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Commit e8ced39d authored by Mingming Cao's avatar Mingming Cao Committed by Theodore Ts'o
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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: default avatarMingming Cao <cmm@us.ibm.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 64769240

fs/ext4/balloc.c

+1 −1
Original line number Original line Diff line number Diff line
@@ -1621,7 +1621,7 @@ ext4_fsblk_t ext4_has_free_blocks(struct ext4_sb_info *sbi, 
#ifdef CONFIG_SMP

#ifdef CONFIG_SMP

	if (free_blocks - root_blocks < FBC_BATCH)

	if (free_blocks - root_blocks < FBC_BATCH)

		free_blocks =

		free_blocks =

			percpu_counter_sum_positive(&sbi->s_freeblocks_counter);

			percpu_counter_sum_and_set(&sbi->s_freeblocks_counter);

#endif

#endif

	if (free_blocks - root_blocks < nblocks)

	if (free_blocks - root_blocks < nblocks)

		return free_blocks - root_blocks;

		return free_blocks - root_blocks;

include/linux/percpu_counter.h

+9 −3
Original line number Original line Diff line number Diff line
@@ -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_destroy(struct percpu_counter *fbc);

void percpu_counter_set(struct percpu_counter *fbc, s64 amount);

void percpu_counter_set(struct percpu_counter *fbc, s64 amount);

void __percpu_counter_add(struct percpu_counter *fbc, s64 amount, s32 batch);

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)

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)

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;

	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)

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)

static inline s64 percpu_counter_read(struct percpu_counter *fbc)

lib/percpu_counter.c

+6 −1
Original line number Original line Diff line number Diff line
@@ -52,7 +52,7 @@ EXPORT_SYMBOL(__percpu_counter_add); 
 * Add up all the per-cpu counts, return the result.  This is a more accurate

 * Add up all the per-cpu counts, return the result.  This is a more accurate

 * but much slower version of percpu_counter_read_positive()

 * 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;

	s64 ret;

	int cpu;

	int cpu;
@@ -62,7 +62,12 @@ s64 __percpu_counter_sum(struct percpu_counter *fbc) 
	for_each_online_cpu(cpu) {

	for_each_online_cpu(cpu) {

		s32 *pcount = per_cpu_ptr(fbc->counters, cpu);

		s32 *pcount = per_cpu_ptr(fbc->counters, cpu);

		ret += *pcount;

		ret += *pcount;

		if (set)

			*pcount = 0;

	}

	}

	if (set)

		fbc->count = ret;



	spin_unlock(&fbc->lock);

	spin_unlock(&fbc->lock);

	return ret;

	return ret;

}

}