zram: idle writeback fixes and cleanup

This patch includes some fixes and cleanup for idle-page writeback.

1. writeback_limit interface

Now writeback_limit interface is rather conusing.  For example, once
writeback limit budget is exausted, admin can see 0 from
/sys/block/zramX/writeback_limit which is same semantic with disable
writeback_limit at this moment.  IOW, admin cannot tell that zero came
from disable writeback limit or exausted writeback limit.

To make the interface clear, let's sepatate enable of writeback limit to
another knob - /sys/block/zram0/writeback_limit_enable

* before:
  while true :
    # to re-enable writeback limit once previous one is used up
    echo 0 > /sys/block/zram0/writeback_limit
    echo $((200<<20)) > /sys/block/zram0/writeback_limit
    ..
    .. # used up the writeback limit budget

* new
  # To enable writeback limit, from the beginning, admin should
  # enable it.
  echo $((200<<20)) > /sys/block/zram0/writeback_limit
  echo 1 > /sys/block/zram/0/writeback_limit_enable
  while true :
    echo $((200<<20)) > /sys/block/zram0/writeback_limit
    ..
    .. # used up the writeback limit budget

It's much strightforward.

2. fix condition check idle/huge writeback mode check

The mode in writeback_store is not bit opeartion any more so no need to
use bit operations.  Furthermore, current condition check is broken in
that it does writeback every pages regardless of huge/idle.

3. clean up idle_store

No need to use goto.

[minchan@kernel.org: missed spin_lock_init]
  Link: http://lkml.kernel.org/r/20190103001601.GA255139@google.com
Link: http://lkml.kernel.org/r/20181224033529.19450-1-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Suggested-by: John Dias <joaodias@google.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: John Dias <joaodias@google.com>
Cc: Srinivas Paladugu <srnvs@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 69 insertions, 26 deletions

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 33c5cc879f24..04ca65912638 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -316,11 +316,9 @@ static ssize_t idle_store(struct device *dev,
 		 * See the comment in writeback_store.
 		 */
 		zram_slot_lock(zram, index);
-		if (!zram_allocated(zram, index) ||
-				zram_test_flag(zram, index, ZRAM_UNDER_WB))
-			goto next;
-		zram_set_flag(zram, index, ZRAM_IDLE);
-next:
+		if (zram_allocated(zram, index) &&
+				!zram_test_flag(zram, index, ZRAM_UNDER_WB))
+			zram_set_flag(zram, index, ZRAM_IDLE);
 		zram_slot_unlock(zram, index);
 	}
 
@@ -330,6 +328,41 @@ next:
 }
 
 #ifdef CONFIG_ZRAM_WRITEBACK
+static ssize_t writeback_limit_enable_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);
+	spin_lock(&zram->wb_limit_lock);
+	zram->wb_limit_enable = val;
+	spin_unlock(&zram->wb_limit_lock);
+	up_read(&zram->init_lock);
+	ret = len;
+
+	return ret;
+}
+
+static ssize_t writeback_limit_enable_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	bool val;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	spin_lock(&zram->wb_limit_lock);
+	val = zram->wb_limit_enable;
+	spin_unlock(&zram->wb_limit_lock);
+	up_read(&zram->init_lock);
+
+	return scnprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+
 static ssize_t writeback_limit_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
@@ -341,9 +374,9 @@ static ssize_t writeback_limit_store(struct device *dev,
 		return ret;
 
 	down_read(&zram->init_lock);
-	atomic64_set(&zram->stats.bd_wb_limit, val);
-	if (val == 0)
-		zram->stop_writeback = false;
+	spin_lock(&zram->wb_limit_lock);
+	zram->bd_wb_limit = val;
+	spin_unlock(&zram->wb_limit_lock);
 	up_read(&zram->init_lock);
 	ret = len;
 
@@ -357,7 +390,9 @@ static ssize_t writeback_limit_show(struct device *dev,
 	struct zram *zram = dev_to_zram(dev);
 
 	down_read(&zram->init_lock);
-	val = atomic64_read(&zram->stats.bd_wb_limit);
+	spin_lock(&zram->wb_limit_lock);
+	val = zram->bd_wb_limit;
+	spin_unlock(&zram->wb_limit_lock);
 	up_read(&zram->init_lock);
 
 	return scnprintf(buf, PAGE_SIZE, "%llu\n", val);
@@ -588,8 +623,8 @@ static int read_from_bdev_async(struct zram *zram, struct bio_vec *bvec,
 	return 1;
 }
 
