2 files changed, 376 insertions, 109 deletions

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index a43074657531..5759823d6314 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -500,8 +500,31 @@ out:
 }
 
 #ifdef CONFIG_ZRAM_WRITEBACK
+#define INVALID_BDEV_BLOCK		(~0UL)
+
+struct zram_wb_ctl {
+	/* idle list is accessed only by the writeback task, no concurency */
+	struct list_head idle_reqs;
+	/* done list is accessed concurrently, protect by done_lock */
+	struct list_head done_reqs;
+	wait_queue_head_t done_wait;
+	spinlock_t done_lock;
+	atomic_t num_inflight;
+};
+
+struct zram_wb_req {
+	unsigned long blk_idx;
+	struct page *page;
+	struct zram_pp_slot *pps;
+	struct bio_vec bio_vec;
+	struct bio bio;
+
+	struct list_head entry;
+};
+
 static ssize_t writeback_limit_enable_store(struct device *dev,
-		struct device_attribute *attr, const char *buf, size_t len)
+					    struct device_attribute *attr,
+					    const char *buf, size_t len)
 {
 	struct zram *zram = dev_to_zram(dev);
 	u64 val;
@@ -510,33 +533,31 @@ static ssize_t writeback_limit_enable_store(struct device *dev,
 	if (kstrtoull(buf, 10, &val))
 		return ret;
 
-	down_read(&zram->init_lock);
-	spin_lock(&zram->wb_limit_lock);
+	down_write(&zram->init_lock);
 	zram->wb_limit_enable = val;
-	spin_unlock(&zram->wb_limit_lock);
-	up_read(&zram->init_lock);
+	up_write(&zram->init_lock);
 	ret = len;
 
 	return ret;
 }
 
 static ssize_t writeback_limit_enable_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
+					   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 sysfs_emit(buf, "%d\n", val);
 }
 
 static ssize_t writeback_limit_store(struct device *dev,
-		struct device_attribute *attr, const char *buf, size_t len)
+				     struct device_attribute *attr,
+				     const char *buf, size_t len)
 {
 	struct zram *zram = dev_to_zram(dev);
 	u64 val;
@@ -545,31 +566,71 @@ static ssize_t writeback_limit_store(struct device *dev,
 	if (kstrtoull(buf, 10, &val))
 		return ret;
 
-	down_read(&zram->init_lock);
-	spin_lock(&zram->wb_limit_lock);
+	/*
+	 * When the page size is greater than 4KB, if bd_wb_limit is set to
+	 * a value that is not page - size aligned, it will cause value
+	 * wrapping. For example, when the page size is set to 16KB and
+	 * bd_wb_limit is set to 3, a single write - back operation will
+	 * cause bd_wb_limit to become -1. Even more terrifying is that
+	 * bd_wb_limit is an unsigned number.
+	 */
+	val = rounddown(val, PAGE_SIZE / 4096);
+
+	down_write(&zram->init_lock);
 	zram->bd_wb_limit = val;
-	spin_unlock(&zram->wb_limit_lock);
-	up_read(&zram->init_lock);
+	up_write(&zram->init_lock);
 	ret = len;
 
 	return ret;
 }
 
 static ssize_t writeback_limit_show(struct device *dev,
-		struct device_attribute *attr, char *buf)
+				    struct device_attribute *attr, char *buf)
 {
 	u64 val;
 	struct zram *zram = dev_to_zram(dev);
 
 	down_read(&zram->init_lock);
-	spin_lock(&zram->wb_limit_lock);
 	val = zram->bd_wb_limit;
-	spin_unlock(&zram->wb_limit_lock);
 	up_read(&zram->init_lock);
 
