Re: [PATCH] f2fs: allow out-place-update for direct IO in LFS mode

[Jaegeuk Kim]

On 09/18, Chao Yu wrote:
> On 2018/9/18 9:27, Jaegeuk Kim wrote:
> > On 09/16, Chao Yu wrote:
> >> From: Chao Yu <yuchao0@xxxxxxxxxx>
> >>
> >> 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?
> 
> IMO, buffered IO will encounter reordering issue more easily, for example:
> 
> User write 2mb data via DIO, but according to policy on LFS mode, it will
> fallback to buffered IO.
> 
> Before dio triggers writeback, an async writeback from background is
> triggered, so all IO distribution can be:
> 
> 		page		LBA range
> async IO:	0 - 255		x + 0, x + 255
> sync IO:	256 - 511	x + 256, x + 511
> 
> Then block IO scheduler can issue sync IO before async IO, result IO
> reordering.
> 
> Anyway, in DIO path we will suffer less IO reordering issue.

My concern was on mixed DIO and buffered IOs where we don't have a way to
serialize all the IOs.

> 
> Thanks,
> 
> > 
> >>
> >> 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@xxxxxxxxxx>
> >> ---
> >>  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
> > 
> > .
> >