f2fs: don't hold cmd_lock during waiting discard command

Previously, with protection of cmd_lock, we will wait for end io of discard command which potentially may lead long latency, making worse concurrency. So, in this patch, we try to add reference into discard entry to prevent the entry being released by other thread, then we can avoid holding global cmd_lock during waiting discard to finish. Signed-off-by: Chao Yu <[email protected]> Signed-off-by: Jaegeuk Kim <[email protected]>
modi0012 · May 3, 2017 · ec9895a · ec9895a
1 parent 4d97807
commit ec9895a
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Showing 2 changed files with 21 additions and 5 deletions.
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
@@ -219,6 +219,7 @@ struct discard_cmd {
 	struct list_head list;		/* command list */
 	struct completion wait;		/* compleation */
 	struct block_device *bdev;	/* bdev */
+	unsigned short ref;		/* reference count */
 	int state;			/* state */
 	int error;			/* bio error */
 };

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
@@ -688,6 +688,7 @@ static struct discard_cmd *__create_discard_cmd(struct f2fs_sb_info *sbi,
 	dc->lstart = lstart;
 	dc->start = start;
 	dc->len = len;
+	dc->ref = 0;
 	dc->state = D_PREP;
 	dc->error = 0;
 	init_completion(&dc->wait);
@@ -1007,6 +1008,8 @@ static void __wait_discard_cmd(struct f2fs_sb_info *sbi, bool wait_cond)
 	mutex_lock(&dcc->cmd_lock);
 	list_for_each_entry_safe(dc, tmp, wait_list, list) {
 		if (!wait_cond || dc->state == D_DONE) {
+			if (dc->ref)
+				continue;
 			wait_for_completion_io(&dc->wait);
 			__remove_discard_cmd(sbi, dc);
 		}
@@ -1019,17 +1022,29 @@ void f2fs_wait_discard_bio(struct f2fs_sb_info *sbi, block_t blkaddr)
 {
 	struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
 	struct discard_cmd *dc;
+	bool need_wait = false;
 
 	mutex_lock(&dcc->cmd_lock);
-
 	dc = (struct discard_cmd *)__lookup_rb_tree(&dcc->root, NULL, blkaddr);
 	if (dc) {
-		if (dc->state != D_PREP)
-			wait_for_completion_io(&dc->wait);
-		__punch_discard_cmd(sbi, dc, blkaddr);
+		if (dc->state == D_PREP) {
+			__punch_discard_cmd(sbi, dc, blkaddr);
+		} else {
+			dc->ref++;
+			need_wait = true;
+		}
 	}
-
 	mutex_unlock(&dcc->cmd_lock);
+
+	if (need_wait) {
+		wait_for_completion_io(&dc->wait);
+		mutex_lock(&dcc->cmd_lock);
+		f2fs_bug_on(sbi, dc->state != D_DONE);
+		dc->ref--;
+		if (!dc->ref)
+			__remove_discard_cmd(sbi, dc);
+		mutex_unlock(&dcc->cmd_lock);
+	}
 }
 
 /* This comes from f2fs_put_super */