Re: [PATCH v2] f2fs: split discard command in prior to block layer

[Jaegeuk Kim <jaegeuk@kernel.org>]

On 07/08, Chao Yu wrote:
> From: Chao Yu <yuchao0@huawei.com>
> 
> Some devices has small max_{hw,}discard_sectors, so that in
> __blkdev_issue_discard(), one big size discard bio can be split
> into multiple small size discard bios, result in heavy load in IO
> scheduler and device, which can hang other sync IO for long time.
> 
> Now, f2fs is trying to control discard commands more elaboratively,
> in order to make less conflict in between discard IO and user IO
> to enhance application's performance, so in this patch, we will
> split discard bio in f2fs in prior to in block layer to reduce
> issuing multiple discard bios in a short time.

Can we just change __submit_discard_cmd() to submit the large candidate
partially and adjust lstart in the original candidate?

> 
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> ---
> v2:
> - change to split discard command entry before submission.
>  fs/f2fs/f2fs.h    |  13 +++---
>  fs/f2fs/segment.c | 117 +++++++++++++++++++++++++++++++++++++-----------------
>  2 files changed, 86 insertions(+), 44 deletions(-)
> 
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index c48b655d5d8d..359526d88d3f 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -178,7 +178,6 @@ enum {
>  
>  #define MAX_DISCARD_BLOCKS(sbi)		BLKS_PER_SEC(sbi)
>  #define DEF_MAX_DISCARD_REQUEST		8	/* issue 8 discards per round */
> -#define DEF_MAX_DISCARD_LEN		512	/* Max. 2MB per discard */
>  #define DEF_MIN_DISCARD_ISSUE_TIME	50	/* 50 ms, if exists */
>  #define DEF_MID_DISCARD_ISSUE_TIME	500	/* 500 ms, if device busy */
>  #define DEF_MAX_DISCARD_ISSUE_TIME	60000	/* 60 s, if no candidates */
> @@ -709,22 +708,22 @@ static inline void set_extent_info(struct extent_info *ei, unsigned int fofs,
>  }
>  
>  static inline bool __is_discard_mergeable(struct discard_info *back,
> -						struct discard_info *front)
> +			struct discard_info *front, unsigned int max_len)
>  {
>  	return (back->lstart + back->len == front->lstart) &&
> -		(back->len + front->len < DEF_MAX_DISCARD_LEN);
> +		(back->len + front->len <= max_len);
>  }
>  
>  static inline bool __is_discard_back_mergeable(struct discard_info *cur,
> -						struct discard_info *back)
> +			struct discard_info *back, unsigned int max_len)
>  {
> -	return __is_discard_mergeable(back, cur);
> +	return __is_discard_mergeable(back, cur, max_len);
>  }
>  
>  static inline bool __is_discard_front_mergeable(struct discard_info *cur,
> -						struct discard_info *front)
> +			struct discard_info *front, unsigned int max_len)
>  {
> -	return __is_discard_mergeable(cur, front);
> +	return __is_discard_mergeable(cur, front, max_len);
>  }
>  
>  static inline bool __is_extent_mergeable(struct extent_info *back,
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index f7f56dd091b4..cbf8f3f9a8e7 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -966,17 +966,24 @@ static void __init_discard_policy(struct f2fs_sb_info *sbi,
>  	}
>  }
>  
> -
> +static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
> +				struct block_device *bdev, block_t lstart,
> +				block_t start, block_t len);
>  /* this function is copied from blkdev_issue_discard from block/blk-lib.c */
>  static void __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  						struct discard_policy *dpolicy,
> -						struct discard_cmd *dc)
> +						struct discard_cmd *dc,
> +						unsigned int *issued)
>  {
> +	struct block_device *bdev = dc->bdev;
> +	struct request_queue *q = bdev_get_queue(bdev);
> +	unsigned int max_discard_blocks =
> +			SECTOR_TO_BLOCK(q->limits.max_discard_sectors);
>  	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
>  	struct list_head *wait_list = (dpolicy->type == DPOLICY_FSTRIM) ?
