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percpu_counter: new function percpu_counter_sum_and_set 

Delayed allocation need to check free blocks at every write time.
percpu_counter_read_positive() is not quit accurate. delayed
allocation need a more accurate accounting, but using
percpu_counter_sum_positive() is frequently is quite expensive.

This patch added a new function to update center counter when sum
per-cpu counter, to increase the accurate rate for next
percpu_counter_read() and require less calling expensive
percpu_counter_sum().

Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Mingming Cao 2008-07-11 19:27:31 -04:00 committed by Theodore Ts'o
parent 64769240bd
commit e8ced39d5e
3 changed files with 16 additions and 5 deletions
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2
fs/ext4/balloc.c
View File

@ -1621,7 +1621,7 @@ ext4_fsblk_t ext4_has_free_blocks(struct ext4_sb_info *sbi,
#ifdef CONFIG_SMP
if (free_blocks - root_blocks < FBC_BATCH)
free_blocks =
percpu_counter_sum_positive(&sbi->s_freeblocks_counter);
percpu_counter_sum_and_set(&sbi->s_freeblocks_counter);
#endif
if (free_blocks - root_blocks < nblocks)
return free_blocks - root_blocks;

12
include/linux/percpu_counter.h
View File

@ -35,7 +35,7 @@ int percpu_counter_init_irq(struct percpu_counter *fbc, s64 amount);
void percpu_counter_destroy(struct percpu_counter *fbc);
void percpu_counter_set(struct percpu_counter *fbc, s64 amount);
void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch);
s64 __percpu_counter_sum(struct percpu_counter *fbc);
s64 __percpu_counter_sum(struct percpu_counter *fbc, int set);
static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
{
@ -44,13 +44,19 @@ static inline void percpu_counter_add(struct percpu_counter *fbc, s64 amount)
static inline s64 percpu_counter_sum_positive(struct percpu_counter *fbc)
{
s64 ret = __percpu_counter_sum(fbc);
s64 ret = __percpu_counter_sum(fbc, 0);
return ret < 0 ? 0 : ret;
}
static inline s64 percpu_counter_sum_and_set(struct percpu_counter *fbc)
{
return __percpu_counter_sum(fbc, 1);
}
static inline s64 percpu_counter_sum(struct percpu_counter *fbc)
{
return __percpu_counter_sum(fbc);
return __percpu_counter_sum(fbc, 0);
}
static inline s64 percpu_counter_read(struct percpu_counter *fbc)

7
lib/percpu_counter.c
View File

@ -52,7 +52,7 @@ EXPORT_SYMBOL(__percpu_counter_add);
* Add up all the per-cpu counts, return the result. This is a more accurate
* but much slower version of percpu_counter_read_positive()
*/
s64 __percpu_counter_sum(struct percpu_counter *fbc)
s64 __percpu_counter_sum(struct percpu_counter *fbc, int set)
{
s64 ret;
int cpu;
@ -62,7 +62,12 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc)
for_each_online_cpu(cpu) {
s32 *pcount = per_cpu_ptr(fbc->counters, cpu);
ret += *pcount;
if (set)
*pcount = 0;
}
if (set)
fbc->count = ret;
spin_unlock(&fbc->lock);
return ret;
}