[PATCH V2] lightnvm: pblk: prevent stall due to wb threshold

[PATCH V2] lightnvm: pblk: prevent stall due to wb threshold

[Javier González]

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>
---

  Changes since V1:
    - Fix a bad arithmetinc on the rate-limiter max_io calculation (from
      Hans)

 drivers/lightnvm/pblk-rb.c | 25 +++++++++++++++++++------
 drivers/lightnvm/pblk-rl.c |  5 ++---
 drivers/lightnvm/pblk.h    |  2 +-
 3 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
index d4ca8c64ee0f..a6133b50ed9c 100644
--- 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 76116d5f78e4..e9e0af0df165 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 = budget - threshold;
 	rl->rb_gc_max = 0;
 	rl->rb_state = PBLK_RL_HIGH;
 
diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
index 72ae8755764e..a6386d5acd73 100644
--- 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);
-- 
2.17.1

Re: [PATCH V2] lightnvm: pblk: prevent stall due to wb threshold

[Matias Bjørling]

On 1/30/19 11:26 AM, Javier González wrote:
> 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>
> ---
> 
>    Changes since V1:
>      - Fix a bad arithmetinc on the rate-limiter max_io calculation (from
>        Hans)
> 
>   drivers/lightnvm/pblk-rb.c | 25 +++++++++++++++++++------
>   drivers/lightnvm/pblk-rl.c |  5 ++---
>   drivers/lightnvm/pblk.h    |  2 +-
>   3 files changed, 22 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
> index d4ca8c64ee0f..a6133b50ed9c 100644
> --- 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 76116d5f78e4..e9e0af0df165 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 = budget - threshold;
>   	rl->rb_gc_max = 0;
>   	rl->rb_state = PBLK_RL_HIGH;
>   
> diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
> index 72ae8755764e..a6386d5acd73 100644
> --- 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);
> 

Thanks Javier. Applied for 5.1.

Re: [PATCH V2] lightnvm: pblk: prevent stall due to wb threshold

[Hans Holmberg]

Hi Javier!

How did you test this? I'm trying to add a test case to our testing framework.

This is what i ran in qemu, and I got a hang (with this version of the patch)

nvme lnvm create -d nvme0n1 -t pblk -n pblk0 -f -b 0 -e 0

kernel log: [  116.381799] pblk pblk0: luns:1, lines:280, secs:212736,
buf entries:128

# dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=4k count=1
1+0 records in
1+0 records out
4096 bytes (4.1 kB, 4.0 KiB) copied, 0.000480941 s, 8.5 MB/s
# dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=64k count=1
1+0 records in
1+0 records out
65536 bytes (66 kB, 64 KiB) copied, 0.000477373 s, 137 MB/s
# dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=128k count=1
1+0 records in
1+0 records out
131072 bytes (131 kB, 128 KiB) copied, 0.000548722 s, 239 MB/s
# dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=256k count=1
1+0 records in
1+0 records out
262144 bytes (262 kB, 256 KiB) copied, 0.000718515 s, 365 MB/s
# dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=512k count=1
<HANG>


On Wed, Jan 30, 2019 at 11:28 AM Javier González <javier@javigon.com> wrote:
>
> 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>
> ---
>
>   Changes since V1:
>     - Fix a bad arithmetinc on the rate-limiter max_io calculation (from
>       Hans)
>
>  drivers/lightnvm/pblk-rb.c | 25 +++++++++++++++++++------
>  drivers/lightnvm/pblk-rl.c |  5 ++---
>  drivers/lightnvm/pblk.h    |  2 +-
>  3 files changed, 22 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
> index d4ca8c64ee0f..a6133b50ed9c 100644
> --- 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 76116d5f78e4..e9e0af0df165 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 = budget - threshold;
>         rl->rb_gc_max = 0;
>         rl->rb_state = PBLK_RL_HIGH;
>
> diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
> index 72ae8755764e..a6386d5acd73 100644
> --- 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);
> --
> 2.17.1
>

Re: [PATCH V2] lightnvm: pblk: prevent stall due to wb threshold

[Javier González]

> On 31 Jan 2019, at 11.41, Hans Holmberg <hans@owltronix.com> wrote:
> 
> Hi Javier!
> 
> How did you test this? I'm trying to add a test case to our testing framework.
> 
> This is what i ran in qemu, and I got a hang (with this version of the patch)
> 
> nvme lnvm create -d nvme0n1 -t pblk -n pblk0 -f -b 0 -e 0

I run several low configurations without problem. Can you share the qemu configuration and version?

