[PATCH 6/6] zram: writeback throttle

Minchan Kim
2018-11-16T07:21:02Z

On small memory system, there are lots of write IO so if we use
flash device as swap, there would be serious flash wearout.
To overcome the problem, system developers need to design write
limitation strategy to guarantee flash health for entire product life.

This patch creates a new konb "writeback_limit" on zram. With that,
if current writeback IO count(/sys/block/zramX/io_stat) excceds
the limitation, zram stops further writeback until admin can reset
the limit.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
Documentation/ABI/testing/sysfs-block-zram | 9 ++++
Documentation/blockdev/zram.txt | 2 +
drivers/block/zram/zram_drv.c | 55 ++++++++++++++++++++--
drivers/block/zram/zram_drv.h | 2 +
4 files changed, 65 insertions(+), 3 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-block-zram b/Documentation/ABI/testing/sysfs-block-zram
index a4daca7e5043..210f2cdac752 100644
--- a/Documentation/ABI/testing/sysfs-block-zram
+++ b/Documentation/ABI/testing/sysfs-block-zram
@@ -121,3 +121,12 @@ Contact: Minchan Kim <minchan@kernel.org>
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.
diff --git a/Documentation/blockdev/zram.txt b/Documentation/blockdev/zram.txt
index 1f4907307a0d..39ee416bf552 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
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
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 17d566d9a321..b263febaed10 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -317,6 +317,40 @@ 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 || val > atomic64_read(&zram->stats.bd_writes))
+ 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;
@@ -575,6 +609,7 @@ static ssize_t writeback_store(struct device *dev,
ssize_t ret;
unsigned long mode;
unsigned long blk_idx = 0;
+ u64 wb_count, wb_limit;

#define HUGE_WRITEBACK 0x1
#define IDLE_WRITEBACK 0x2
@@ -610,6 +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) {
@@ -664,7 +704,7 @@ static ssize_t writeback_store(struct device *dev,
continue;
}

- atomic64_inc(&zram->stats.bd_writes);
+ wb_count = atomic64_inc_return(&zram->stats.bd_writes);
/*
* We released zram_slot_lock so need to check if the slot was
* changed. If there is freeing for the slot, we can catch it
@@ -687,6 +727,9 @@ static ssize_t writeback_store(struct device *dev,
zram_set_element(zram, index, blk_idx);
blk_idx = 0;
atomic64_inc(&zram->stats.pages_stored);
+ wb_limit = atomic64_read(&zram->stats.bd_wb_limit);
+ if (wb_limit != 0 && wb_count >= wb_limit)
+ zram->stop_writeback = true;
next:
zram_slot_unlock(zram, index);
}
@@ -765,6 +808,7 @@ static int write_to_bdev(struct zram *zram, struct bio_vec *bvec,
{
struct bio *bio;
unsigned long entry;
+ u64 wb_count, wb_limit;

bio = bio_alloc(GFP_ATOMIC, 1);
if (!bio)
@@ -795,7 +839,10 @@ static int write_to_bdev(struct zram *zram, struct bio_vec *bvec,

submit_bio(bio);
*pentry = entry;
- atomic64_inc(&zram->stats.bd_writes);
+ wb_count = atomic64_inc_return(&zram->stats.bd_writes);
+ wb_limit = atomic64_read(&zram->stats.bd_wb_limit);
+ if (wb_limit != 0 && wb_count >= wb_limit)
+ zram->stop_writeback = true;

return 0;
}
@@ -1319,7 +1366,7 @@ static int __zram_bvec_write(struct zram *zram, struct bio_vec *bvec,
return ret;
}

- if (unlikely(comp_len >= huge_class_size)) {
+ if (unlikely(comp_len >= huge_class_size) && !zram->stop_writeback) {
comp_len = PAGE_SIZE;
if (zram->backing_dev && allow_wb) {
zcomp_stream_put(zram->comp);
@@ -1823,6 +1870,7 @@ 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[] = {
@@ -1838,6 +1886,7 @@ 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 487ff283fb31..41cbd0f7aea8 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 read from backing device */
atomic64_t bd_writes; /* no. of write 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;
--
2.19.1.1215.g8438c0b245-goog