RE: [f2fs-dev] [PATCH 3/4] f2fs: avoid f2fs_lock_op in f2fs_write_begin

[Chao Yu]

Hi Jaegeuk,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@xxxxxxxxxx]
> Sent: Thursday, December 24, 2015 10:15 AM
> To: linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx;
> linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: Jaegeuk Kim
> Subject: [f2fs-dev] [PATCH 3/4] f2fs: avoid f2fs_lock_op in f2fs_write_begin
> 
> If f2fs_write_begin is to update data, we can bypass calling f2fs_lock_op() in
> order to avoid the checkpoint latency in the write syscall.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> ---
>  fs/f2fs/data.c | 43 ++++++++++++++++++++++++++++++++++---------
>  1 file changed, 34 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 49092da..d53cf4f 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1418,10 +1418,16 @@ static int prepare_write_begin(struct f2fs_sb_info *sbi,
>  	pgoff_t index = page->index;
>  	struct dnode_of_data dn;
>  	struct page *ipage;
> +	bool locked = false;
> +	struct extent_info ei;
>  	int err = 0;
> 
> -	f2fs_lock_op(sbi);
> -
> +	if (f2fs_has_inline_data(inode) ||
> +			(pos & PAGE_CACHE_MASK) >= i_size_read(inode)) {
> +		f2fs_lock_op(sbi);
> +		locked = true;
> +	}
> +restart:
>  	/* check inline_data */
>  	ipage = get_node_page(sbi, inode->i_ino);
>  	if (IS_ERR(ipage)) {
> @@ -1436,22 +1442,41 @@ static int prepare_write_begin(struct f2fs_sb_info *sbi,
>  			read_inline_data(page, ipage);
>  			set_inode_flag(F2FS_I(inode), FI_DATA_EXIST);
>  			sync_inode_page(&dn);
> -			goto done;
>  		} else {
>  			err = f2fs_convert_inline_page(&dn, page);
>  			if (err)
> -				goto err_out;
> +				goto out;
> +			err = f2fs_get_block(&dn, index);

Seems after f2fs_convert_inline_page, data_blkaddr and node_changed should
have been set, so f2fs_get_block could be removed here.

> +		}
> +	} else if (locked) {
> +		err = f2fs_get_block(&dn, index);
> +	} else {
> +		if (f2fs_lookup_extent_cache(inode, index, &ei)) {
> +			dn.data_blkaddr = ei.blk + index - ei.fofs;
> +		} else {
> +			bool restart = false;
> +
> +			/* hole case */
> +			err = get_dnode_of_data(&dn, index, LOOKUP_NODE);

Better to handle error case like -ENOMEM or -EIO.

Thanks,

> +			if (err || (!err && dn.data_blkaddr == NULL_ADDR))
> +				restart = true;
> +			if (restart) {
> +				f2fs_put_dnode(&dn);
> +				f2fs_lock_op(sbi);
> +				locked = true;
> +				goto restart;
> +			}
>  		}
>  	}
> -	err = f2fs_get_block(&dn, index);
> -done:
> +
>  	/* convert_inline_page can make node_changed */
>  	*blk_addr = dn.data_blkaddr;
>  	*node_changed = dn.node_changed;
> -err_out:
> +out:
>  	f2fs_put_dnode(&dn);
>  unlock_out:
> -	f2fs_unlock_op(sbi);
> +	if (locked)
> +		f2fs_unlock_op(sbi);
>  	return err;
>  }
> 
> @@ -1488,7 +1513,7 @@ repeat:
> 
>  	*pagep = page;
> 
> -	err = prepare_write_begin(sbi, page, pos + len,
> +	err = prepare_write_begin(sbi, page, pos,  len,
>  					&blkaddr, &need_balance);
>  	if (err)
>  		goto fail;
> --
> 2.5.4 (Apple Git-61)
> 
> 
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