Date:   Mon, 23 Jul 2018 21:47:47 +0900
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 v2] f2fs: split discard command in prior to block layer

On 07/15, Chao Yu wrote:
> On 2018/7/15 11:13, Jaegeuk Kim wrote:
> > On 07/15, Chao Yu wrote:
> >> Hi Jaegeuk,
> >>
> >> On 2018/7/15 9:27, Jaegeuk Kim wrote:
> >>> On 07/08, Chao Yu wrote:
> >>>> From: Chao Yu <yuchao0@...wei.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?
> >>
> >> Yep, could you check __submit_discard_cmd() implementation below? Does that
> >> match the thoughts from you?
> >>
> >> Thanks,
> >>
> >>>
> >>>>
> >>>> Signed-off-by: Chao Yu <yuchao0@...wei.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,
> >>>>  	}
> >>>>  }
> >>>>  
> >>>> -
> > 
> > ===================== BEGIN
> > 
> >>>> +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);
> > 
> > Keep the original one, since it's partially failed?
> 
> During __submit_discard_cmd(), we are trying to split original dc into multiple
> dc, and once we failed to submit some of them, we will remove corresponding dc,
> the removal logic is the same as before, not being changed...
> 
> If we want to keep failed dc and do retry, we'd better add another patch for
> that, right?

I thought removing failed portion of the dc.

> 
> > 
> >>>> +			return;
> >>>> +		}
> >>>> +		lstart += len;
> >>>> +		start += len;
> >>>> +		total_len -= len;
> >>>> +		len = total_len;
> >>>> +		(*issued)++;
> >>>> +
> >>>> +		if (len) {
> >>>> +			__update_discard_tree_range(sbi, bdev, lstart,
> >>>> +								start, len);
> > 
> > Do we really need this? We already grabbed one candidate which was not merged
> > well.
> 
> You mean submitting multiple bios based on one large size dc?

Yes.

> 
> Previously, one bio references to one dc as below, in end_io, it will change
> dc->state which can be detected by its own waiter.
> 
> 	bio->bi_private = dc;
> 	bio->bi_end_io = f2fs_submit_discard_endio;
> 	bio->bi_opf |= flag;
> 
> If multiple bios reference to one dc, it will be more complicated to handle
> that. How do you think?

I was concerned about too many entries in the lists. How about adding a refcnt
to count how many bios were issued on the dc?

Thanks,

> 
> Thanks,
> 
> > 
> >>>> +			dc = (struct discard_cmd *)f2fs_lookup_rb_tree(
> >>>> +						&dcc->root, NULL, lstart);
> >>>> +			f2fs_bug_on(sbi, !dc);
> >>>>  		}
> >>>> -	} else {
> >>>> -		__remove_discard_cmd(sbi, dc);
> >>>>  	}
> >>>> +
> >>>> +	return;
> >>>>  }
> > 
> > ======================= END
> > 
> > 
> >>>>  
> >>>>  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

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