mtd: ubi: wl: avoid erasing a PEB which is empty

wear_leveling_worker() currently unconditionally puts a PEB on erase in
the error case even it just been taken from the free_list and never
used.
In case the PEB was never used it can be put back on the free list
saving a precious erase cycle.

v1…v2:
	- to_leb_clean -> dst_leb_clean
	- use the nested option for ensure_wear_leveling()
	- do_sync_erase() can't go -ENOMEM so we can just go into
	  RO-mode now.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Richard Weinberger <richard@nod.at>

1 files changed, 18 insertions, 3 deletions

diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 56065632a5b8..17ec948ac40e 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -628,6 +628,7 @@ static int do_sync_erase(struct ubi_device *ubi, struct ubi_wl_entry *e,
         return __erase_worker(ubi, &wl_wrk);
 }
 
+static int ensure_wear_leveling(struct ubi_device *ubi, int nested);
 /**
  * wear_leveling_worker - wear-leveling worker function.
  * @ubi: UBI device description object
@@ -649,6 +650,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 #endif
         struct ubi_wl_entry *e1, *e2;
         struct ubi_vid_hdr *vid_hdr;
+        int dst_leb_clean = 0;
 
         kfree(wrk);
         if (shutdown)
@@ -753,6 +755,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
 
         err = ubi_io_read_vid_hdr(ubi, e1->pnum, vid_hdr, 0);
         if (err && err != UBI_IO_BITFLIPS) {
+                dst_leb_clean = 1;
                 if (err == UBI_IO_FF) {
                         /*
                          * We are trying to move PEB without a VID header. UBI
@@ -798,10 +801,12 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
                          * protection queue.
                          */
                         protect = 1;
+                        dst_leb_clean = 1;
                         goto out_not_moved;
                 }
                 if (err == MOVE_RETRY) {
                         scrubbing = 1;
+                        dst_leb_clean = 1;
                         goto out_not_moved;
                 }
                 if (err == MOVE_TARGET_BITFLIPS || err == MOVE_TARGET_WR_ERR ||
@@ -827,6 +832,7 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
                                         ubi->erroneous_peb_count);
                                 goto out_error;
                         }
+                        dst_leb_clean = 1;
                         erroneous = 1;
                         goto out_not_moved;
                 }
@@ -897,15 +903,24 @@ out_not_moved:
                 wl_tree_add(e1, &ubi->scrub);
         else
                 wl_tree_add(e1, &ubi->used);
+        if (dst_leb_clean) {
+                wl_tree_add(e2, &ubi->free);
+                ubi->free_count++;
+        }
+
         ubi_assert(!ubi->move_to_put);
         ubi->move_from = ubi->move_to = NULL;
         ubi->wl_scheduled = 0;
         spin_unlock(&ubi->wl_lock);
 
         ubi_free_vid_hdr(ubi, vid_hdr);
-        err = do_sync_erase(ubi, e2, vol_id, lnum, torture);
-        if (err)
-                goto out_ro;
+        if (dst_leb_clean) {
+                ensure_wear_leveling(ubi, 1);
+        } else {
+                err = do_sync_erase(ubi, e2, vol_id, lnum, torture);
+                if (err)
+                        goto out_ro;
+        }
 
         mutex_unlock(&ubi->move_mutex);
         return 0;