 	return sysfs_emit(buf, "%llu\n", val);
 }
 
+static ssize_t writeback_batch_size_store(struct device *dev,
+					  struct device_attribute *attr,
+					  const char *buf, size_t len)
+{
+	struct zram *zram = dev_to_zram(dev);
+	u32 val;
+
+	if (kstrtouint(buf, 10, &val))
+		return -EINVAL;
+
+	if (!val)
+		return -EINVAL;
+
+	down_write(&zram->init_lock);
+	zram->wb_batch_size = val;
+	up_write(&zram->init_lock);
+
+	return len;
+}
+
+static ssize_t writeback_batch_size_show(struct device *dev,
+					 struct device_attribute *attr,
+					 char *buf)
+{
+	u32 val;
+	struct zram *zram = dev_to_zram(dev);
+
+	down_read(&zram->init_lock);
+	val = zram->wb_batch_size;
+	up_read(&zram->init_lock);
+
+	return sysfs_emit(buf, "%u\n", val);
+}
+
 static void reset_bdev(struct zram *zram)
 {
 	if (!zram->backing_dev)
@@ -697,23 +758,20 @@ out:
 	return err;
 }
 
-static unsigned long alloc_block_bdev(struct zram *zram)
+static unsigned long zram_reserve_bdev_block(struct zram *zram)
 {
-	unsigned long blk_idx = 1;
-retry:
-	/* skip 0 bit to confuse zram.handle = 0 */
-	blk_idx = find_next_zero_bit(zram->bitmap, zram->nr_pages, blk_idx);
-	if (blk_idx == zram->nr_pages)
-		return 0;
+	unsigned long blk_idx;
 
-	if (test_and_set_bit(blk_idx, zram->bitmap))
-		goto retry;
+	blk_idx = find_next_zero_bit(zram->bitmap, zram->nr_pages, 0);
+	if (blk_idx == zram->nr_pages)
+		return INVALID_BDEV_BLOCK;
 
+	set_bit(blk_idx, zram->bitmap);
 	atomic64_inc(&zram->stats.bd_count);
 	return blk_idx;
 }
 
-static void free_block_bdev(struct zram *zram, unsigned long blk_idx)
+static void zram_release_bdev_block(struct zram *zram, unsigned long blk_idx)
 {
 	int was_set;
 
@@ -734,32 +792,249 @@ static void read_from_bdev_async(struct zram *zram, struct page *page,
 	submit_bio(bio);
 }
 
