[PATCH v4 7/7] zram: writeback throttle
From: Minchan Kim
Date: Sun Dec 02 2018 - 21:41:20 EST
If there are lots of write IO with flash device, it could have a
wearout problem of storage. To overcome the problem, admin needs
to design write limitation to guarantee flash health
for entire product life.
This patch creates a new knob "writeback_limit" on zram.
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,
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.
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
I removed Reviewed-by from Sergey and Joey because I modified interface
since they had reviewed.
Documentation/ABI/testing/sysfs-block-zram | 9 ++++
Documentation/blockdev/zram.txt | 31 +++++++++++++
drivers/block/zram/zram_drv.c | 52 ++++++++++++++++++++--
drivers/block/zram/zram_drv.h | 2 +
4 files changed, 91 insertions(+), 3 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index 65fc33b2f53b..9d2339a485c8 100644
--- a/Documentation/ABI/testing/sysfs-block-zram
+++ b/Documentation/ABI/testing/sysfs-block-zram
@@ -121,3 +121,12 @@ Contact: Minchan Kim <minchan@xxxxxxxxxx>
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@xxxxxxxxxx>
+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.
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 906df97527a7..436c5e98e1b6 100644
--- a/Documentation/blockdev/zram.txt
+++ b/Documentation/blockdev/zram.txt
@@ -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
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index f1832fa3ba41..33c5cc879f24 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -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,
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index bc477803530d..4bd3afd15e83 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -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;
--
2.20.0.rc1.387.gf8505762e3-goog