lightnvm: pblk: prevent stall due to wb threshold
In order to respect mw_cuinits, pblk's write buffer maintains a
backpointer to protect data not yet persisted; when writing to the write
buffer, this backpointer defines a threshold that pblk's rate-limiter
enforces.
On small PU configurations, the following scenarios might take place: (i)
the threshold is larger than the write buffer and (ii) the threshold is
smaller than the write buffer, but larger than the maximun allowed
split bio - 256KB at this moment (Note that writes are not always
split - we only do this when we the size of the buffer is smaller
than the buffer). In both cases, pblk's rate-limiter prevents the I/O to
be written to the buffer, thus stalling.
This patch fixes the original backpointer implementation by considering
the threshold both on buffer creation and on the rate-limiters path,
when bio_split is triggered (case (ii) above).
Fixes: 766c8ceb16fc ("lightnvm: pblk: guarantee that backpointer is respected on writer stall")
Signed-off-by: Javier González <javier@javigon.com>
Reviewed-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/lightnvm/pblk-rl.c b/drivers/lightnvm/pblk-rl.c
index 76116d5..b014957 100644
--- a/drivers/lightnvm/pblk-rl.c
+++ b/drivers/lightnvm/pblk-rl.c
@@ -207,7 +207,7 @@ void pblk_rl_free(struct pblk_rl *rl)
del_timer(&rl->u_timer);
}
-void pblk_rl_init(struct pblk_rl *rl, int budget)
+void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold)
{
struct pblk *pblk = container_of(rl, struct pblk, rl);
struct nvm_tgt_dev *dev = pblk->dev;
@@ -217,7 +217,6 @@ void pblk_rl_init(struct pblk_rl *rl, int budget)
int sec_meta, blk_meta;
unsigned int rb_windows;
-
/* Consider sectors used for metadata */
sec_meta = (lm->smeta_sec + lm->emeta_sec[0]) * l_mg->nr_free_lines;
blk_meta = DIV_ROUND_UP(sec_meta, geo->clba);
@@ -234,7 +233,7 @@ void pblk_rl_init(struct pblk_rl *rl, int budget)
/* To start with, all buffer is available to user I/O writers */
rl->rb_budget = budget;
rl->rb_user_max = budget;
- rl->rb_max_io = budget >> 1;
+ rl->rb_max_io = threshold ? (budget - threshold) : (budget - 1);
rl->rb_gc_max = 0;
rl->rb_state = PBLK_RL_HIGH;