>  					&(dcc->fstrim_list) : &(dcc->wait_list);
> -	struct bio *bio = NULL;
>  	int flag = dpolicy->sync ? REQ_SYNC : 0;
> +	block_t lstart, start, len, total_len;
>  
>  	if (dc->state != D_PREP)
>  		return;
> @@ -984,30 +991,63 @@ static void __submit_discard_cmd(struct f2fs_sb_info *sbi,
>  	if (is_sbi_flag_set(sbi, SBI_NEED_FSCK))
>  		return;
>  
> -	trace_f2fs_issue_discard(dc->bdev, dc->start, dc->len);
> -
> -	dc->error = __blkdev_issue_discard(dc->bdev,
> -				SECTOR_FROM_BLOCK(dc->start),
> -				SECTOR_FROM_BLOCK(dc->len),
> -				GFP_NOFS, 0, &bio);
> -	if (!dc->error) {
> -		/* should keep before submission to avoid D_DONE right away */
> -		dc->state = D_SUBMIT;
> -		atomic_inc(&dcc->issued_discard);
> -		atomic_inc(&dcc->issing_discard);
> -		if (bio) {
> -			bio->bi_private = dc;
> -			bio->bi_end_io = f2fs_submit_discard_endio;
> -			bio->bi_opf |= flag;
> -			submit_bio(bio);
> -			list_move_tail(&dc->list, wait_list);
> -			__check_sit_bitmap(sbi, dc->start, dc->start + dc->len);
> -
> -			f2fs_update_iostat(sbi, FS_DISCARD, 1);
> +	trace_f2fs_issue_discard(bdev, dc->start, dc->len);
> +
> +	lstart = dc->lstart;
> +	start = dc->start;
> +	len = dc->len;
> +	total_len = len;
> +
> +	while (total_len && *issued < dpolicy->max_requests) {
> +		struct bio *bio = NULL;
> +
> +		if (len > max_discard_blocks)
> +			len = max_discard_blocks;
> +
> +		dc->error = __blkdev_issue_discard(bdev,
> +					SECTOR_FROM_BLOCK(start),
> +					SECTOR_FROM_BLOCK(len),
> +					GFP_NOFS, 0, &bio);
> +		if (!dc->error) {
> +			/*
> +			 * should keep before submission to avoid D_DONE
> +			 * right away
> +			 */
> +			dc->state = D_SUBMIT;
> +			dc->len = len;
> +			atomic_inc(&dcc->issued_discard);
> +			atomic_inc(&dcc->issing_discard);
> +			if (bio) {
> +				bio->bi_private = dc;
> +				bio->bi_end_io = f2fs_submit_discard_endio;
> +				bio->bi_opf |= flag;
> +				submit_bio(bio);
> +				list_move_tail(&dc->list, wait_list);
> +				__check_sit_bitmap(sbi, dc->start,
> +							dc->start + dc->len);
> +
> +				f2fs_update_iostat(sbi, FS_DISCARD, 1);
> +			}
> +		} else {
> +			__remove_discard_cmd(sbi, dc);
> +			return;
> +		}
> +		lstart += len;
> +		start += len;
> +		total_len -= len;
> +		len = total_len;
> +		(*issued)++;
> +
> +		if (len) {
> +			__update_discard_tree_range(sbi, bdev, lstart,
> +								start, len);
> +			dc = (struct discard_cmd *)f2fs_lookup_rb_tree(
> +						&dcc->root, NULL, lstart);
> +			f2fs_bug_on(sbi, !dc);
>  		}
> -	} else {
> -		__remove_discard_cmd(sbi, dc);
>  	}
> +
> +	return;
>  }
>  
>  static struct discard_cmd *__insert_discard_tree(struct f2fs_sb_info *sbi,
> @@ -1088,10 +1128,11 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
>  	struct discard_cmd *dc;
>  	struct discard_info di = {0};
>  	struct rb_node **insert_p = NULL, *insert_parent = NULL;
> +	struct request_queue *q = bdev_get_queue(bdev);
