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-rb.c b/drivers/lightnvm/pblk-rb.c
index d4ca8c6..a6133b5 100644 (file)
--- a/drivers/lightnvm/pblk-rb.c
+++ b/drivers/lightnvm/pblk-rb.c
@@ -45,10 +45,23 @@ void pblk_rb_free(struct pblk_rb *rb)
 /*
  * pblk_rb_calculate_size -- calculate the size of the write buffer
  */
-static unsigned int pblk_rb_calculate_size(unsigned int nr_entries)
+static unsigned int pblk_rb_calculate_size(unsigned int nr_entries,
+                                          unsigned int threshold)
 {
-       /* Alloc a write buffer that can at least fit 128 entries */
-       return (1 << max(get_count_order(nr_entries), 7));
+       unsigned int thr_sz = 1 << (get_count_order(threshold + NVM_MAX_VLBA));
+       unsigned int max_sz = max(thr_sz, nr_entries);
+       unsigned int max_io;
+
+       /* Alloc a write buffer that can (i) fit at least two split bios
+        * (considering max I/O size NVM_MAX_VLBA, and (ii) guarantee that the
+        * threshold will be respected
+        */
+       max_io = (1 << max((int)(get_count_order(max_sz)),
+                               (int)(get_count_order(NVM_MAX_VLBA << 1))));
+       if ((threshold + NVM_MAX_VLBA) >= max_io)
+               max_io <<= 1;
+
+       return max_io;
 }
 
 /*
@@ -67,12 +80,12 @@ int pblk_rb_init(struct pblk_rb *rb, unsigned int size, unsigned int threshold,
        unsigned int alloc_order, order, iter;
        unsigned int nr_entries;
 
-       nr_entries = pblk_rb_calculate_size(size);
+       nr_entries = pblk_rb_calculate_size(size, threshold);
        entries = vzalloc(array_size(nr_entries, sizeof(struct pblk_rb_entry)));
        if (!entries)
                return -ENOMEM;
 
-       power_size = get_count_order(size);
+       power_size = get_count_order(nr_entries);
        power_seg_sz = get_count_order(seg_size);
 
        down_write(&pblk_rb_lock);
@@ -149,7 +162,7 @@ int pblk_rb_init(struct pblk_rb *rb, unsigned int size, unsigned int threshold,
         * Initialize rate-limiter, which controls access to the write buffer
         * by user and GC I/O
         */
-       pblk_rl_init(&pblk->rl, rb->nr_entries);
+       pblk_rl_init(&pblk->rl, rb->nr_entries, threshold);
 
        return 0;
 }

diff --git a/drivers/lightnvm/pblk-rl.c b/drivers/lightnvm/pblk-rl.c
index 76116d5..b014957 100644 (file)
--- 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;
 

diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
index 72ae875..a6386d5 100644 (file)
--- a/drivers/lightnvm/pblk.h
+++ b/drivers/lightnvm/pblk.h
@@ -924,7 +924,7 @@ int pblk_gc_sysfs_force(struct pblk *pblk, int force);
 /*
  * pblk rate limiter
  */
-void pblk_rl_init(struct pblk_rl *rl, int budget);
+void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold);
 void pblk_rl_free(struct pblk_rl *rl);
 void pblk_rl_update_rates(struct pblk_rl *rl);
 int pblk_rl_high_thrs(struct pblk_rl *rl);