[PATCH v2 1/4] zram: use atomic operation for stat
From: Minchan Kim
Date: Tue Jan 14 2014 - 20:12:30 EST
Some of fields in zram->stats are protected by zram->lock which
is rather coarse-grained so let's use atomic operation without
explict locking.
This patch is ready for removing dependency of zram->lock in
read path which is very coarse-grained rw_semaphore.
Of course, this patch adds new atomic operation so it might make
slow but my 12CPU test couldn't spot any regression.
All gain/lose is marginal within stddev.
iozone -t -T -l 12 -u 12 -r 16K -s 60M -I +Z -V 0
==Initial write ==Initial write
records: 50 records: 50
avg: 412875.17 avg: 415638.23
std: 38543.12 (9.34%) std: 36601.11 (8.81%)
max: 521262.03 max: 502976.72
min: 343263.13 min: 351389.12
==Rewrite ==Rewrite
records: 50 records: 50
avg: 416640.34 avg: 397914.33
std: 60798.92 (14.59%) std: 46150.42 (11.60%)
max: 543057.07 max: 522669.17
min: 304071.67 min: 316588.77
==Read ==Read
records: 50 records: 50
avg: 4147338.63 avg: 4070736.51
std: 179333.25 (4.32%) std: 223499.89 (5.49%)
max: 4459295.28 max: 4539514.44
min: 3753057.53 min: 3444686.31
==Re-read ==Re-read
records: 50 records: 50
avg: 4096706.71 avg: 4117218.57
std: 229735.04 (5.61%) std: 171676.25 (4.17%)
max: 4430012.09 max: 4459263.94
min: 2987217.80 min: 3666904.28
==Reverse Read ==Reverse Read
records: 50 records: 50
avg: 4062763.83 avg: 4078508.32
std: 186208.46 (4.58%) std: 172684.34 (4.23%)
max: 4401358.78 max: 4424757.22
min: 3381625.00 min: 3679359.94
==Stride read ==Stride read
records: 50 records: 50
avg: 4094933.49 avg: 4082170.22
std: 185710.52 (4.54%) std: 196346.68 (4.81%)
max: 4478241.25 max: 4460060.97
min: 3732593.23 min: 3584125.78
==Random read ==Random read
records: 50 records: 50
avg: 4031070.04 avg: 4074847.49
std: 192065.51 (4.76%) std: 206911.33 (5.08%)
max: 4356931.16 max: 4399442.56
min: 3481619.62 min: 3548372.44
==Mixed workload ==Mixed workload
records: 50 records: 50
avg: 149925.73 avg: 149675.54
std: 7701.26 (5.14%) std: 6902.09 (4.61%)
max: 191301.56 max: 175162.05
min: 133566.28 min: 137762.87
==Random write ==Random write
records: 50 records: 50
avg: 404050.11 avg: 393021.47
std: 58887.57 (14.57%) std: 42813.70 (10.89%)
max: 601798.09 max: 524533.43
min: 325176.99 min: 313255.34
==Pwrite ==Pwrite
records: 50 records: 50
avg: 411217.70 avg: 411237.96
std: 43114.99 (10.48%) std: 33136.29 (8.06%)
max: 530766.79 max: 471899.76
min: 320786.84 min: 317906.94
==Pread ==Pread
records: 50 records: 50
avg: 4154908.65 avg: 4087121.92
std: 151272.08 (3.64%) std: 219505.04 (5.37%)
max: 4459478.12 max: 4435857.38
min: 3730512.41 min: 3101101.67
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
drivers/staging/zram/zram_drv.c | 20 ++++++++++----------
drivers/staging/zram/zram_drv.h | 16 ++++++----------
2 files changed, 16 insertions(+), 20 deletions(-)
diff --git a/drivers/staging/zram/zram_drv.c b/drivers/staging/zram/zram_drv.c
index 7889dd6048b9..6613225dfca1 100644
--- a/drivers/staging/zram/zram_drv.c
+++ b/drivers/staging/zram/zram_drv.c
@@ -104,7 +104,7 @@ static ssize_t zero_pages_show(struct device *dev,
{
struct zram *zram = dev_to_zram(dev);
- return sprintf(buf, "%u\n", zram->stats.pages_zero);
+ return sprintf(buf, "%u\n", atomic_read(&zram->stats.pages_zero));
}
static ssize_t orig_data_size_show(struct device *dev,
@@ -113,7 +113,7 @@ static ssize_t orig_data_size_show(struct device *dev,
struct zram *zram = dev_to_zram(dev);
