2008-06-01 23:36:32

by Mingming Cao

[permalink] [raw]
Subject: [RFC][PATCH 6/6] delalloc ENOSPC: improve percpu counter accounting accurate

percpu counter: update center counter when sum per-cpu counter

From: Mingming cao <[email protected]>

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

This patch added a new function to update center counter when
sum up per-cpu counters, to increase the accurate rate
for next percpu_counter_read()(which reads only the center counter
and require less calling expensive percpu_counter_sum().(in
ext4_has_free_blocks)

Signed-off-by: Mingming cao <[email protected]>

---
fs/ext4/balloc.c | 2 +-
include/linux/percpu_counter.h | 12 +++++++++---
lib/percpu_counter.c | 7 ++++++-
3 files changed, 16 insertions(+), 5 deletions(-)

Index: linux-2.6.26-rc4/include/linux/percpu_counter.h
===================================================================
--- linux-2.6.26-rc4.orig/include/linux/percpu_counter.h 2008-06-01 15:33:09.000000000 -0700
+++ linux-2.6.26-rc4/include/linux/percpu_counter.h 2008-06-01 15:33:14.000000000 -0700
@@ -35,7 +35,7 @@ int percpu_counter_init_irq(struct percp
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(st

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)
Index: linux-2.6.26-rc4/lib/percpu_counter.c
===================================================================
--- linux-2.6.26-rc4.orig/lib/percpu_counter.c 2008-06-01 15:33:09.000000000 -0700
+++ linux-2.6.26-rc4/lib/percpu_counter.c 2008-06-01 15:33:14.000000000 -0700
@@ -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_c
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;
}
Index: linux-2.6.26-rc4/fs/ext4/balloc.c
===================================================================
--- linux-2.6.26-rc4.orig/fs/ext4/balloc.c 2008-06-01 15:33:36.000000000 -0700
+++ linux-2.6.26-rc4/fs/ext4/balloc.c 2008-06-01 15:34:28.000000000 -0700
@@ -1626,7 +1626,7 @@ ext4_fsblk_t ext4_has_free_blocks(struct

if (free_blocks - root_blocks < FBC_BATCH)
free_blocks =
- percpu_counter_sum_positive(&sbi->s_freeblocks_counter);
+ percpu_counter_sum_positive_set(&sbi->s_freeblocks_counter);
if (free_blocks - root_blocks < nblocks )
return free_blocks -root_blocks;
return nblocks;





2008-06-02 00:19:58

by Akira Fujita

[permalink] [raw]
Subject: Re: [RFC][PATCH 6/6] delalloc ENOSPC: improve percpu counter accounting accurate

Hi,

> Mingming Cao wrote:
> percpu counter: update center counter when sum per-cpu counter
>
> From: Mingming cao <[email protected]>
>
> Delayed allocation need to check free blocks at every write time.
> percpu_counter_read_positive() is not quit accurate
> but using percpu_counter_sum_positive() for every write
> frequently is quite expensive.

I couldn't compile the latest ext4 patch qeueu.

LD fs/ext3/ext3.o
LD fs/ext3/built-in.o
CC fs/ext4/balloc.o
fs/ext4/balloc.c: In function ‘ext4_has_free_blocks’:
fs/ext4/balloc.c:1629: error: implicit declaration of function ‘percpu_counter_sum_positive_set’


> + percpu_counter_sum_positive_set(&sbi->s_freeblocks_counter);

Maybe the above line which in percpucounter-add-sum-and-set-function.patch
is percpu_counter_sum_and_set(&sbi->s_freeblocks_couter).

Thanks,
Akira Fujita

2008-06-02 02:30:47

by Mingming Cao

[permalink] [raw]
Subject: Re: [RFC][PATCH 6/6] delalloc ENOSPC: improve percpu counter accounting accurate

On Mon, 2008-06-02 at 09:19 +0900, Akira Fujita wrote:
> Hi,
>
> > Mingming Cao wrote:
> > percpu counter: update center counter when sum per-cpu counter
> >
> > From: Mingming cao <[email protected]>
> >
> > Delayed allocation need to check free blocks at every write time.
> > percpu_counter_read_positive() is not quit accurate
> > but using percpu_counter_sum_positive() for every write
> > frequently is quite expensive.
>
> I couldn't compile the latest ext4 patch qeueu.
>
> LD fs/ext3/ext3.o
> LD fs/ext3/built-in.o
> CC fs/ext4/balloc.o
> fs/ext4/balloc.c: In function ext4_has_free_blocks:
> fs/ext4/balloc.c:1629: error: implicit declaration of function percpu_counter_sum_positive_set
>
>
> > + percpu_counter_sum_positive_set(&sbi->s_freeblocks_counter);
>
> Maybe the above line which in percpucounter-add-sum-and-set-function.patch
> is percpu_counter_sum_and_set(&sbi->s_freeblocks_couter).
>

oops. Updated patch queue, please check again.

Mingming
> Thanks,
> Akira Fujita
> --
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2008-06-02 02:47:15

by Akira Fujita

[permalink] [raw]
Subject: Re: [RFC][PATCH 6/6] delalloc ENOSPC: improve percpu counter accounting accurate

Mingming Cao wrote:
> On Mon, 2008-06-02 at 09:19 +0900, Akira Fujita wrote:
>> Hi,
>>
>>> Mingming Cao wrote:
>>> percpu counter: update center counter when sum per-cpu counter
>>>
>>> From: Mingming cao <[email protected]>
>>>
>>> Delayed allocation need to check free blocks at every write time.
>>> percpu_counter_read_positive() is not quit accurate
>>> but using percpu_counter_sum_positive() for every write
>>> frequently is quite expensive.
>> I couldn't compile the latest ext4 patch qeueu.
>>
>> LD fs/ext3/ext3.o
>> LD fs/ext3/built-in.o
>> CC fs/ext4/balloc.o
>> fs/ext4/balloc.c: In function ext4_has_free_blocks:
>> fs/ext4/balloc.c:1629: error: implicit declaration of function percpu_counter_sum_positive_set
>>
>>
>>> + percpu_counter_sum_positive_set(&sbi->s_freeblocks_counter);
>> Maybe the above line which in percpucounter-add-sum-and-set-function.patch
>> is percpu_counter_sum_and_set(&sbi->s_freeblocks_couter).
>>
>
> oops. Updated patch queue, please check again.

I confirmed that I could compile the latest ext4 patch queue correctly.
Thanks. :-)

Regards,
Akira Fujita