[PATCH RFC 2/7] zram: Add recompression algorithm sysfs knob

[Sergey Senozhatsky <senozhatsky@chromium.org>]

Introduce recomp_algorithm sysfs knob that controls
secondary algorithm selection used for recompression.
This device attribute works in a similar way with
comp_algorithm attribute.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
---
 drivers/block/zram/zram_drv.c | 111 +++++++++++++++++++++++++++-------
 1 file changed, 90 insertions(+), 21 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 4ad1daa1283e..694c8c426cb2 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -41,7 +41,12 @@ static DEFINE_IDR(zram_index_idr);
 static DEFINE_MUTEX(zram_index_mutex);
 
 static int zram_major;
-static const char *default_compressor = CONFIG_ZRAM_DEF_COMP;
+static const char *default_comp_algs[ZRAM_MAX_ZCOMPS] = {
+	CONFIG_ZRAM_DEF_COMP,
+#ifdef CONFIG_ZRAM_MULTI_COMP
+	"zstd",
+#endif
+};
 
 /* Module params (documentation at end) */
 static unsigned int num_devices = 1;
@@ -1011,31 +1016,37 @@ static ssize_t max_comp_streams_store(struct device *dev,
 	return len;
 }
 
-static ssize_t comp_algorithm_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
+static void comp_algorithm_set(struct zram *zram, u32 idx, const char *alg)
 {
-	size_t sz;
-	struct zram *zram = dev_to_zram(dev);
+	bool default_alg = false;
+	int i;
 
-	down_read(&zram->init_lock);
-	sz = zcomp_available_show(zram->comp_algs[ZRAM_PRIMARY_ZCOMP], buf);
-	up_read(&zram->init_lock);
+	/* Do not kfree() algs that we didn't allocate, IOW the default ones */
+	for (i = 0; i < ZRAM_MAX_ZCOMPS; i++) {
+		if (zram->comp_algs[idx] == default_comp_algs[i]) {
+			default_alg = true;
+			break;
+		}
+	}
 
-	return sz;
+	if (!default_alg)
+		kfree(zram->comp_algs[idx]);
+	zram->comp_algs[idx] = alg;
 }
 
-static void comp_algorithm_set(struct zram *zram, u32 idx, const char *alg)
+static ssize_t __comp_algorithm_show(struct zram *zram, u32 idx, char *buf)
 {
-	/* Do not kfree() algs that we didn't allocate, IOW the default ones */
-	if (zram->comp_algs[idx] != default_compressor)
-		kfree(zram->comp_algs[idx]);
-	zram->comp_algs[idx] = alg;
+	ssize_t sz;
+
+	down_read(&zram->init_lock);
+	sz = zcomp_available_show(zram->comp_algs[idx], buf);
+	up_read(&zram->init_lock);
+
+	return sz;
 }
 
-static ssize_t comp_algorithm_store(struct device *dev,
-		struct device_attribute *attr, const char *buf, size_t len)
+static int __comp_algorithm_store(struct zram *zram, u32 idx, const char *buf)
 {
-	struct zram *zram = dev_to_zram(dev);
 	char *compressor;
 	size_t sz;
 
@@ -1064,11 +1075,55 @@ static ssize_t comp_algorithm_store(struct device *dev,
 		return -EBUSY;
 	}
 
-	comp_algorithm_set(zram, ZRAM_PRIMARY_ZCOMP, compressor);
+	comp_algorithm_set(zram, idx, compressor);
 	up_write(&zram->init_lock);
-	return len;
+	return 0;
+}
+
+static ssize_t comp_algorithm_show(struct device *dev,
+				   struct device_attribute *attr,
+				   char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+
+	return __comp_algorithm_show(zram, ZRAM_PRIMARY_ZCOMP, buf);
+}
+
+static ssize_t comp_algorithm_store(struct device *dev,
+				    struct device_attribute *attr,
+				    const char *buf,
+				    size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	int ret;
+
+	ret = __comp_algorithm_store(zram, ZRAM_PRIMARY_ZCOMP, buf);
+	return ret ? ret : len;
 }
 
+#ifdef CONFIG_ZRAM_MULTI_COMP
+static ssize_t recomp_algorithm_show(struct device *dev,
+				     struct device_attribute *attr,
+				     char *buf)
+{
+	struct zram *zram = dev_to_zram(dev);
+
+	return __comp_algorithm_show(zram, ZRAM_SECONDARY_ZCOMP, buf);
+}
+
+static ssize_t recomp_algorithm_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf,
+				      size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	int ret;
+
+	ret = __comp_algorithm_store(zram, ZRAM_SECONDARY_ZCOMP, buf);
+	return ret ? ret : len;
+}
+#endif
+
 static ssize_t compact_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
@@ -1770,7 +1825,11 @@ static void zram_reset_device(struct zram *zram)
 	memset(&zram->stats, 0, sizeof(zram->stats));
 	reset_bdev(zram);
 
-	comp_algorithm_set(zram, ZRAM_PRIMARY_ZCOMP, default_compressor);
+	comp_algorithm_set(zram, ZRAM_PRIMARY_ZCOMP,
+			   default_comp_algs[ZRAM_PRIMARY_ZCOMP]);
+	if (IS_ENABLED(CONFIG_ZRAM_MULTI_COMP))
+		comp_algorithm_set(zram, ZRAM_SECONDARY_ZCOMP,
+				   default_comp_algs[ZRAM_SECONDARY_ZCOMP]);
 	up_write(&zram->init_lock);
 }
 
@@ -1912,6 +1971,9 @@ static DEVICE_ATTR_WO(writeback);
 static DEVICE_ATTR_RW(writeback_limit);
 static DEVICE_ATTR_RW(writeback_limit_enable);
 #endif
+#ifdef CONFIG_ZRAM_MULTI_COMP
+static DEVICE_ATTR_RW(recomp_algorithm);
+#endif
 
 static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_disksize.attr,
@@ -1935,6 +1997,9 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_bd_stat.attr,
 #endif
 	&dev_attr_debug_stat.attr,
+#ifdef CONFIG_ZRAM_MULTI_COMP
+	&dev_attr_recomp_algorithm.attr,
+#endif
 	NULL,
 };
 
@@ -2014,7 +2079,11 @@ static int zram_add(void)
 	if (ret)
 		goto out_cleanup_disk;
 
-	zram->comp_algs[ZRAM_PRIMARY_ZCOMP] = default_compressor;
+	zram->comp_algs[ZRAM_PRIMARY_ZCOMP] =
+		default_comp_algs[ZRAM_PRIMARY_ZCOMP];
+	if (IS_ENABLED(CONFIG_ZRAM_MULTI_COMP))
+		zram->comp_algs[ZRAM_SECONDARY_ZCOMP] =
+			default_comp_algs[ZRAM_SECONDARY_ZCOMP];
 
 	zram_debugfs_register(zram);
 	pr_info("Added device: %s\n", zram->disk->disk_name);
-- 
2.37.2.789.g6183377224-goog