[PATCH 2/3] zram: limit memory size for zram

[Minchan Kim <minchan@kernel.org>]

Since zram has no control feature to limit memory usage,
it makes hard to manage system memrory.

This patch adds new knob "mem_limit" via sysfs to set up the
limit.

Note: I added the logic in zram, not zsmalloc because the limit
is requirement of zram, not zsmalloc so I'd like to avoid
unnecessary branch in zsmalloc.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 Documentation/blockdev/zram.txt | 20 +++++++++++++++----
 drivers/block/zram/zram_drv.c   | 43 +++++++++++++++++++++++++++++++++++++++++
 drivers/block/zram/zram_drv.h   |  1 +
 3 files changed, 60 insertions(+), 4 deletions(-)

diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 0595c3f56ccf..9f239ff8c444 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -74,14 +74,26 @@ There is little point creating a zram of greater than twice the size of memory
 since we expect a 2:1 compression ratio. Note that zram uses about 0.1% of the
 size of the disk when not in use so a huge zram is wasteful.
 
-5) Activate:
+5) Set memory limit: Optional
+	Set memory limit by writing the value to sysfs node 'mem_limit'.
+	The value can be either in bytes or you can use mem suffixes.
+	Examples:
+	    # limit /dev/zram0 with 50MB memory
+	    echo $((50*1024*1024)) > /sys/block/zram0/mem_limit
+
+	    # Using mem suffixes
+	    echo 256K > /sys/block/zram0/mem_limit
+	    echo 512M > /sys/block/zram0/mem_limit
+	    echo 1G > /sys/block/zram0/mem_limit
+
+6) Activate:
 	mkswap /dev/zram0
 	swapon /dev/zram0
 
 	mkfs.ext4 /dev/zram1
 	mount /dev/zram1 /tmp
 
-6) Stats:
+7) Stats:
 	Per-device statistics are exported as various nodes under
 	/sys/block/zram<id>/
 		disksize
@@ -96,11 +108,11 @@ size of the disk when not in use so a huge zram is wasteful.
 		compr_data_size
 		mem_used_total
 
-7) Deactivate:
+8) Deactivate:
 	swapoff /dev/zram0
 	umount /dev/zram1
 
-8) Reset:
+9) Reset:
 	Write any positive value to 'reset' sysfs node
 	echo 1 > /sys/block/zram0/reset
 	echo 1 > /sys/block/zram1/reset
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index d00831c3d731..b48a3d0e9031 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -122,6 +122,35 @@ 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);
+
+	limit = memparse(buf, NULL);
+	if (!limit)
+		return -EINVAL;
+
+	down_write(&zram->init_lock);
+	zram->limit_bytes = limit;
+	up_write(&zram->init_lock);
+	return len;
+}
+
 static ssize_t max_comp_streams_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
@@ -513,6 +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)) {
@@ -617,6 +654,9 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
 	struct zram_meta *meta;
 
 	down_write(&zram->init_lock);
+
+	zram->limit_bytes = 0;
+
 	if (!init_done(zram)) {
 		up_write(&zram->init_lock);
 		return;
@@ -857,6 +897,8 @@ 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(mem_limit, S_IRUGO | S_IWUSR, 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,
@@ -885,6 +927,7 @@ 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_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 e0f725c87cc6..086c51782e75 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -110,6 +110,7 @@ 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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