Date:   Mon, 17 Sep 2018 18:27:01 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <yuchao0@...wei.com>
Subject: Re: [PATCH] f2fs: allow out-place-update for direct IO in LFS mode

On 09/16, Chao Yu wrote:
> From: Chao Yu <yuchao0@...wei.com>
> 
> Normally, DIO uses in-pllace-update, but in LFS mode, f2fs doesn't
> allow triggering any in-place-update writes, so we fallback direct
> write to buffered write, result in bad performance of large size
> write.

I remember this is to serialize all the IOs in one buffered IO path to keep
the IO sequence espeicially useful for SMR drivers. Could you confirm whether
there is any IO reordering problem?

> 
> This patch adds to support triggering out-place-update for direct IO
> to enhance its performance.
> 
> Note that it needs to exclude direct read IO during direct write,
> since new data writing to new block address will no be valid until
> write finished.
> 
> storage: zram
> 
> time xfs_io -f -d /mnt/f2fs/file -c "pwrite 0 1073741824" -c "fsync"
> 
> Before:
> real	0m13.061s
> user	0m0.327s
> sys	0m12.486s
> 
> After:
> real	0m6.448s
> user	0m0.228s
> sys	0m6.212s
> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/data.c | 41 +++++++++++++++++++++++++++++++++--------
>  fs/f2fs/f2fs.h | 39 +++++++++++++++++++++++++++++++++++----
>  fs/f2fs/file.c |  3 ++-
>  3 files changed, 70 insertions(+), 13 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 048f9cf1d589..9937dc2f384a 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -894,7 +894,7 @@ static int __allocate_data_block(struct dnode_of_data *dn, int seg_type)
>  
>  	dn->data_blkaddr = datablock_addr(dn->inode,
>  				dn->node_page, dn->ofs_in_node);
> -	if (dn->data_blkaddr == NEW_ADDR)
> +	if (dn->data_blkaddr != NULL_ADDR)
>  		goto alloc;
>  
>  	if (unlikely((err = inc_valid_block_count(sbi, dn->inode, &count))))
> @@ -950,7 +950,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
>  
>  	if (direct_io) {
>  		map.m_seg_type = f2fs_rw_hint_to_seg_type(iocb->ki_hint);
> -		flag = f2fs_force_buffered_io(inode, WRITE) ?
> +		flag = f2fs_force_buffered_io(inode, iocb, from) ?
>  					F2FS_GET_BLOCK_PRE_AIO :
>  					F2FS_GET_BLOCK_PRE_DIO;
>  		goto map_blocks;
> @@ -1069,7 +1069,15 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map,
>  		goto sync_out;
>  	}
>  
> -	if (!is_valid_data_blkaddr(sbi, blkaddr)) {
> +	if (is_valid_data_blkaddr(sbi, blkaddr)) {
> +		/* use out-place-update for driect IO under LFS mode */
> +		if (test_opt(sbi, LFS) && create &&
> +				flag == F2FS_GET_BLOCK_DEFAULT) {
> +			err = __allocate_data_block(&dn, map->m_seg_type);
> +			if (!err)
> +				set_inode_flag(inode, FI_APPEND_WRITE);
> +		}
> +	} else {
>  		if (create) {
>  			if (unlikely(f2fs_cp_error(sbi))) {
>  				err = -EIO;
> @@ -2491,36 +2499,53 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>  	struct address_space *mapping = iocb->ki_filp->f_mapping;
>  	struct inode *inode = mapping->host;
>  	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> +	struct f2fs_inode_info *fi = F2FS_I(inode);
>  	size_t count = iov_iter_count(iter);
>  	loff_t offset = iocb->ki_pos;
>  	int rw = iov_iter_rw(iter);
>  	int err;
>  	enum rw_hint hint = iocb->ki_hint;
>  	int whint_mode = F2FS_OPTION(sbi).whint_mode;
> +	bool lock_read;
>  
>  	err = check_direct_IO(inode, iter, offset);