-static int zram_writeback_slots(struct zram *zram, struct zram_pp_ctl *ctl)
+static void release_wb_req(struct zram_wb_req *req)
 {
-	unsigned long blk_idx = 0;
-	struct page *page = NULL;
-	struct zram_pp_slot *pps;
-	struct bio_vec bio_vec;
-	struct bio bio;
+	__free_page(req->page);
+	kfree(req);
+}
+
+static void release_wb_ctl(struct zram_wb_ctl *wb_ctl)
+{
+	if (!wb_ctl)
+		return;
+
+	/* We should never have inflight requests at this point */
+	WARN_ON(atomic_read(&wb_ctl->num_inflight));
+	WARN_ON(!list_empty(&wb_ctl->done_reqs));
+
+	while (!list_empty(&wb_ctl->idle_reqs)) {
+		struct zram_wb_req *req;
+
+		req = list_first_entry(&wb_ctl->idle_reqs,
+				       struct zram_wb_req, entry);
+		list_del(&req->entry);
+		release_wb_req(req);
+	}
+
+	kfree(wb_ctl);
+}
+
+static struct zram_wb_ctl *init_wb_ctl(struct zram *zram)
+{
+	struct zram_wb_ctl *wb_ctl;
+	int i;
+
+	wb_ctl = kmalloc(sizeof(*wb_ctl), GFP_KERNEL);
+	if (!wb_ctl)
+		return NULL;
+
+	INIT_LIST_HEAD(&wb_ctl->idle_reqs);
+	INIT_LIST_HEAD(&wb_ctl->done_reqs);
+	atomic_set(&wb_ctl->num_inflight, 0);
+	init_waitqueue_head(&wb_ctl->done_wait);
+	spin_lock_init(&wb_ctl->done_lock);
+
+	for (i = 0; i < zram->wb_batch_size; i++) {
+		struct zram_wb_req *req;
+
+		/*
+		 * This is fatal condition only if we couldn't allocate
+		 * any requests at all.  Otherwise we just work with the
+		 * requests that we have successfully allocated, so that
+		 * writeback can still proceed, even if there is only one
+		 * request on the idle list.
+		 */
+		req = kzalloc(sizeof(*req), GFP_KERNEL | __GFP_NOWARN);
+		if (!req)
+			break;
+
+		req->page = alloc_page(GFP_KERNEL | __GFP_NOWARN);
+		if (!req->page) {
+			kfree(req);
+			break;
+		}
+
+		list_add(&req->entry, &wb_ctl->idle_reqs);
+	}
+
+	/* We couldn't allocate any requests, so writeabck is not possible */
+	if (list_empty(&wb_ctl->idle_reqs))
+		goto release_wb_ctl;
+
+	return wb_ctl;
+
+release_wb_ctl:
+	release_wb_ctl(wb_ctl);
+	return NULL;
+}
+
+static void zram_account_writeback_rollback(struct zram *zram)
+{
+	lockdep_assert_held_read(&zram->init_lock);
+
+	if (zram->wb_limit_enable)
+		zram->bd_wb_limit +=  1UL << (PAGE_SHIFT - 12);
+}
+
+static void zram_account_writeback_submit(struct zram *zram)
+{
+	lockdep_assert_held_read(&zram->init_lock);
+
+	if (zram->wb_limit_enable && zram->bd_wb_limit > 0)
+		zram->bd_wb_limit -=  1UL << (PAGE_SHIFT - 12);
+}
+
+static int zram_writeback_complete(struct zram *zram, struct zram_wb_req *req)
+{
+	u32 index = req->pps->index;
+	int err;
+
+	err = blk_status_to_errno(req->bio.bi_status);
+	if (err) {
+		/*
+		 * Failed wb requests should not be accounted in wb_limit
+		 * (if enabled).
+		 */
+		zram_account_writeback_rollback(zram);
+		zram_release_bdev_block(zram, req->blk_idx);
+		return err;
+	}
+
+	atomic64_inc(&zram->stats.bd_writes);
+	zram_slot_lock(zram, index);
+	/*
+	 * We release slot lock during writeback so slot can change under us:
+	 * slot_free() or slot_free() and zram_write_page(). In both cases
+	 * slot loses ZRAM_PP_SLOT flag. No concurrent post-processing can
+	 * set ZRAM_PP_SLOT on such slots until current post-processing
+	 * finishes.
+	 */
+	if (!zram_test_flag(zram, index, ZRAM_PP_SLOT)) {
+		zram_release_bdev_block(zram, req->blk_idx);
+		goto out;
+	}
+
+	zram_free_page(zram, index);
+	zram_set_flag(zram, index, ZRAM_WB);
+	zram_set_handle(zram, index, req->blk_idx);
+	atomic64_inc(&zram->stats.pages_stored);
+
+out:
+	zram_slot_unlock(zram, index);
+	return 0;
+}
+
+static void zram_writeback_endio(struct bio *bio)
+{
+	struct zram_wb_req *req = container_of(bio, struct zram_wb_req, bio);
+	struct zram_wb_ctl *wb_ctl = bio->bi_private;
+	unsigned long flags;
+
+	spin_lock_irqsave(&wb_ctl->done_lock, flags);
+	list_add(&req->entry, &wb_ctl->done_reqs);
+	spin_unlock_irqrestore(&wb_ctl->done_lock, flags);
+
+	wake_up(&wb_ctl->done_wait);
+}
+
+static void zram_submit_wb_request(struct zram *zram,
+				   struct zram_wb_ctl *wb_ctl,
+				   struct zram_wb_req *req)
+{
+	/*
+	 * wb_limit (if enabled) should be adjusted before submission,
+	 * so that we don't over-submit.
+	 */
+	zram_account_writeback_submit(zram);
+	atomic_inc(&wb_ctl->num_inflight);
+	req->bio.bi_private = wb_ctl;
+	submit_bio(&req->bio);
+}
+
+static int zram_complete_done_reqs(struct zram *zram,
+				   struct zram_wb_ctl *wb_ctl)
+{
+	struct zram_wb_req *req;
+	unsigned long flags;
 	int ret = 0, err;
-	u32 index;
 
