lightnvm: pblk: avoid being reported as hung on rated GC

The amount of GC I/O on the write buffer is managed by the rate-limiter,
which is calculated as a function of the number of available free
blocks. When reaching the stable point, we risk having scheduled more
I/Os for GC than are allowed on the write buffer. This would result on
the GC semaphore balancing the outstanding read GC I/Os to be reported
as "hung", though the behavior is normal.

Solve this by allowing to schedule when we detect that the read GC path
is not moving forward.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/lightnvm/pblk-gc.c b/drivers/lightnvm/pblk-gc.c
index b8323e3..00d5698 100644 (file)
--- a/drivers/lightnvm/pblk-gc.c
+++ b/drivers/lightnvm/pblk-gc.c
@@ -218,7 +218,13 @@ next_rq:
        gc_rq_ws->line = line;
        gc_rq_ws->priv = gc_rq;
 
-       down(&gc->gc_sem);
+       /* The write GC path can be much slower than the read GC one due to
+        * the budget imposed by the rate-limiter. Balance in case that we get
+        * back pressure from the write GC path.
+        */
+       while (down_timeout(&gc->gc_sem, msecs_to_jiffies(30000)))
+               io_schedule();
+
        kref_get(&line->ref);
 
        INIT_WORK(&gc_rq_ws->ws, pblk_gc_line_ws);