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From:   Sahitya Tummala <stummala@codeaurora.org>
To:     Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <yuchao0@huawei.com>,
        linux-f2fs-devel@lists.sourceforge.net
Cc:     Sahitya Tummala <stummala@codeaurora.org>,
        linux-kernel@vger.kernel.org
Subject: [PATCH v3] f2fs: fix long latency due to discard during umount
Date:   Mon, 30 Mar 2020 12:15:30 +0530
Message-Id: <1585550730-1858-1-git-send-email-stummala@codeaurora.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

F2FS already has a default timeout of 5 secs for discards that
can be issued during umount, but it can take more than the 5 sec
timeout if the underlying UFS device queue is already full and there
are no more available free tags to be used. In that case, submit_bio()
will wait for the already queued discard requests to complete to get
a free tag, which can potentially take way more than 5 sec.

Fix this by submitting the discard requests with REQ_NOWAIT
flags during umount. This will return -EAGAIN for UFS queue/tag full
scenario without waiting in the context of submit_bio(). The FS can
then handle these requests by retrying again within the stipulated
discard timeout period to avoid long latencies.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
---
v3:
-Handle the regression reported by Chao with v2.
-simplify the logic to split the dc with multiple bios incase any bio returns
 EAGAIN and retry those new dc within 5 sec timeout.

 fs/f2fs/segment.c | 65 +++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 51 insertions(+), 14 deletions(-)

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index fb3e531..55d18c7 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -1029,13 +1029,16 @@ static void f2fs_submit_discard_endio(struct bio *bio)
 	struct discard_cmd *dc = (struct discard_cmd *)bio->bi_private;
 	unsigned long flags;
 
-	dc->error = blk_status_to_errno(bio->bi_status);
-
 	spin_lock_irqsave(&dc->lock, flags);
+	if (!dc->error)
+		dc->error = blk_status_to_errno(bio->bi_status);
+
 	dc->bio_ref--;
-	if (!dc->bio_ref && dc->state == D_SUBMIT) {
-		dc->state = D_DONE;
-		complete_all(&dc->wait);
+	if (!dc->bio_ref) {
+		if (dc->error || dc->state == D_SUBMIT) {
+			dc->state = D_DONE;
+			complete_all(&dc->wait);
+		}
 	}
 	spin_unlock_irqrestore(&dc->lock, flags);
 	bio_put(bio);
@@ -1124,10 +1127,13 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
 	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);
-	int flag = dpolicy->sync ? REQ_SYNC : 0;
+	int flag;
 	block_t lstart, start, len, total_len;
 	int err = 0;
 
+	flag = dpolicy->sync ? REQ_SYNC : 0;
+	flag |= dpolicy->type == DPOLICY_UMOUNT ? REQ_NOWAIT : 0;
+
 	if (dc->state != D_PREP)
 		return 0;
 
@@ -1192,10 +1198,6 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
 		dc->bio_ref++;
 		spin_unlock_irqrestore(&dc->lock, flags);
 
-		atomic_inc(&dcc->queued_discard);
-		dc->queued++;
-		list_move_tail(&dc->list, wait_list);
-
 		/* sanity check on discard range */
 		__check_sit_bitmap(sbi, lstart, lstart + len);
 
@@ -1203,6 +1205,29 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
 		bio->bi_end_io = f2fs_submit_discard_endio;
 		bio->bi_opf |= flag;
 		submit_bio(bio);
+		if (flag & REQ_NOWAIT) {
+			if (dc->error == -EAGAIN) {
+				spin_lock_irqsave(&dc->lock, flags);
+				dc->len -= len;
+				if (!dc->len) {
+					dc->len = total_len;
+					dc->state = D_PREP;
+					reinit_completion(&dc->wait);
+				} else {
+					dcc->undiscard_blks -= total_len;
+					if (dc->state == D_PARTIAL)
+						dc->state = D_SUBMIT;
+				}
+				err = dc->error;
+				dc->error = 0;
+				spin_unlock_irqrestore(&dc->lock, flags);
+				break;
+			}
+		}
+
+		atomic_inc(&dcc->queued_discard);
+		dc->queued++;
+		list_move_tail(&dc->list, wait_list);
 
 		atomic_inc(&dcc->issued_discard);
 
@@ -1214,8 +1239,9 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
 		len = total_len;
 	}
 
-	if (!err && len)
-		__update_discard_tree_range(sbi, bdev, lstart, start, len);
+	if ((!err || err == -EAGAIN) && total_len && dc->start != start)
+		__update_discard_tree_range(sbi, bdev, lstart, start,
+					total_len);
 	return err;
 }
 
@@ -1470,12 +1496,15 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 	struct list_head *pend_list;
 	struct discard_cmd *dc, *tmp;
 	struct blk_plug plug;
-	int i, issued = 0;
+	int i, err, issued = 0;
 	bool io_interrupted = false;
+	bool retry;
 
 	if (dpolicy->timeout != 0)
 		f2fs_update_time(sbi, dpolicy->timeout);
 
+retry:
+	retry = false;
 	for (i = MAX_PLIST_NUM - 1; i >= 0; i--) {
 		if (dpolicy->timeout != 0 &&
 				f2fs_time_over(sbi, dpolicy->timeout))
@@ -1509,7 +1538,12 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 				break;
 			}
 
-			__submit_discard_cmd(sbi, dpolicy, dc, &issued);
+			err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
+			if (err == -EAGAIN) {
+				congestion_wait(BLK_RW_ASYNC,
+						DEFAULT_IO_TIMEOUT);
+				retry = true;
+			}
 
 			if (issued >= dpolicy->max_requests)
 				break;
@@ -1522,6 +1556,9 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 			break;
 	}
 
+	if (retry)
+		goto retry;
+
 	if (!issued && io_interrupted)
 		issued = -1;
 
-- 
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Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.