[PATCH] bcache: don't allocate full_dirty_stripes and stripe_sectors_dirty for flash device

[Coly Li <colyli@suse.de>]

The flash device is a special bcache device which doesn't have backing
device and stores all data on cache set. Although its data is treated
as dirty data but the writeback to backing device never happens.

Therefore it is unncessary to always allocate memory for counters
full_dirty_stripes and stripe_sectors_dirty when the bcache device is
on flash only.

This patch avoids to allocate/free memory for full_dirty_stripes and
stripe_sectors_dirty in bcache_device_init() and bcache_device_free().
Also in bcache_dev_sectors_dirty_add(), if the data is written onto
flash device, avoid to update the counters in full_dirty_stripes and
stripe_sectors_dirty because they are not used at all.

Signed-off-by: Coly Li <colyli@suse.de>
Cc: Mingzhe Zou <mingzhe.zou@easystack.cn>
---
 drivers/md/bcache/super.c     | 18 ++++++++++++++----
 drivers/md/bcache/writeback.c |  8 +++++++-
 2 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 077149c4050b..00edc093e544 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -887,12 +887,15 @@ static void bcache_device_free(struct bcache_device *d)
 	}
 
 	bioset_exit(&d->bio_split);
-	kvfree(d->full_dirty_stripes);
-	kvfree(d->stripe_sectors_dirty);
+	if (d->full_dirty_stripes)
+		kvfree(d->full_dirty_stripes);
+	if (d->stripe_sectors_dirty)
+		kvfree(d->stripe_sectors_dirty);
 
 	closure_debug_destroy(&d->cl);
 }
 
+
 static int bcache_device_init(struct bcache_device *d, unsigned int block_size,
 		sector_t sectors, struct block_device *cached_bdev,
 		const struct block_device_operations *ops)
@@ -914,6 +917,10 @@ static int bcache_device_init(struct bcache_device *d, unsigned int block_size,
 	}
 	d->nr_stripes = n;
 
+	/* Skip allocating stripes counters for flash device */
+	if (d->c && UUID_FLASH_ONLY(&d->c->uuids[d->id]))
+		goto get_idx;
+
 	n = d->nr_stripes * sizeof(atomic_t);
 	d->stripe_sectors_dirty = kvzalloc(n, GFP_KERNEL);
 	if (!d->stripe_sectors_dirty)
@@ -924,6 +931,7 @@ static int bcache_device_init(struct bcache_device *d, unsigned int block_size,
 	if (!d->full_dirty_stripes)
 		goto out_free_stripe_sectors_dirty;
 
+get_idx:
 	idx = ida_simple_get(&bcache_device_idx, 0,
 				BCACHE_DEVICE_IDX_MAX, GFP_KERNEL);
 	if (idx < 0)
@@ -981,9 +989,11 @@ static int bcache_device_init(struct bcache_device *d, unsigned int block_size,
 out_ida_remove:
 	ida_simple_remove(&bcache_device_idx, idx);
 out_free_full_dirty_stripes:
-	kvfree(d->full_dirty_stripes);
+	if (d->full_dirty_stripes)
+		kvfree(d->full_dirty_stripes);
 out_free_stripe_sectors_dirty:
-	kvfree(d->stripe_sectors_dirty);
+	if (d->stripe_sectors_dirty)
+		kvfree(d->stripe_sectors_dirty);
 	return -ENOMEM;
 
 }
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
index 24c049067f61..32a034e74622 100644
--- a/drivers/md/bcache/writeback.c
+++ b/drivers/md/bcache/writeback.c
@@ -607,8 +607,14 @@ void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned int inode,
 	if (stripe < 0)
 		return;
 
-	if (UUID_FLASH_ONLY(&c->uuids[inode]))
+	/*
+	 * The flash device doesn't have backing device to writeback,
+	 * it is unncessary to calculate stripes related stuffs.
+	 */
+	if (UUID_FLASH_ONLY(&c->uuids[inode])) {
 		atomic_long_add(nr_sectors, &c->flash_dev_dirty_sectors);
+		return;
+	}
 
 	stripe_offset = offset & (d->stripe_size - 1);
 
-- 
2.35.3