UPSTREAM: zram: writeback throttle (e610df0c) · Commits · e / devices / android_kernel_fairphone_FP4

Documentation/ABI/testing/sysfs-block-zram

+9 −0

Original line number	Diff line number	Diff line
		@@ -121,3 +121,12 @@ Description:
		The bd_stat file is read-only and represents backing device's
		statistics (bd_count, bd_reads, bd_writes) in a format
		similar to block layer statistics file format.

		What: /sys/block/zram<id>/writeback_limit
		Date: November 2018
		Contact: Minchan Kim <minchan@kernel.org>
		Description:
		The writeback_limit file is read-write and specifies the maximum
		amount of writeback ZRAM can do. The limit could be changed
		in run time and "0" means disable the limit.
		No limit is the initial state.

Documentation/blockdev/zram.txt

+31 −0

Original line number	Diff line number	Diff line
		@@ -164,6 +164,8 @@ reset WO trigger device reset
		mem_used_max WO reset the `mem_used_max' counter (see later)
		mem_limit WO specifies the maximum amount of memory ZRAM can use
		to store the compressed data
		writeback_limit WO specifies the maximum amount of write IO zram can
		write out to backing device as 4KB unit
		max_comp_streams RW the number of possible concurrent compress operations
		comp_algorithm RW show and change the compression algorithm
		compact WO trigger memory compaction
		@@ -275,6 +277,35 @@ Admin can request writeback of those idle pages at right timing via

		With the command, zram writeback idle pages from memory to the storage.

		If there are lots of write IO with flash device, potentially, it has
		flash wearout problem so that admin needs to design write limitation
		to guarantee storage health for entire product life.
		To overcome the concern, zram supports "writeback_limit".
		The "writeback_limit"'s default value is 0 so that it doesn't limit
		any writeback. If admin want to measure writeback count in a certain
		period, he could know it via /sys/block/zram0/bd_stat's 3rd column.

		If admin want to limit writeback as per-day 400M, he could do it
		like below.

		MB_SHIFT=20
		4K_SHIFT=12
		echo $((400<<MB_SHIFT>>4K_SHIFT)) > \
		/sys/block/zram0/writeback_limit.

		If admin want to allow further write again, he could do it like below

		echo 0 > /sys/block/zram0/writeback_limit

		If admin want to see remaining writeback budget since he set,

		cat /sys/block/zram0/writeback_limit

		The writeback_limit count will reset whenever you reset zram(e.g.,
		system reboot, echo 1 > /sys/block/zramX/reset) so keeping how many of
		writeback happened until you reset the zram to allocate extra writeback
		budget in next setting is user's job.

		= memory tracking

		With CONFIG_ZRAM_MEMORY_TRACKING, user can know information of the

drivers/block/zram/zram_drv.c

+49 −3

Original line number	Diff line number	Diff line
		@@ -330,6 +330,39 @@ static ssize_t idle_store(struct device *dev,
		}

		#ifdef CONFIG_ZRAM_WRITEBACK
		static ssize_t writeback_limit_store(struct device *dev,
		struct device_attribute attr, const char buf, size_t len)
		{
		struct zram *zram = dev_to_zram(dev);
		u64 val;
		ssize_t ret = -EINVAL;

		if (kstrtoull(buf, 10, &val))
		return ret;

		down_read(&zram->init_lock);
		atomic64_set(&zram->stats.bd_wb_limit, val);
		if (val == 0)
		zram->stop_writeback = false;
		up_read(&zram->init_lock);
		ret = len;

		return ret;
		}

		static ssize_t writeback_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 = atomic64_read(&zram->stats.bd_wb_limit);
		up_read(&zram->init_lock);

		return scnprintf(buf, PAGE_SIZE, "%llu\n", val);
		}

		static void reset_bdev(struct zram *zram)
		{
		struct block_device *bdev;
		@@ -612,6 +645,11 @@ static ssize_t writeback_store(struct device *dev,
		bvec.bv_len = PAGE_SIZE;
		bvec.bv_offset = 0;

		if (zram->stop_writeback) {
		ret = -EIO;
		break;
		}

		if (!blk_idx) {
		blk_idx = alloc_block_bdev(zram);
		if (!blk_idx) {
		@@ -694,6 +732,11 @@ static ssize_t writeback_store(struct device *dev,
		zram_set_element(zram, index, blk_idx);
		blk_idx = 0;
		atomic64_inc(&zram->stats.pages_stored);
		if (atomic64_add_unless(&zram->stats.bd_wb_limit,
		-1 << (PAGE_SHIFT - 12), 0)) {
		if (atomic64_read(&zram->stats.bd_wb_limit) == 0)
		zram->stop_writeback = true;
		}
		next:
		zram_slot_unlock(zram, index);
		}
		@@ -1018,6 +1061,7 @@ static ssize_t mm_stat_show(struct device *dev,
		}

		#ifdef CONFIG_ZRAM_WRITEBACK
		#define FOUR_K(x) ((x) * (1 << (PAGE_SHIFT - 12)))
		static ssize_t bd_stat_show(struct device *dev,
		struct device_attribute attr, char buf)
		{
		@@ -1027,9 +1071,9 @@ static ssize_t bd_stat_show(struct device *dev,
		down_read(&zram->init_lock);
		ret = scnprintf(buf, PAGE_SIZE,
		"%8llu %8llu %8llu\n",
		(u64)atomic64_read(&zram->stats.bd_count) * (PAGE_SHIFT - 12),
		(u64)atomic64_read(&zram->stats.bd_reads) * (PAGE_SHIFT - 12),
		(u64)atomic64_read(&zram->stats.bd_writes) * (PAGE_SHIFT - 12));
		FOUR_K((u64)atomic64_read(&zram->stats.bd_count)),
		FOUR_K((u64)atomic64_read(&zram->stats.bd_reads)),
		FOUR_K((u64)atomic64_read(&zram->stats.bd_writes)));
		up_read(&zram->init_lock);

		return ret;
		@@ -1767,6 +1811,7 @@ static DEVICE_ATTR_RW(comp_algorithm);
		#ifdef CONFIG_ZRAM_WRITEBACK
		static DEVICE_ATTR_RW(backing_dev);
		static DEVICE_ATTR_WO(writeback);
		static DEVICE_ATTR_RW(writeback_limit);
		#endif

		static struct attribute *zram_disk_attrs[] = {
		@@ -1782,6 +1827,7 @@ static struct attribute *zram_disk_attrs[] = {
		#ifdef CONFIG_ZRAM_WRITEBACK
		&dev_attr_backing_dev.attr,
		&dev_attr_writeback.attr,
		&dev_attr_writeback_limit.attr,
		#endif
		&dev_attr_io_stat.attr,
		&dev_attr_mm_stat.attr,

drivers/block/zram/zram_drv.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -86,6 +86,7 @@ struct zram_stats {
		atomic64_t bd_count; /* no. of pages in backing device */
		atomic64_t bd_reads; /* no. of reads from backing device */
		atomic64_t bd_writes; /* no. of writes from backing device */
		atomic64_t bd_wb_limit; /* writeback limit of backing device */
		#endif
		};

		@@ -113,6 +114,7 @@ struct zram {
		*/
		bool claim; /* Protected by bdev->bd_mutex */
		struct file *backing_dev;
		bool stop_writeback;
		#ifdef CONFIG_ZRAM_WRITEBACK
		struct block_device *bdev;
		unsigned int old_block_size;