[PATCH v2] fs: don't flush pagecache when expanding block device

From: shunki-fujita
Date: Mon Mar 19 2018 - 07:01:06 EST


When changing the size of a block device, its all caches are freed.
It's necessary on shrinking to prevent spurious I/Os to the disappeared region.
However, on expanding, such kind of I/Os doesn't happen.

Similar things can be considered for btrfs filesystem resize and resize2fs,
but they are designed not to cache drops when expanding.
Therefore this patch removes unnecessary cache drop.

Signed-off-by: Shunki Fujita <shunki-fujita@xxxxxxxxxxxx>
---
Changes in v2:
- Remove unnecessary changes (Since bdev-> bd_invalidated always 0 after check_disk_size_change ()[1])
- Add document of check_disk_size_change ()

[1] https://github.com/torvalds/linux/blob/master/fs/block_dev.c#L1365-L1366

fs/block_dev.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index fe09ef9..63f1269 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1324,7 +1324,8 @@ static void flush_disk(struct block_device *bdev, bool kill_dirty)
* @bdev: struct bdev to adjust.
*
* This routine checks to see if the bdev size does not match the disk size
- * and adjusts it if it differs.
+ * and adjusts it if it differs. When shrinking the bdev size, its all caches
+ * are freed.
*/
void check_disk_size_change(struct gendisk *disk, struct block_device *bdev)
{
@@ -1337,7 +1338,8 @@ void check_disk_size_change(struct gendisk *disk, struct block_device *bdev)
"%s: detected capacity change from %lld to %lld\n",
disk->disk_name, bdev_size, disk_size);
i_size_write(bdev->bd_inode, disk_size);
- flush_disk(bdev, false);
+ if (bdev_size > disk_size)
+ flush_disk(bdev, false);
}
}
EXPORT_SYMBOL(check_disk_size_change);
--
2.7.4