[PATCHv7 5/7] zram: enable multi stream compression support in zram

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

1) Introduce zram device attribute max_comp_streams to show and store
current zcomp's max number of zcomp streams (num_strm).

2) Extend zcomp zcomp_create() with `num_strm' parameter. `num_strm'
limits the number of zcomp_strm structs in compression backend's idle
list (max_comp_streams).

max_comp_streams used during initialisation as follows:
-- passing to zcomp_create() num_strm equals to 1 will initialise zcomp
using single compression stream zcomp_strm_single (mutex-based locking).
-- passing to zcomp_create() num_strm greater than 1 will initialise zcomp
using multi compression stream zcomp_strm_multi (spinlock-based locking).

default max_comp_streams value is 1, meaning that zram with single stream
will be initialised.

Later patch will introduce configuration knob to change max_comp_streams
on already initialised and used zcomp.

iozone -t 3 -R -r 16K -s 60M -I +Z

       test           base       1 strm (mutex)     3 strm (spinlock)
-----------------------------------------------------------------------
 Initial write      589286.78       583518.39          718011.05
       Rewrite      604837.97       596776.38         1515125.72
  Random write      584120.11       595714.58         1388850.25
        Pwrite      535731.17       541117.38          739295.27
        Fwrite     1418083.88      1478612.72         1484927.06

Usage example:
set max_comp_streams to 4
        echo 4 > /sys/block/zram0/max_comp_streams

show current max_comp_streams (default value is 1).
        cat /sys/block/zram0/max_comp_streams

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 drivers/block/zram/zcomp.c    |  9 +++++++--
 drivers/block/zram/zcomp.h    |  2 +-
 drivers/block/zram/zram_drv.c | 42 +++++++++++++++++++++++++++++++++++++++++-
 drivers/block/zram/zram_drv.h |  2 +-
 4 files changed, 50 insertions(+), 5 deletions(-)

diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
index 6f238f5..1bcb70e 100644
--- a/drivers/block/zram/zcomp.c
+++ b/drivers/block/zram/zcomp.c
@@ -258,8 +258,9 @@ void zcomp_destroy(struct zcomp *comp)
  * if requested algorithm is not supported or in case
  * of init error
  */
-struct zcomp *zcomp_create(const char *compress)
+struct zcomp *zcomp_create(const char *compress, int num_strm)
 {
+	int ret;
 	struct zcomp *comp;
 	struct zcomp_backend *backend;
 
@@ -272,7 +273,11 @@ struct zcomp *zcomp_create(const char *compress)
 		return NULL;
 
 	comp->backend = backend;
-	if (zcomp_strm_single_create(comp) != 0) {
+	if (num_strm > 1)
+		ret = zcomp_strm_multi_create(comp, num_strm);
+	else
+		ret = zcomp_strm_single_create(comp);
+	if (ret != 0) {
 		zcomp_destroy(comp);
 		return NULL;
 	}
diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
index 861e04d..5514509 100644
--- a/drivers/block/zram/zcomp.h
+++ b/drivers/block/zram/zcomp.h
@@ -42,7 +42,7 @@ struct zcomp {
 	void (*destroy)(struct zcomp *comp);
 };
 
-struct zcomp *zcomp_create(const char *comp);
+struct zcomp *zcomp_create(const char *comp, int num_strm);
 void zcomp_destroy(struct zcomp *comp);
 
 struct zcomp_strm *zcomp_strm_get(struct zcomp *comp);
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 569ff58..42b9c7f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -108,6 +108,40 @@ static ssize_t mem_used_total_show(struct device *dev,
 	return sprintf(buf, "%llu\n", val);
 }
 
+static ssize_t max_comp_streams_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	int val;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	val = zram->max_comp_streams;
+	up_read(&zram->init_lock);
+
+	return sprintf(buf, "%d\n", val);
+}
+
+static ssize_t max_comp_streams_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	int num;
+	struct zram *zram = dev_to_zram(dev);
+
+	if (kstrtoint(buf, 0, &num))
+		return -EINVAL;
+	if (num < 1)
+		return -EINVAL;
+	down_write(&zram->init_lock);
+	if (init_done(zram)) {
+		up_write(&zram->init_lock);
+		pr_info("Can't set max_comp_streams for initialized device\n");
+		return -EBUSY;
+	}
+	zram->max_comp_streams = num;
+	up_write(&zram->init_lock);
+	return len;
+}
+
 /* flag operations needs meta->tb_lock */
 static int zram_test_flag(struct zram_meta *meta, u32 index,
 			enum zram_pageflags flag)
@@ -502,6 +536,8 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
 	}
 
 	zcomp_destroy(zram->comp);
+	zram->max_comp_streams = 1;
+
 	zram_meta_free(zram->meta);
 	zram->meta = NULL;
 	/* Reset stats */
@@ -530,7 +566,7 @@ static ssize_t disksize_store(struct device *dev,
 		return -EBUSY;
 	}
 
-	zram->comp = zcomp_create(default_compressor);
+	zram->comp = zcomp_create(default_compressor, zram->max_comp_streams);
 	if (!zram->comp) {
 		up_write(&zram->init_lock);
 		pr_info("Cannot initialise %s compressing backend\n",
@@ -693,6 +729,8 @@ static DEVICE_ATTR(initstate, S_IRUGO, initstate_show, NULL);
 static DEVICE_ATTR(reset, S_IWUSR, NULL, reset_store);
 static DEVICE_ATTR(orig_data_size, S_IRUGO, orig_data_size_show, NULL);
 static DEVICE_ATTR(mem_used_total, S_IRUGO, mem_used_total_show, NULL);
+static DEVICE_ATTR(max_comp_streams, S_IRUGO | S_IWUSR,
+		max_comp_streams_show, max_comp_streams_store);
 
 ZRAM_ATTR_RO(num_reads);
 ZRAM_ATTR_RO(num_writes);
@@ -717,6 +755,7 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_orig_data_size.attr,
 	&dev_attr_compr_data_size.attr,
 	&dev_attr_mem_used_total.attr,
+	&dev_attr_max_comp_streams.attr,
 	NULL,
 };
 
@@ -779,6 +818,7 @@ static int create_device(struct zram *zram, int device_id)
 	}
 
 	zram->meta = NULL;
+	zram->max_comp_streams = 1;
 	return 0;
 
 out_free_disk:
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 45e04f7..ccf36d1 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -99,7 +99,7 @@ struct zram {
 	 * we can store in a disk.
 	 */
 	u64 disksize;	/* bytes */
-
+	int max_comp_streams;
 	struct zram_stats stats;
 };
 #endif
-- 
1.9.0.291.g027825b