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

[Chao Yu <yuchao0@huawei.com>]

On 2018/9/19 0:27, Jaegeuk Kim wrote:
> 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@huawei.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?
>>
>> 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.

As I explained above, even we always use buffered IO, there is no such
guarantee for serializing all async/sync IO in block layer, am I missing
something?

If you really don't want to change the logic for SMR, how about let me just
leave that case?

Thanks,

> 
>>
>> 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@huawei.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
>>>
>>> .
>>>
> 
> .
>