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

[Chao Yu]

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.

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