zram: writeback throttle

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" for 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.

[minchan@kernel.org: v4]
  Link: http://lkml.kernel.org/r/20181203024045.153534-8-minchan@kernel.org
Link: http://lkml.kernel.org/r/20181127055429.251614-8-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Joey Pabalinas <joeypabalinas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 51 insertions, 3 deletions

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 @@ next:
 }
 
 #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;