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, 31 insertions, 9 deletions

diff --git a/drivers/lightnvm/pblk-init.c b/drivers/lightnvm/pblk-init.c
index 13822594647c..f083130d9920 100644
--- a/drivers/lightnvm/pblk-init.c
+++ b/drivers/lightnvm/pblk-init.c
@@ -635,7 +635,7 @@ static unsigned int calc_emeta_len(struct pblk *pblk)
         return (lm->emeta_len[1] + lm->emeta_len[2] + lm->emeta_len[3]);
 }
 
-static void pblk_set_provision(struct pblk *pblk, long nr_free_blks)
+static int pblk_set_provision(struct pblk *pblk, int nr_free_chks)
 {
         struct nvm_tgt_dev *dev = pblk->dev;
         struct pblk_line_mgmt *l_mg = &pblk->l_mg;
@@ -643,23 +643,41 @@ static void pblk_set_provision(struct pblk *pblk, long nr_free_blks)
         struct nvm_geo *geo = &dev->geo;
         sector_t provisioned;
         int sec_meta, blk_meta;
+        int minimum;
 
         if (geo->op == NVM_TARGET_DEFAULT_OP)
                 pblk->op = PBLK_DEFAULT_OP;
         else
                 pblk->op = geo->op;
 
-        provisioned = nr_free_blks;
+        minimum = pblk_get_min_chks(pblk);
+        provisioned = nr_free_chks;
         provisioned *= (100 - pblk->op);
         sector_div(provisioned, 100);
 
-        pblk->op_blks = nr_free_blks - provisioned;
+        if ((nr_free_chks - provisioned) < minimum) {
+                if (geo->op != NVM_TARGET_DEFAULT_OP) {
+                        pblk_err(pblk, "OP too small to create a sane instance\n");
+                        return -EINTR;
+                }
+
+                /* If the user did not specify an OP value, and PBLK_DEFAULT_OP
+                 * is not enough, calculate and set sane value
+                 */
+
+                provisioned = nr_free_chks - minimum;
+                pblk->op =  (100 * minimum) / nr_free_chks;
+                pblk_info(pblk, "Default OP insufficient, adjusting OP to %d\n",
+                                pblk->op);
+        }
+
+        pblk->op_blks = nr_free_chks - provisioned;
 
         /* Internally pblk manages all free blocks, but all calculations based
          * on user capacity consider only provisioned blocks
          */
-        pblk->rl.total_blocks = nr_free_blks;
-        pblk->rl.nr_secs = nr_free_blks * geo->clba;
+        pblk->rl.total_blocks = nr_free_chks;
+        pblk->rl.nr_secs = nr_free_chks * geo->clba;
 
         /* Consider sectors used for metadata */
         sec_meta = (lm->smeta_sec + lm->emeta_sec[0]) * l_mg->nr_free_lines;
@@ -667,8 +685,10 @@ static void pblk_set_provision(struct pblk *pblk, long nr_free_blks)
 
         pblk->capacity = (provisioned - blk_meta) * geo->clba;
 
-        atomic_set(&pblk->rl.free_blocks, nr_free_blks);
-        atomic_set(&pblk->rl.free_user_blocks, nr_free_blks);
+        atomic_set(&pblk->rl.free_blocks, nr_free_chks);
+        atomic_set(&pblk->rl.free_user_blocks, nr_free_chks);
+
+        return 0;
 }
 
 static int pblk_setup_line_meta_chk(struct pblk *pblk, struct pblk_line *line,
@@ -984,7 +1004,7 @@ static int pblk_lines_init(struct pblk *pblk)
         struct pblk_line_mgmt *l_mg = &pblk->l_mg;
         struct pblk_line *line;
         void *chunk_meta;
-        long nr_free_chks = 0;
+        int nr_free_chks = 0;
         int i, ret;
 
         ret = pblk_line_meta_init(pblk);
@@ -1031,7 +1051,9 @@ static int pblk_lines_init(struct pblk *pblk)
                 goto fail_free_lines;
         }
 
-        pblk_set_provision(pblk, nr_free_chks);
+        ret = pblk_set_provision(pblk, nr_free_chks);
+        if (ret)
+                goto fail_free_lines;
 
         vfree(chunk_meta);
         return 0;