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Subject[PATCH 43/52] percpu_counter: new function percpu_counter_sum_and_set
Date
From: Mingming Cao <cmm@us.ibm.com>

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>
---
fs/ext4/balloc.c | 2 +-
include/linux/percpu_counter.h | 12 +++++++++---
lib/percpu_counter.c | 7 ++++++-
3 files changed, 16 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 25f63d8..6369bac 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -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;
diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h
index 9007ccd..2083888 100644
--- a/include/linux/percpu_counter.h
+++ b/include/linux/percpu_counter.h
@@ -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)
diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c
index 1191744..4a8ba4b 100644
--- a/lib/percpu_counter.c
+++ b/lib/percpu_counter.c
@@ -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;
}
--
1.5.6.rc3.1.g36b7.dirty


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