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

[Jaegeuk Kim]

On 07/07, Chao Yu wrote:
> Hi Jaegeuk,
> 
> On 2018/7/7 6:45, Jaegeuk Kim wrote:
> > On 07/04, Chao Yu wrote:
> >> From: Chao Yu <yuchao0@xxxxxxxxxx>
> >>
> >> 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.
> > 
> > Hi Chao,
> > 
> > In terms of # of candidates, can we control this when actually issuing
> > the discard commands?
> 
> IIUC, you mean once we pick one discard entry in rbtree, if
> max_{hw,}discard_sectors is smaller than size of this discard, then we can split
> it into smaller ones by discard_sectors, and just issue one or partials of them?

Yes, sort of.

> 
> Thanks,
> 
> > 
> > Thanks,
> > 
> >>
> >> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> >> ---
> >>  fs/f2fs/f2fs.h    | 13 ++++++-------
> >>  fs/f2fs/segment.c | 25 ++++++++++++++++++++++---
> >>  2 files changed, 28 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >> index a9da5a089cb4..a09d2b2d9520 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 */
> >> @@ -701,22 +700,22 @@ 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 4648561e2bfd..8e417a12684d 100644
> >> --- a/fs/f2fs/segment.c
> >> +++ b/fs/f2fs/segment.c
> >> @@ -1086,6 +1086,9 @@ 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);
> >> @@ -1129,7 +1132,8 @@ 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);
> >> @@ -1140,7 +1144,8 @@ 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;
> >> @@ -1170,7 +1175,11 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
> >>  static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
> >>  		struct block_device *bdev, block_t blkstart, block_t blklen)
> >>  {
> >> +	struct request_queue *q = bdev_get_queue(bdev);
> >> +	unsigned int max_discard_blocks =
> >> +			SECTOR_TO_BLOCK(q->limits.max_discard_sectors);
> >>  	block_t lblkstart = blkstart;
> >> +	block_t total_len = blklen;
> >>  
> >>  	trace_f2fs_queue_discard(bdev, blkstart, blklen);
> >>  
> >> @@ -1179,7 +1188,17 @@ static int __queue_discard_cmd(struct f2fs_sb_info *sbi,
> >>  
> >>  		blkstart -= FDEV(devi).start_blk;
> >>  	}
> >> -	__update_discard_tree_range(sbi, bdev, lblkstart, blkstart, blklen);
> >> +
> >> +	while (total_len) {
> >> +		if (blklen > max_discard_blocks)
> >> +			blklen = max_discard_blocks;
> >> +		__update_discard_tree_range(sbi, bdev, lblkstart,
> >> +						blkstart, blklen);
> >> +		lblkstart += blklen;
> >> +		blkstart += blklen;
> >> +		total_len -= blklen;
> >> +		blklen = total_len;
> >> +	}
> >>  	return 0;
> >>  }
> >>  
> >> -- 
> >> 2.16.2.17.g38e79b1fd