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percpu_counter: new function percpu_counter_sum_and_set

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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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7
lib/percpu_counter.c
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@@ -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;
}