[RFC 3/3] zram: limit memory size for zram

[Minchan Kim]

I have received a request several time from zram users.
They want to limit memory size for zram because zram can consume
lot of memory on system without limit so it makes memory management
control hard.

This patch adds new knob to limit memory of zram.

Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
 Documentation/blockdev/zram.txt |  1 +
 drivers/block/zram/zram_drv.c   | 41 +++++++++++++++++++++++++++++++++++++++++
 drivers/block/zram/zram_drv.h   |  1 +
 3 files changed, 43 insertions(+)

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index d24534bee763..fcb0561dfe2e 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -96,6 +96,7 @@ size of the disk when not in use so a huge zram is wasteful.
 		compr_data_size
 		mem_used_total
 		mem_used_max
+		mem_limit
 
 7) Deactivate:
 	swapoff /dev/zram0
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index a4d637b4db7d..47f68bbb2c44 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -137,6 +137,37 @@ static ssize_t max_comp_streams_show(struct device *dev,
 	return scnprintf(buf, PAGE_SIZE, "%d\n", val);
 }
 
+static ssize_t mem_limit_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	u64 val;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	val = zram->limit_bytes;
+	up_read(&zram->init_lock);
+
+	return scnprintf(buf, PAGE_SIZE, "%llu\n", val);
+}
+
+static ssize_t mem_limit_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t len)
+{
+	u64 limit;
+	struct zram *zram = dev_to_zram(dev);
+	int ret;
+
+	ret = kstrtoull(buf, 0, &limit);
+	if (ret < 0)
+		return ret;
+
+	down_write(&zram->init_lock);
+	zram->limit_bytes = limit;
+	ret = len;
+	up_write(&zram->init_lock);
+	return ret;
+}
+
 static ssize_t max_comp_streams_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
@@ -511,6 +542,14 @@ static int zram_bvec_write(struct zram *zram, struct bio_vec *bvec, u32 index,
 		ret = -ENOMEM;
 		goto out;
 	}
+
+	if (zram->limit_bytes &&
+		zs_get_total_size_bytes(meta->mem_pool) >= zram->limit_bytes) {
+		zs_free(meta->mem_pool, handle);
+		ret = -ENOMEM;
+		goto out;
+	}
+
 	cmem = zs_map_object(meta->mem_pool, handle, ZS_MM_WO);
 
 	if ((clen == PAGE_SIZE) && !is_partial_io(bvec)) {
@@ -854,6 +893,7 @@ 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(mem_used_max, S_IRUGO, mem_used_max_show, NULL);
+static DEVICE_ATTR(mem_limit, S_IRUGO, mem_limit_show, mem_limit_store);
 static DEVICE_ATTR(max_comp_streams, S_IRUGO | S_IWUSR,
 		max_comp_streams_show, max_comp_streams_store);
 static DEVICE_ATTR(comp_algorithm, S_IRUGO | S_IWUSR,
@@ -883,6 +923,7 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_compr_data_size.attr,
 	&dev_attr_mem_used_total.attr,
 	&dev_attr_mem_used_max.attr,
+	&dev_attr_mem_limit.attr,
 	&dev_attr_max_comp_streams.attr,
 	&dev_attr_comp_algorithm.attr,
 	NULL,
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 7f21c145e317..c0d497ff6efc 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -99,6 +99,7 @@ struct zram {
 	 * we can store in a disk.
 	 */
 	u64 disksize;	/* bytes */
+	u64 limit_bytes;
 	int max_comp_streams;
 	struct zram_stats stats;
 	char compressor[10];
-- 
2.0.0

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