-	page = alloc_page(GFP_KERNEL);
-	if (!page)
-		return -ENOMEM;
+	while (atomic_read(&wb_ctl->num_inflight) > 0) {
+		spin_lock_irqsave(&wb_ctl->done_lock, flags);
+		req = list_first_entry_or_null(&wb_ctl->done_reqs,
+					       struct zram_wb_req, entry);
+		if (req)
+			list_del(&req->entry);
+		spin_unlock_irqrestore(&wb_ctl->done_lock, flags);
+
+		/* ->num_inflight > 0 doesn't mean we have done requests */
+		if (!req)
+			break;
+
+		err = zram_writeback_complete(zram, req);
+		if (err)
+			ret = err;
+
+		atomic_dec(&wb_ctl->num_inflight);
+		release_pp_slot(zram, req->pps);
+		req->pps = NULL;
+
+		list_add(&req->entry, &wb_ctl->idle_reqs);
+	}
+
+	return ret;
+}
+
+static struct zram_wb_req *zram_select_idle_req(struct zram_wb_ctl *wb_ctl)
+{
+	struct zram_wb_req *req;
+
+	req = list_first_entry_or_null(&wb_ctl->idle_reqs,
+				       struct zram_wb_req, entry);
+	if (req)
+		list_del(&req->entry);
+	return req;
+}
+
+static int zram_writeback_slots(struct zram *zram,
+				struct zram_pp_ctl *ctl,
+				struct zram_wb_ctl *wb_ctl)
+{
+	unsigned long blk_idx = INVALID_BDEV_BLOCK;
+	struct zram_wb_req *req = NULL;
+	struct zram_pp_slot *pps;
+	int ret = 0, err = 0;
+	u32 index = 0;
 
 	while ((pps = select_pp_slot(ctl))) {
-		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);
-			if (!blk_idx) {
+		while (!req) {
+			req = zram_select_idle_req(wb_ctl);
+			if (req)
+				break;
+
+			wait_event(wb_ctl->done_wait,
+				   !list_empty(&wb_ctl->done_reqs));
+
+			err = zram_complete_done_reqs(zram, wb_ctl);
+			/*
+			 * BIO errors are not fatal, we continue and simply
+			 * attempt to writeback the remaining objects (pages).
+			 * At the same time we need to signal user-space that
+			 * some writes (at least one, but also could be all of
+			 * them) were not successful and we do so by returning
+			 * the most recent BIO error.
+			 */
+			if (err)
+				ret = err;
+		}
+
+		if (blk_idx == INVALID_BDEV_BLOCK) {
+			blk_idx = zram_reserve_bdev_block(zram);
+			if (blk_idx == INVALID_BDEV_BLOCK) {
 				ret = -ENOSPC;
 				break;
 			}
@@ -768,74 +1043,54 @@ static int zram_writeback_slots(struct zram *zram, struct zram_pp_ctl *ctl)
 		index = pps->index;
 		zram_slot_lock(zram, index);
 		/*
-		 * scan_slots() sets ZRAM_PP_SLOT and relases slot lock, so
+		 * scan_slots() sets ZRAM_PP_SLOT and releases slot lock, so
 		 * slots can change in the meantime. If slots are accessed or
 		 * freed they lose ZRAM_PP_SLOT flag and hence we don't
 		 * post-process them.
 		 */
 		if (!zram_test_flag(zram, index, ZRAM_PP_SLOT))
 			goto next;
-		if (zram_read_from_zspool(zram, page, index))
+		if (zram_read_from_zspool(zram, req->page, index))
 			goto next;
 		zram_slot_unlock(zram, index);
 
