linux-kernel - Re: [PATCH] f2fs: disble physical prealloc in LSF mount

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Date:   Mon, 25 Nov 2019 00:48:37 +0000
From:   Damien Le Moal <Damien.LeMoal@....com>
To:     Javier González <javier@...igon.com>,
        "jaegeuk@...nel.org" <jaegeuk@...nel.org>,
        "yuchao0@...wei.com" <yuchao0@...wei.com>
CC:     "linux-f2fs-devel@...ts.sourceforge.net" 
        <linux-f2fs-devel@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Javier González <javier.gonz@...sung.com>
Subject: Re: [PATCH] f2fs: disble physical prealloc in LSF mount

On 2019/11/22 18:00, Javier González wrote:
> From: Javier González <javier.gonz@...sung.com>
> 
> Fix file system corruption when using LFS mount (e.g., in zoned
> devices). Seems like the fallback into buffered I/O creates an
> inconsistency if the application is assuming both read and write DIO. I
> can easily reproduce a corruption with a simple RocksDB test.
> 
> Might be that the f2fs_forced_buffered_io path brings some problems too,
> but I have not seen other failures besides this one.
> 
> Problem reproducible without a zoned block device, simply by forcing
> LFS mount:
> 
>   $ sudo mkfs.f2fs -f -m /dev/nvme0n1
>   $ sudo mount /dev/nvme0n1 /mnt/f2fs
>   $ sudo  /opt/rocksdb/db_bench  --benchmarks=fillseq --use_existing_db=0
>   --use_direct_reads=true --use_direct_io_for_flush_and_compaction=true
>   --db=/mnt/f2fs --num=5000 --value_size=1048576 --verify_checksum=1
>   --block_size=65536
> 
> Note that the options that cause the problem are:
>   --use_direct_reads=true --use_direct_io_for_flush_and_compaction=true
> 
> Fixes: f9d6d0597698 ("f2fs: fix out-place-update DIO write")
> 
> Signed-off-by: Javier González <javier.gonz@...sung.com>
> ---
>  fs/f2fs/data.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 5755e897a5f0..b045dd6ab632 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1081,9 +1081,6 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
>  			return err;
>  	}
>  
> -	if (direct_io && allow_outplace_dio(inode, iocb, from))
> -		return 0;

Since for LFS mode, all DIOs can end up out of place, I think that it
may be better to change allow_outplace_dio() to always return true in
the case of LFS mode. So may be something like:

static inline int allow_outplace_dio(struct inode *inode,
			struct kiocb *iocb, struct iov_iter *iter)
{
	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
	int rw = iov_iter_rw(iter);

	return test_opt(sbi, LFS) ||
	 	(rw == WRITE && !block_unaligned_IO(inode, iocb, iter));
}

instead of the original:

static inline int allow_outplace_dio(struct inode *inode,
			struct kiocb *iocb, struct iov_iter *iter)
{
	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
	int rw = iov_iter_rw(iter);

	return (test_opt(sbi, LFS) && (rw == WRITE) &&
				!block_unaligned_IO(inode, iocb, iter));
}

Thoughts ?

> -
>  	if (is_inode_flag_set(inode, FI_NO_PREALLOC))
>  		return 0;
>  
> 


-- 
Damien Le Moal
Western Digital Research