linux-kernel - [PATCH] fs: don't flush pagecache when expanding block device

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Date:   Fri, 16 Mar 2018 15:55:53 +0900
From:   shunki-fujita <shunki-fujita@...ozu.co.jp>
To:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        shunki-fujita@...ozu.co.jp
Subject: [PATCH] fs: don't flush pagecache when expanding block device

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@...ozu.co.jp>
---
 fs/block_dev.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index fe09ef9..243f4002 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1337,7 +1337,14 @@ 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);
+		} else {
+			if (!bdev->bd_disk)
+				return;
+			if (disk_part_scan_enabled(bdev->bd_disk))
+				bdev->bd_invalidated = 1;
+		}
 	}
 }
 EXPORT_SYMBOL(check_disk_size_change);
-- 
2.7.4