[PATCH V2] lightnvm: pblk: extend line wp balance check

[hans]

From: Hans Holmberg <hans.holmberg@xxxxxxxxxxxx>

pblk stripes writes of minimal write size across all non-offline chunks
in a line, which means that the maximum write pointer delta should not
exceed the minimal write size.

Extend the line write pointer balance check to cover this case, and
ignore the offline chunk wps.

This will render us a warning during recovery if something unexpected
has happened to the chunk write pointers (i.e. powerloss,  a spurious
chunk reset, ..).

Reported-by: Zhoujie Wu <zjwu@xxxxxxxxxxx>
Tested-by: Zhoujie Wu <zjwu@xxxxxxxxxxx>
Signed-off-by: Hans Holmberg <hans.holmberg@xxxxxxxxxxxx>
---

Changes since V1:

	* Squashed with Zhoujie's:
	 "lightnvm: pblk: ignore bad block wp for pblk_line_wp_is_unbalanced"
	* Clarified commit message based on Javier's comments.
		

 drivers/lightnvm/pblk-recovery.c | 56 ++++++++++++++++++++++----------
 1 file changed, 38 insertions(+), 18 deletions(-)

diff --git a/drivers/lightnvm/pblk-recovery.c b/drivers/lightnvm/pblk-recovery.c
index 6761d2afa4d0..d86f580036d3 100644
--- a/drivers/lightnvm/pblk-recovery.c
+++ b/drivers/lightnvm/pblk-recovery.c
@@ -302,35 +302,55 @@ static int pblk_pad_distance(struct pblk *pblk, struct pblk_line *line)
 	return (distance > line->left_msecs) ? line->left_msecs : distance;
 }
 
-static int pblk_line_wp_is_unbalanced(struct pblk *pblk,
-				      struct pblk_line *line)
+/* Return a chunk belonging to a line by stripe(write order) index */
+static struct nvm_chk_meta *pblk_get_stripe_chunk(struct pblk *pblk,
+						  struct pblk_line *line,
+						  int index)
 {
 	struct nvm_tgt_dev *dev = pblk->dev;
 	struct nvm_geo *geo = &dev->geo;
-	struct pblk_line_meta *lm = &pblk->lm;
 	struct pblk_lun *rlun;
-	struct nvm_chk_meta *chunk;
 	struct ppa_addr ppa;
-	u64 line_wp;
-	int pos, i;
+	int pos;
 
-	rlun = &pblk->luns[0];
+	rlun = &pblk->luns[index];
 	ppa = rlun->bppa;
 	pos = pblk_ppa_to_pos(geo, ppa);
-	chunk = &line->chks[pos];
 
-	line_wp = chunk->wp;
+	return &line->chks[pos];
+}
 
-	for (i = 1; i < lm->blk_per_line; i++) {
-		rlun = &pblk->luns[i];
-		ppa = rlun->bppa;
-		pos = pblk_ppa_to_pos(geo, ppa);
-		chunk = &line->chks[pos];
+static int pblk_line_wps_are_unbalanced(struct pblk *pblk,
+				      struct pblk_line *line)
+{
+	struct pblk_line_meta *lm = &pblk->lm;
+	int blk_in_line = lm->blk_per_line;
+	struct nvm_chk_meta *chunk;
+	u64 max_wp, min_wp;
+	int i;
+
+	i = find_first_zero_bit(line->blk_bitmap, blk_in_line);
 
-		if (chunk->wp > line_wp)
+	/* If there is one or zero good chunks in the line,
+	 * the write pointers can't be unbalanced.
+	 */
+	if (i >= (blk_in_line - 1))
+		return 0;
+
+	chunk = pblk_get_stripe_chunk(pblk, line, i);
+	max_wp = chunk->wp;
+	if (max_wp > pblk->max_write_pgs)
+		min_wp = max_wp - pblk->max_write_pgs;
+	else
+		min_wp = 0;
+
+	i = find_next_zero_bit(line->blk_bitmap, blk_in_line, i + 1);
+	while (i < blk_in_line) {
+		chunk = pblk_get_stripe_chunk(pblk, line, i);
+		if (chunk->wp > max_wp || chunk->wp < min_wp)
 			return 1;
-		else if (chunk->wp < line_wp)
-			line_wp = chunk->wp;
+
+		i = find_next_zero_bit(line->blk_bitmap, blk_in_line, i + 1);
 	}
 
 	return 0;
@@ -356,7 +376,7 @@ static int pblk_recov_scan_oob(struct pblk *pblk, struct pblk_line *line,
 	int ret;
 	u64 left_ppas = pblk_sec_in_open_line(pblk, line) - lm->smeta_sec;
 
-	if (pblk_line_wp_is_unbalanced(pblk, line))
+	if (pblk_line_wps_are_unbalanced(pblk, line))
 		pblk_warn(pblk, "recovering unbalanced line (%d)\n", line->id);
 
 	ppa_list = p.ppa_list;
-- 
2.17.1