-#define HUGE_WRITEBACK 0x1
-#define IDLE_WRITEBACK 0x2
+#define HUGE_WRITEBACK 1
+#define IDLE_WRITEBACK 2
 
 static ssize_t writeback_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
@@ -602,7 +637,7 @@ static ssize_t writeback_store(struct device *dev,
 	struct page *page;
 	ssize_t ret, sz;
 	char mode_buf[8];
-	unsigned long mode = -1UL;
+	int mode = -1;
 	unsigned long blk_idx = 0;
 
 	sz = strscpy(mode_buf, buf, sizeof(mode_buf));
@@ -618,7 +653,7 @@ static ssize_t writeback_store(struct device *dev,
 	else if (!strcmp(mode_buf, "huge"))
 		mode = HUGE_WRITEBACK;
 
-	if (mode == -1UL)
+	if (mode == -1)
 		return -EINVAL;
 
 	down_read(&zram->init_lock);
@@ -645,10 +680,13 @@ static ssize_t writeback_store(struct device *dev,
 		bvec.bv_len = PAGE_SIZE;
 		bvec.bv_offset = 0;
 
-		if (zram->stop_writeback) {
+		spin_lock(&zram->wb_limit_lock);
+		if (zram->wb_limit_enable && !zram->bd_wb_limit) {
+			spin_unlock(&zram->wb_limit_lock);
 			ret = -EIO;
 			break;
 		}
+		spin_unlock(&zram->wb_limit_lock);
 
 		if (!blk_idx) {
 			blk_idx = alloc_block_bdev(zram);
@@ -667,10 +705,11 @@ static ssize_t writeback_store(struct device *dev,
 				zram_test_flag(zram, index, ZRAM_UNDER_WB))
 			goto next;
 
-		if ((mode & IDLE_WRITEBACK &&
-			  !zram_test_flag(zram, index, ZRAM_IDLE)) &&
-		    (mode & HUGE_WRITEBACK &&
-			  !zram_test_flag(zram, index, ZRAM_HUGE)))
+		if (mode == IDLE_WRITEBACK &&
+			  !zram_test_flag(zram, index, ZRAM_IDLE))
+			goto next;
+		if (mode == HUGE_WRITEBACK &&
+			  !zram_test_flag(zram, index, ZRAM_HUGE))
 			goto next;
 		/*
 		 * Clearing ZRAM_UNDER_WB is duty of caller.
@@ -732,11 +771,10 @@ 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;
-		}
+		spin_lock(&zram->wb_limit_lock);
+		if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
+			zram->bd_wb_limit -=  1UL << (PAGE_SHIFT - 12);
+		spin_unlock(&zram->wb_limit_lock);
 next:
 		zram_slot_unlock(zram, index);
 	}
@@ -1812,6 +1850,7 @@ static DEVICE_ATTR_RW(comp_algorithm);
 static DEVICE_ATTR_RW(backing_dev);
 static DEVICE_ATTR_WO(writeback);
 static DEVICE_ATTR_RW(writeback_limit);
+static DEVICE_ATTR_RW(writeback_limit_enable);
 #endif
 
 static struct attribute *zram_disk_attrs[] = {
@@ -1828,6 +1867,7 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_backing_dev.attr,
 	&dev_attr_writeback.attr,
 	&dev_attr_writeback_limit.attr,
+	&dev_attr_writeback_limit_enable.attr,
 #endif
 	&dev_attr_io_stat.attr,
 	&dev_attr_mm_stat.attr,
@@ -1867,7 +1907,9 @@ static int zram_add(void)
 	device_id = ret;
 
 	init_rwsem(&zram->init_lock);
-
+#ifdef CONFIG_ZRAM_WRITEBACK
+	spin_lock_init(&zram->wb_limit_lock);
+#endif
 	queue = blk_alloc_queue(GFP_KERNEL);
 	if (!queue) {
 		pr_err("Error allocating disk queue for device %d\n",
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 4bd3afd15e83..f2fd46daa760 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -86,7 +86,6 @@ 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
 };
 
@@ -114,8 +113,10 @@ struct zram {
 	 */
 	bool claim; /* Protected by bdev->bd_mutex */
 	struct file *backing_dev;
-	bool stop_writeback;
 #ifdef CONFIG_ZRAM_WRITEBACK
+	spinlock_t wb_limit_lock;
+	bool wb_limit_enable;
+	u64 bd_wb_limit;
 	struct block_device *bdev;
 	unsigned int old_block_size;
 	unsigned long *bitmap;