>  	if (err)
>  		return err < 0 ? err : 0;
>  
> -	if (f2fs_force_buffered_io(inode, rw))
> +	if (f2fs_force_buffered_io(inode, iocb, iter))
>  		return 0;
>  
> +	lock_read = allow_outplace_dio(inode, iocb, iter);
> +
>  	trace_f2fs_direct_IO_enter(inode, offset, count, rw);
>  
>  	if (rw == WRITE && whint_mode == WHINT_MODE_OFF)
>  		iocb->ki_hint = WRITE_LIFE_NOT_SET;
>  
> -	if (!down_read_trylock(&F2FS_I(inode)->i_gc_rwsem[rw])) {
> -		if (iocb->ki_flags & IOCB_NOWAIT) {
> +	if (iocb->ki_flags & IOCB_NOWAIT) {
> +		if (!down_read_trylock(&fi->i_gc_rwsem[rw])) {
> +			iocb->ki_hint = hint;
> +			err = -EAGAIN;
> +			goto out;
> +		}
> +		if (lock_read && !down_read_trylock(&fi->i_gc_rwsem[READ])) {
> +			up_read(&fi->i_gc_rwsem[rw]);
>  			iocb->ki_hint = hint;
>  			err = -EAGAIN;
>  			goto out;
>  		}
> -		down_read(&F2FS_I(inode)->i_gc_rwsem[rw]);
> +	} else {
> +		down_read(&fi->i_gc_rwsem[rw]);
> +		if (lock_read)
> +			down_read(&fi->i_gc_rwsem[READ]);
>  	}
>  
>  	err = blockdev_direct_IO(iocb, inode, iter, get_data_block_dio);
> -	up_read(&F2FS_I(inode)->i_gc_rwsem[rw]);
> +
> +	if (lock_read)
> +		up_read(&fi->i_gc_rwsem[READ]);
> +
> +	up_read(&fi->i_gc_rwsem[rw]);
>  
>  	if (rw == WRITE) {
>  		if (whint_mode == WHINT_MODE_OFF)
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 6f59ad180be7..a6dc9d581ee4 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -8,6 +8,7 @@
>  #ifndef _LINUX_F2FS_H
>  #define _LINUX_F2FS_H
>  
> +#include <linux/uio.h>
>  #include <linux/types.h>
>  #include <linux/page-flags.h>
>  #include <linux/buffer_head.h>
> @@ -3461,11 +3462,41 @@ static inline bool f2fs_may_encrypt(struct inode *inode)
>  #endif
>  }
>  
> -static inline bool f2fs_force_buffered_io(struct inode *inode, int rw)
> +static inline int block_unaligned_IO(struct inode *inode,
> +				struct kiocb *iocb, struct iov_iter *iter)
>  {
> -	return (f2fs_post_read_required(inode) ||
> -			(rw == WRITE && test_opt(F2FS_I_SB(inode), LFS)) ||
> -			F2FS_I_SB(inode)->s_ndevs);
> +	unsigned int i_blkbits = READ_ONCE(inode->i_blkbits);
> +	unsigned int blocksize_mask = (1 << i_blkbits) - 1;
> +	loff_t offset = iocb->ki_pos;
> +	unsigned long align = offset | iov_iter_alignment(iter);
> +
> +	return align & blocksize_mask;
> +}
> +
> +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));
> +}
> +
> +static inline bool f2fs_force_buffered_io(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);
> +
> +	if (f2fs_post_read_required(inode))
> +		return true;
> +	if (sbi->s_ndevs)
> +		return true;
> +	if (test_opt(sbi, LFS) && (rw == WRITE) &&
> +				block_unaligned_IO(inode, iocb, iter))
> +		return true;
> +	return false;
>  }
>  
>  #ifdef CONFIG_F2FS_FAULT_INJECTION
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 428e7398bd89..70491631e040 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -3018,7 +3018,8 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
>  				if (!f2fs_overwrite_io(inode, iocb->ki_pos,
>  						iov_iter_count(from)) ||
>  					f2fs_has_inline_data(inode) ||
> -					f2fs_force_buffered_io(inode, WRITE)) {
> +					f2fs_force_buffered_io(inode,
> +							iocb, from)) {
>  						clear_inode_flag(inode,
>  								FI_NO_PREALLOC);
>  						inode_unlock(inode);
> -- 
> 2.18.0

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