linux-ext4 - Re: [PATCH] ext4: disable mount with both dioread

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Date:   Thu, 1 Aug 2019 09:57:12 +0800
From:   Joseph Qi <jiangqi903@...il.com>
To:     Xiaoguang Wang <xiaoguang.wang@...ux.alibaba.com>,
        linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: disable mount with both dioread_nolock and
 nodelalloc



On 19/7/31 21:06, Xiaoguang Wang wrote:
> 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@...ux.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;
> +		}
> +
I suggest move it down to keep blocksize check logic together.

Other than that, looks good to me.
Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>

>  		if (blocksize < PAGE_SIZE) {
>  			ext4_msg(sb, KERN_ERR, "can't mount with "
>  				 "dioread_nolock if block size != PAGE_SIZE");
>