[PATCH] ext4: disable mount with both dioread_nolock and nodelalloc

[Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>]

Mount with both dioread_nolock and nodelalloc will result in huge
performance drop, which indeed is an known issue, so before we fix
this issue, currently we disable this behaviour. Below test reproducer
can reveal this performance drop.

    mount -o remount,dioread_nolock,delalloc /dev/vdb1
    rm -f testfile
    start_time=$(date +%s)
    dd if=/dev/zero of=testfile bs=4096 count=$((1024*256))
    sync
    end_time=$(date +%s)
    echo $((end_time - start_time))

    mount -o remount,dioread_nolock,nodelalloc /dev/vdb1
    rm -f testfile
    start_time=$(date +%s)
    dd if=/dev/zero of=testfile bs=4096 count=$((1024*256))
    sync
    end_time=$(date +%s)
    echo $((end_time - start_time))

Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
---
 fs/ext4/super.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 4079605d437a..1a2b2c0cd1b8 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2098,6 +2098,12 @@ static int parse_options(char *options, struct super_block *sb,
 		int blocksize =
 			BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
 
+		if (!test_opt(sb, DELALLOC)) {
+			ext4_msg(sb, KERN_ERR, "can't mount with "
+				 "both dioread_nolock and nodelalloc");
+			return 0;
+		}
+
 		if (blocksize < PAGE_SIZE) {
 			ext4_msg(sb, KERN_ERR, "can't mount with "
 				 "dioread_nolock if block size != PAGE_SIZE");
-- 
2.17.2