a custom batch size so we can use it sanely in XFS and factor percpu_counter_compare() to use it. Signed-off-by: Dave Chinner <dchinner@redhat.com> Acked-by: Tejun Heo <tj@kernel.org> Signed-off-by: Dave Chinner <david@fromorbit.com>
191 lines
4.2 KiB
C
191 lines
4.2 KiB
C
#ifndef _LINUX_PERCPU_COUNTER_H
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#define _LINUX_PERCPU_COUNTER_H
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/*
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* A simple "approximate counter" for use in ext2 and ext3 superblocks.
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*
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* WARNING: these things are HUGE. 4 kbytes per counter on 32-way P4.
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*/
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#include <linux/spinlock.h>
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#include <linux/smp.h>
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#include <linux/list.h>
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#include <linux/threads.h>
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#include <linux/percpu.h>
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#include <linux/types.h>
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#include <linux/gfp.h>
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#ifdef CONFIG_SMP
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struct percpu_counter {
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raw_spinlock_t lock;
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s64 count;
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#ifdef CONFIG_HOTPLUG_CPU
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struct list_head list; /* All percpu_counters are on a list */
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#endif
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s32 __percpu *counters;
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};
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extern int percpu_counter_batch;
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int __percpu_counter_init(struct percpu_counter *fbc, s64 amount, gfp_t gfp,
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struct lock_class_key *key);
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#define percpu_counter_init(fbc, value, gfp) \
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({ \
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static struct lock_class_key __key; \
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\
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__percpu_counter_init(fbc, value, gfp, &__key); \
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})
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void percpu_counter_destroy(struct percpu_counter *fbc);
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void percpu_counter_set(struct percpu_counter *fbc, s64 amount);
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void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch);
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s64 __percpu_counter_sum(struct percpu_counter *fbc);
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int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch);
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static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
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{
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return __percpu_counter_compare(fbc, rhs, percpu_counter_batch);
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}
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static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
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{
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__percpu_counter_add(fbc, amount, percpu_counter_batch);
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}
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static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
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{
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s64 ret = __percpu_counter_sum(fbc);
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return ret < 0 ? 0 : ret;
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}
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static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
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{
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return __percpu_counter_sum(fbc);
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}
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static inline s64 percpu_counter_read(struct percpu_counter *fbc)
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{
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return fbc->count;
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}
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/*
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* It is possible for the percpu_counter_read() to return a small negative
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* number for some counter which should never be negative.
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*
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*/
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static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
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{
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s64 ret = fbc->count;
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barrier(); /* Prevent reloads of fbc->count */
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if (ret >= 0)
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return ret;
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return 0;
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}
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static inline int percpu_counter_initialized(struct percpu_counter *fbc)
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{
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return (fbc->counters != NULL);
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}
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#else /* !CONFIG_SMP */
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struct percpu_counter {
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s64 count;
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};
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static inline int percpu_counter_init(struct percpu_counter *fbc, s64 amount,
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gfp_t gfp)
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{
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fbc->count = amount;
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return 0;
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}
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static inline void percpu_counter_destroy(struct percpu_counter *fbc)
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{
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}
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static inline void percpu_counter_set(struct percpu_counter *fbc, s64 amount)
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{
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fbc->count = amount;
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}
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static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs)
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{
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if (fbc->count > rhs)
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return 1;
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else if (fbc->count < rhs)
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return -1;
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else
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return 0;
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}
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static inline int
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__percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch)
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{
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return percpu_counter_compare(fbc, rhs);
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}
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static inline void
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percpu_counter_add(struct percpu_counter *fbc, s64 amount)
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{
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preempt_disable();
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fbc->count += amount;
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preempt_enable();
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}
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static inline void
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__percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch)
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{
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percpu_counter_add(fbc, amount);
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}
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static inline s64 percpu_counter_read(struct percpu_counter *fbc)
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{
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return fbc->count;
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}
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/*
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* percpu_counter is intended to track positive numbers. In the UP case the
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* number should never be negative.
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*/
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static inline s64 percpu_counter_read_positive(struct percpu_counter *fbc)
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{
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return fbc->count;
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}
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static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
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{
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return percpu_counter_read_positive(fbc);
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}
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static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
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{
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return percpu_counter_read(fbc);
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}
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static inline int percpu_counter_initialized(struct percpu_counter *fbc)
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{
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return 1;
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}
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#endif /* CONFIG_SMP */
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static inline void percpu_counter_inc(struct percpu_counter *fbc)
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{
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percpu_counter_add(fbc, 1);
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}
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static inline void percpu_counter_dec(struct percpu_counter *fbc)
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{
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percpu_counter_add(fbc, -1);
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}
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static inline void percpu_counter_sub(struct percpu_counter *fbc, s64 amount)
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{
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percpu_counter_add(fbc, -amount);
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}
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#endif /* _LINUX_PERCPU_COUNTER_H */
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