> +	unsigned int max_discard_blocks =
> +			SECTOR_TO_BLOCK(q->limits.max_discard_sectors);
>  	block_t end = lstart + len;
>  
> -	mutex_lock(&dcc->cmd_lock);
> -
>  	dc = (struct discard_cmd *)f2fs_lookup_rb_tree_ret(&dcc->root,
>  					NULL, lstart,
>  					(struct rb_entry **)&prev_dc,
> @@ -1131,7 +1172,8 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
>  
>  		if (prev_dc && prev_dc->state == D_PREP &&
>  			prev_dc->bdev == bdev &&
> -			__is_discard_back_mergeable(&di, &prev_dc->di)) {
> +			__is_discard_back_mergeable(&di, &prev_dc->di,
> +							max_discard_blocks)) {
>  			prev_dc->di.len += di.len;
>  			dcc->undiscard_blks += di.len;
>  			__relocate_discard_cmd(dcc, prev_dc);
> @@ -1142,7 +1184,8 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
>  
>  		if (next_dc && next_dc->state == D_PREP &&
>  			next_dc->bdev == bdev &&
> -			__is_discard_front_mergeable(&di, &next_dc->di)) {
> +			__is_discard_front_mergeable(&di, &next_dc->di,
> +							max_discard_blocks)) {
>  			next_dc->di.lstart = di.lstart;
>  			next_dc->di.len += di.len;
>  			next_dc->di.start = di.start;
> @@ -1165,8 +1208,6 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
>  		node = rb_next(&prev_dc->rb_node);
>  		next_dc = rb_entry_safe(node, struct discard_cmd, rb_node);
>  	}
> -
> -	mutex_unlock(&dcc->cmd_lock);
>  }
>  
>  static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
> @@ -1181,7 +1222,9 @@ static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
>  
>  		blkstart -= FDEV(devi).start_blk;
>  	}
> +	mutex_lock(&SM_I(sbi)->dcc_info->cmd_lock);
>  	__update_discard_tree_range(sbi, bdev, lblkstart, blkstart, blklen);
> +	mutex_unlock(&SM_I(sbi)->dcc_info->cmd_lock);
>  	return 0;
>  }
>  
> @@ -1220,9 +1263,9 @@ static unsigned int __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
>  		}
>  
>  		dcc->next_pos = dc->lstart + dc->len;
> -		__submit_discard_cmd(sbi, dpolicy, dc);
> +		__submit_discard_cmd(sbi, dpolicy, dc, &issued);
>  
> -		if (++issued >= dpolicy->max_requests)
> +		if (issued >= dpolicy->max_requests)
>  			break;
>  next:
>  		node = rb_next(&dc->rb_node);
> @@ -1277,9 +1320,9 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
>  				break;
>  			}
>  
> -			__submit_discard_cmd(sbi, dpolicy, dc);
> +			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
>  
> -			if (++issued >= dpolicy->max_requests)
> +			if (issued >= dpolicy->max_requests)
>  				break;
>  		}
>  		blk_finish_plug(&plug);
> @@ -2475,9 +2518,9 @@ static unsigned int __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
>  			goto skip;
>  		}
>  
> -		__submit_discard_cmd(sbi, dpolicy, dc);
> +		__submit_discard_cmd(sbi, dpolicy, dc, &issued);
>  
> -		if (++issued >= dpolicy->max_requests) {
> +		if (issued >= dpolicy->max_requests) {
>  			start = dc->lstart + dc->len;
>  
>  			blk_finish_plug(&plug);
> -- 
> 2.16.2.17.g38e79b1fd