-		bio_init(&bio, zram->bdev, &bio_vec, 1,
-			 REQ_OP_WRITE | REQ_SYNC);
-		bio.bi_iter.bi_sector = blk_idx * (PAGE_SIZE >> 9);
-		__bio_add_page(&bio, page, PAGE_SIZE, 0);
-
-		/*
-		 * XXX: A single page IO would be inefficient for write
-		 * but it would be not bad as starter.
-		 */
-		err = submit_bio_wait(&bio);
-		if (err) {
-			release_pp_slot(zram, pps);
-			/*
-			 * BIO errors are not fatal, we continue and simply
-			 * attempt to writeback the remaining objects (pages).
-			 * At the same time we need to signal user-space that
-			 * some writes (at least one, but also could be all of
-			 * them) were not successful and we do so by returning
-			 * the most recent BIO error.
-			 */
-			ret = err;
-			continue;
-		}
-
-		atomic64_inc(&zram->stats.bd_writes);
-		zram_slot_lock(zram, index);
 		/*
-		 * Same as above, we release slot lock during writeback so
-		 * slot can change under us: slot_free() or slot_free() and
-		 * reallocation (zram_write_page()). In both cases slot loses
-		 * ZRAM_PP_SLOT flag. No concurrent post-processing can set
-		 * ZRAM_PP_SLOT on such slots until current post-processing
-		 * finishes.
+		 * From now on pp-slot is owned by the req, remove it from
+		 * its pp bucket.
 		 */
-		if (!zram_test_flag(zram, index, ZRAM_PP_SLOT))
-			goto next;
+		list_del_init(&pps->entry);
+
+		req->blk_idx = blk_idx;
+		req->pps = pps;
+		bio_init(&req->bio, zram->bdev, &req->bio_vec, 1, REQ_OP_WRITE);
+		req->bio.bi_iter.bi_sector = req->blk_idx * (PAGE_SIZE >> 9);
+		req->bio.bi_end_io = zram_writeback_endio;
+		__bio_add_page(&req->bio, req->page, PAGE_SIZE, 0);
+
+		zram_submit_wb_request(zram, wb_ctl, req);
+		blk_idx = INVALID_BDEV_BLOCK;
+		req = NULL;
+		cond_resched();
+		continue;
 
-		zram_free_page(zram, index);
-		zram_set_flag(zram, index, ZRAM_WB);
-		zram_set_handle(zram, index, blk_idx);
-		blk_idx = 0;
-		atomic64_inc(&zram->stats.pages_stored);
-		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);
 		release_pp_slot(zram, pps);
-
-		cond_resched();
 	}
 
-	if (blk_idx)
-		free_block_bdev(zram, blk_idx);
-	if (page)
-		__free_page(page);
+	/*
+	 * Selected idle req, but never submitted it due to some error or
+	 * wb limit.
+	 */
+	if (req)
+		release_wb_req(req);
+
+	while (atomic_read(&wb_ctl->num_inflight) > 0) {
+		wait_event(wb_ctl->done_wait, !list_empty(&wb_ctl->done_reqs));
+		err = zram_complete_done_reqs(zram, wb_ctl);
+		if (err)
+			ret = err;
+	}
 
 	return ret;
 }
@@ -948,7 +1203,8 @@ static ssize_t writeback_store(struct device *dev,
 	struct zram *zram = dev_to_zram(dev);
 	u64 nr_pages = zram->disksize >> PAGE_SHIFT;
 	unsigned long lo = 0, hi = nr_pages;
-	struct zram_pp_ctl *ctl = NULL;
+	struct zram_pp_ctl *pp_ctl = NULL;
+	struct zram_wb_ctl *wb_ctl = NULL;
 	char *args, *param, *val;
 	ssize_t ret = len;
 	int err, mode = 0;
@@ -970,8 +1226,14 @@ static ssize_t writeback_store(struct device *dev,
 		goto release_init_lock;
 	}
 
-	ctl = init_pp_ctl();
-	if (!ctl) {
+	pp_ctl = init_pp_ctl();
+	if (!pp_ctl) {
+		ret = -ENOMEM;
+		goto release_init_lock;
+	}
+
+	wb_ctl = init_wb_ctl(zram);
+	if (!wb_ctl) {
 		ret = -ENOMEM;
 		goto release_init_lock;
 	}
@@ -1000,7 +1262,7 @@ static ssize_t writeback_store(struct device *dev,
 				goto release_init_lock;
 			}
 
-			scan_slots_for_writeback(zram, mode, lo, hi, ctl);
+			scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
 			break;
 		}
 
@@ -1011,7 +1273,7 @@ static ssize_t writeback_store(struct device *dev,
 				goto release_init_lock;
 			}
 
-			scan_slots_for_writeback(zram, mode, lo, hi, ctl);
+			scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
 			break;
 		}
 
@@ -1022,7 +1284,7 @@ static ssize_t writeback_store(struct device *dev,
 				goto release_init_lock;
 			}
 
