[PATCHv3 3/4] zram: support multi compressing buffers

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

1) Extend zram_comp zcomp_create() with `num_wm' parameter.
`num_wm' limits the number of workmem structs in compression
backend's idle list (max buffers).

2) Introduce zram device attribute max_buffers to show and
store current device's zram_comp max number (num_wm) of workmems.

Usage example:
	echo 4 > /sys/block/zram0/max_buffers

set max_buffers to 4

	cat /sys/block/zram0/max_buffers

show current max_buffers (default value is 1).

iozone -t -T -R -l 3 -u 3 -r 16K -s 60M -I +Z
(write tests. ext4, lzo, each test performed on newly created
 zram0 device)

        test        max_buffers 1    max_buffers 3
---------------------------------------------------
"  Initial write "    631583.39   |    727834.88
"        Rewrite "    456248.23   |   2105054.97
" Mixed workload "   3370016.43   |   3509382.86
"   Random write "    467703.56   |   1953464.78
"         Pwrite "    629146.88   |    775372.46
"         Fwrite "   2573117.39   |   2529637.62

        test        max_buffers 1    max_buffers 3
---------------------------------------------------
"  Initial write "    601112.91   |    765866.05
"        Rewrite "    447834.33   |   2163449.58
" Mixed workload "   2575128.08   |   3257711.77
"   Random write "    461327.45   |   1974731.12
"         Pwrite "    567038.36   |    740242.52
"         Fwrite "   2527107.44   |   2754336.64

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 drivers/block/zram/zram_comp.c | 15 +++++++++------
 drivers/block/zram/zram_comp.h |  2 +-
 drivers/block/zram/zram_drv.c  | 42 +++++++++++++++++++++++++++++++++++++++++-
 drivers/block/zram/zram_drv.h  |  2 +-
 4 files changed, 52 insertions(+), 9 deletions(-)

diff --git a/drivers/block/zram/zram_comp.c b/drivers/block/zram/zram_comp.c
index 139a468..d9b34ba 100644
--- a/drivers/block/zram/zram_comp.c
+++ b/drivers/block/zram/zram_comp.c
@@ -118,11 +118,12 @@ static struct zram_comp_backend *find_backend(const char *compress)
  * allocate new zram_comp and initialize it. return NULL
  * if requested algorithm is not supported or in case
  * of init error */
-struct zram_comp *zcomp_create(const char *compress)
+struct zram_comp *zcomp_create(const char *compress, int num_wm)
 {
 	struct zram_comp *comp;
 	struct zram_comp_backend *backend;
 	struct zcomp_workmem *wm;
+	int i;
 
 	backend = find_backend(compress);
 	if (!backend)
@@ -137,11 +138,13 @@ struct zram_comp *zcomp_create(const char *compress)
 	INIT_LIST_HEAD(&comp->idle_workmem);
 	init_waitqueue_head(&comp->workmem_wait);
 
-	wm = workmem_alloc(comp);
-	if (!wm) {
-		zcomp_destroy(comp);
-		return NULL;
+	for (i = 0; i < num_wm; i++) {
+		wm = workmem_alloc(comp);
+		if (!wm) {
+			zcomp_destroy(comp);
+			return NULL;
+		}
+		list_add_tail(&wm->list, &comp->idle_workmem);
 	}
-	list_add_tail(&wm->list, &comp->idle_workmem);
 	return comp;
 }
diff --git a/drivers/block/zram/zram_comp.h b/drivers/block/zram/zram_comp.h
index 90355e8..277afa0 100644
--- a/drivers/block/zram/zram_comp.h
+++ b/drivers/block/zram/zram_comp.h
@@ -43,7 +43,7 @@ struct zram_comp {
 	struct zram_comp_backend *backend;
 };
 
-struct zram_comp *zcomp_create(const char *comp);
+struct zram_comp *zcomp_create(const char *comp, int num_wm);
 void zcomp_destroy(struct zram_comp *comp);
 
 struct zcomp_workmem *zcomp_workmem_get(struct zram_comp *comp);
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 4875a16..a065c1b 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -107,6 +107,41 @@ static ssize_t mem_used_total_show(struct device *dev,
 	return sprintf(buf, "%llu\n", val);
 }
 
+static ssize_t max_buffers_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	long val;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	val = zram->max_buffers;
+	up_read(&zram->init_lock);
+
+	return sprintf(buf, "%ld\n", val);
+}
+
+static ssize_t max_buffers_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	long num;
+	struct zram *zram = dev_to_zram(dev);
+
+	if (kstrtol(buf, 0, &num))
+		return -EINVAL;
+	if (num < 1 || num > 100)
+		return -EINVAL;
+	down_write(&zram->init_lock);
+	if (init_done(zram)) {
+		up_write(&zram->init_lock);
+		pr_info("Cannot set max buffers for initialized device\n");
+		return -EBUSY;
+	}
+	zram->max_buffers = 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)
@@ -505,6 +540,7 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
 	if (zram->comp)
 		zcomp_destroy(zram->comp);
 	zram->comp = NULL;
+	zram->max_buffers = 1;
 
 	zram_meta_free(zram->meta);
 	zram->meta = NULL;
@@ -534,7 +570,7 @@ static ssize_t disksize_store(struct device *dev,
 		return -EBUSY;
 	}
 
-	zram->comp = zcomp_create(default_compressor);
+	zram->comp = zcomp_create(default_compressor, zram->max_buffers);
 	if (!zram->comp) {
 		up_write(&zram->init_lock);
 		pr_info("Cannot initialise compressing backend\n");
@@ -697,6 +733,8 @@ 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_buffers, S_IRUGO | S_IWUSR,
+		max_buffers_show, max_buffers_store);
 
 ZRAM_ATTR_RO(num_reads);
 ZRAM_ATTR_RO(num_writes);
@@ -721,6 +759,7 @@ 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_buffers.attr,
 	NULL,
 };
 
@@ -784,6 +823,7 @@ static int create_device(struct zram *zram, int device_id)
 
 	zram->meta = NULL;
 	zram->comp = NULL;
+	zram->max_buffers = 1;
 	return 0;
 
 out_free_disk:
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index a2e17d7..68a5421 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 */
-
+	long max_buffers;
 	struct zram_stats stats;
 };
 #endif
-- 
1.9.0.rc3.244.g3497008