lightnvm: pblk: set conservative threshold for user writes

In a worst-case scenario (random writes), OP% of sectors
in each line will be invalid, and we will then need
to move data out of 100/OP% lines to free a single line.

So, to prevent the possibility of running out of lines,
temporarily block user writes when there is less than
100/OP% free lines.

Also ensure that pblk creation does not produce instances
with insufficient over provisioning.

Insufficient over-provising is not a problem on real hardware,
but often an issue when running QEMU simulations (with few lines).
100 lines is enough to create a sane instance with the standard
(11%) over provisioning.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Reviewed-by: Javier González <javier@javigon.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 11 insertions, 1 deletions

diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
index f415aae600c8..e5b88a25d4d6 100644
--- a/drivers/lightnvm/pblk.h
+++ b/drivers/lightnvm/pblk.h
@@ -905,7 +905,6 @@ int pblk_recov_check_emeta(struct pblk *pblk, struct line_emeta *emeta);
 #define PBLK_GC_MAX_READERS 8	/* Max number of outstanding GC reader jobs */
 #define PBLK_GC_RQ_QD 128	/* Queue depth for inflight GC requests */
 #define PBLK_GC_L_QD 4		/* Queue depth for inflight GC lines */
-#define PBLK_GC_RSV_LINE 1	/* Reserved lines for GC */
 
 int pblk_gc_init(struct pblk *pblk);
 void pblk_gc_exit(struct pblk *pblk, bool graceful);
@@ -1370,4 +1369,15 @@ static inline char *pblk_disk_name(struct pblk *pblk)
 
 	return disk->disk_name;
 }
+
+static inline unsigned int pblk_get_min_chks(struct pblk *pblk)
+{
+	struct pblk_line_meta *lm = &pblk->lm;
+	/* In a worst-case scenario every line will have OP invalid sectors.
+	 * We will then need a minimum of 1/OP lines to free up a single line
+	 */
+
+	return DIV_ROUND_UP(100, pblk->op) * lm->blk_per_line;
+
+}
 #endif /* PBLK_H_ */