return sprintf(buf, "%llu\n",
- (u64)(zram->stats.pages_stored) << PAGE_SHIFT);
+ (u64)(atomic_read(&zram->stats.pages_stored)) << PAGE_SHIFT);
}
static ssize_t compr_data_size_show(struct device *dev,
@@ -292,21 +292,21 @@ static void zram_free_page(struct zram *zram, size_t index)
*/
if (zram_test_flag(meta, index, ZRAM_ZERO)) {
zram_clear_flag(meta, index, ZRAM_ZERO);
- zram->stats.pages_zero--;
+ atomic_dec(&zram->stats.pages_zero);
}
return;
}
if (unlikely(size > max_zpage_size))
- zram->stats.bad_compress--;
+ atomic_dec(&zram->stats.bad_compress);
zs_free(meta->mem_pool, handle);
if (size <= PAGE_SIZE / 2)
- zram->stats.good_compress--;
+ atomic_dec(&zram->stats.good_compress);
atomic64_sub(meta->table[index].size, &zram->stats.compr_size);
- zram->stats.pages_stored--;
+ atomic_dec(&zram->stats.pages_stored);
meta->table[index].handle = 0;
meta->table[index].size = 0;
@@ -434,7 +434,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
/* Free memory associated with this sector now. */
zram_free_page(zram, index);
- zram->stats.pages_zero++;
+ atomic_inc(&zram->stats.pages_zero);
zram_set_flag(meta, index, ZRAM_ZERO);
ret = 0;
goto out;
@@ -455,7 +455,7 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
}
if (unlikely(clen > max_zpage_size)) {
- zram->stats.bad_compress++;
+ atomic_inc(&zram->stats.bad_compress);
clen = PAGE_SIZE;
src = NULL;
if (is_partial_io(bvec))
@@ -492,9 +492,9 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
/* Update stats */
atomic64_add(clen, &zram->stats.compr_size);
- zram->stats.pages_stored++;
+ atomic_inc(&zram->stats.pages_stored);
if (clen <= PAGE_SIZE / 2)
- zram->stats.good_compress++;
+ atomic_inc(&zram->stats.good_compress);
out:
if (is_partial_io(bvec))
diff --git a/drivers/staging/zram/zram_drv.h b/drivers/staging/zram/zram_drv.h
index 97a3acf6ab76..459483966c3d 100644
--- a/drivers/staging/zram/zram_drv.h
+++ b/drivers/staging/zram/zram_drv.h
@@ -69,10 +69,6 @@ struct table {
u8 flags;
} __aligned(4);
-/*
- * All 64bit fields should only be manipulated by 64bit atomic accessors.
- * All modifications to 32bit counter should be protected by zram->lock.
- */
struct zram_stats {
atomic64_t compr_size; /* compressed size of pages stored */
atomic64_t num_reads; /* failed + successful */
@@ -81,10 +77,10 @@ struct zram_stats {
atomic64_t failed_writes; /* can happen when memory is too low */
atomic64_t invalid_io; /* non-page-aligned I/O requests */
atomic64_t notify_free; /* no. of swap slot free notifications */
- u32 pages_zero; /* no. of zero filled pages */
- u32 pages_stored; /* no. of pages currently stored */
- u32 good_compress; /* % of pages with compression ratio<=50% */
- u32 bad_compress; /* % of pages with compression ratio>=75% */
+ atomic_t pages_zero; /* no. of zero filled pages */
+ atomic_t pages_stored; /* no. of pages currently stored */
+ atomic_t good_compress; /* % of pages with compression ratio<=50% */
+ atomic_t bad_compress; /* % of pages with compression ratio>=75% */
};
struct zram_meta {
@@ -102,8 +98,8 @@ struct zram_slot_free {
struct zram {
struct zram_meta *meta;
struct rw_semaphore lock; /* protect compression buffers, table,
- * 32bit stat counters against concurrent
- * notifications, reads and writes */
+ * reads and writes
+ */
struct work_struct free_work; /* handle pending free request */
struct zram_slot_free *slot_free_rq; /* list head of free request */
--
1.8.5.2
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