-			scan_slots_for_writeback(zram, mode, lo, hi, ctl);
+			scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
 			continue;
 		}
 
@@ -1033,17 +1295,18 @@ static ssize_t writeback_store(struct device *dev,
 				goto release_init_lock;
 			}
 
-			scan_slots_for_writeback(zram, mode, lo, hi, ctl);
+			scan_slots_for_writeback(zram, mode, lo, hi, pp_ctl);
 			continue;
 		}
 	}
 
-	err = zram_writeback_slots(zram, ctl);
+	err = zram_writeback_slots(zram, pp_ctl, wb_ctl);
 	if (err)
 		ret = err;
 
 release_init_lock:
-	release_pp_ctl(zram, ctl);
+	release_pp_ctl(zram, pp_ctl);
+	release_wb_ctl(wb_ctl);
 	atomic_set(&zram->pp_in_progress, 0);
 	up_read(&zram->init_lock);
 
@@ -1112,7 +1375,9 @@ static int read_from_bdev(struct zram *zram, struct page *page,
 	return -EIO;
 }
 
-static void free_block_bdev(struct zram *zram, unsigned long blk_idx) {};
+static void zram_release_bdev_block(struct zram *zram, unsigned long blk_idx)
+{
+}
 #endif
 
 #ifdef CONFIG_ZRAM_MEMORY_TRACKING
@@ -1634,7 +1899,7 @@ static void zram_free_page(struct zram *zram, size_t index)
 
 	if (zram_test_flag(zram, index, ZRAM_WB)) {
 		zram_clear_flag(zram, index, ZRAM_WB);
-		free_block_bdev(zram, zram_get_handle(zram, index));
+		zram_release_bdev_block(zram, zram_get_handle(zram, index));
 		goto out;
 	}
 
@@ -1740,14 +2005,14 @@ static int zram_read_page(struct zram *zram, struct page *page, u32 index,
 		ret = zram_read_from_zspool(zram, page, index);
 		zram_slot_unlock(zram, index);
 	} else {
+		unsigned long blk_idx = zram_get_handle(zram, index);
+
 		/*
 		 * The slot should be unlocked before reading from the backing
 		 * device.
 		 */
 		zram_slot_unlock(zram, index);
-
-		ret = read_from_bdev(zram, page, zram_get_handle(zram, index),
-				     parent);
+		ret = read_from_bdev(zram, page, blk_idx, parent);
 	}
 
 	/* Should NEVER happen. Return bio error if it does. */
@@ -2610,6 +2875,7 @@ static DEVICE_ATTR_RW(backing_dev);
 static DEVICE_ATTR_WO(writeback);
 static DEVICE_ATTR_RW(writeback_limit);
 static DEVICE_ATTR_RW(writeback_limit_enable);
+static DEVICE_ATTR_RW(writeback_batch_size);
 #endif
 #ifdef CONFIG_ZRAM_MULTI_COMP
 static DEVICE_ATTR_RW(recomp_algorithm);
@@ -2631,6 +2897,7 @@ static struct attribute *zram_disk_attrs[] = {
 	&dev_attr_writeback.attr,
 	&dev_attr_writeback_limit.attr,
 	&dev_attr_writeback_limit_enable.attr,
+	&dev_attr_writeback_batch_size.attr,
 #endif
 	&dev_attr_io_stat.attr,
 	&dev_attr_mm_stat.attr,
@@ -2692,7 +2959,7 @@ static int zram_add(void)
 
 	init_rwsem(&zram->init_lock);
 #ifdef CONFIG_ZRAM_WRITEBACK
-	spin_lock_init(&zram->wb_limit_lock);
+	zram->wb_batch_size = 32;
 #endif
 
 	/* gendisk structure */
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 6cee93f9c0d0..c6d94501376c 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -127,8 +127,8 @@ struct zram {
 	bool claim; /* Protected by disk->open_mutex */
 #ifdef CONFIG_ZRAM_WRITEBACK
 	struct file *backing_dev;
-	spinlock_t wb_limit_lock;
 	bool wb_limit_enable;
+	u32 wb_batch_size;
 	u64 bd_wb_limit;
 	struct block_device *bdev;
 	unsigned long *bitmap;