I’m on travel until Friday - I’ll come back to you over the weekend. 

> 
> kernel log: [  116.381799] pblk pblk0: luns:1, lines:280, secs:212736,
> buf entries:128
> 
> # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=4k count=1
> 1+0 records in
> 1+0 records out
> 4096 bytes (4.1 kB, 4.0 KiB) copied, 0.000480941 s, 8.5 MB/s
> # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=64k count=1
> 1+0 records in
> 1+0 records out
> 65536 bytes (66 kB, 64 KiB) copied, 0.000477373 s, 137 MB/s
> # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=128k count=1
> 1+0 records in
> 1+0 records out
> 131072 bytes (131 kB, 128 KiB) copied, 0.000548722 s, 239 MB/s
> # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=256k count=1
> 1+0 records in
> 1+0 records out
> 262144 bytes (262 kB, 256 KiB) copied, 0.000718515 s, 365 MB/s
> # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=512k count=1
> <HANG>


> 
> 
>> On Wed, Jan 30, 2019 at 11:28 AM Javier González <javier@javigon.com> wrote:
>> 
>> 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>
>> ---
>> 
>>  Changes since V1:
>>    - Fix a bad arithmetinc on the rate-limiter max_io calculation (from
>>      Hans)
>> 
>> drivers/lightnvm/pblk-rb.c | 25 +++++++++++++++++++------
>> drivers/lightnvm/pblk-rl.c |  5 ++---
>> drivers/lightnvm/pblk.h    |  2 +-
>> 3 files changed, 22 insertions(+), 10 deletions(-)
>> 
>> diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
>> index d4ca8c64ee0f..a6133b50ed9c 100644
>> --- 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 76116d5f78e4..e9e0af0df165 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 = budget - threshold;
>>        rl->rb_gc_max = 0;
>>        rl->rb_state = PBLK_RL_HIGH;
>> 
>> diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
>> index 72ae8755764e..a6386d5acd73 100644
>> --- 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);
>> --
>> 2.17.1
>> 

Re: [PATCH V2] lightnvm: pblk: prevent stall due to wb threshold

[Hans Holmberg]

On Thu, Jan 31, 2019 at 5:33 PM Javier González <javier@javigon.com> wrote:
>
>
>
> > On 31 Jan 2019, at 11.41, Hans Holmberg <hans@owltronix.com> wrote:
> >
> > Hi Javier!
> >
> > How did you test this? I'm trying to add a test case to our testing framework.
> >
> > This is what i ran in qemu, and I got a hang (with this version of the patch)
> >
> > nvme lnvm create -d nvme0n1 -t pblk -n pblk0 -f -b 0 -e 0
>
> I run several low configurations without problem. Can you share the qemu configuration and version?
>

Of course!

qemu remote: https://github.com/CNEX-Labs/qemu-nvme.git
branch: master (cb200e3ccf9c1ff21f6275c6cb68b2801135a640)

My geometry:
parallel units: 8, secs per chk: 768, meta size 16, ws min 12, ws opt
24, cunits=0

> I’m on travel until Friday - I’ll come back to you over the weekend.

Oh, no worries. This patch did not introduce the issue, so it's not a
regression, but it looks like the same type of hang as the patch
addresses.
I might have stumbled across another bug.

One thing I noticed was that the dd write block size that triggered
the hang is >= write buffer. (128 entries * 4k)

Safe travels!

>
> >
> > kernel log: [  116.381799] pblk pblk0: luns:1, lines:280, secs:212736,
> > buf entries:128
> >
> > # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=4k count=1
> > 1+0 records in
> > 1+0 records out
> > 4096 bytes (4.1 kB, 4.0 KiB) copied, 0.000480941 s, 8.5 MB/s
> > # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=64k count=1
> > 1+0 records in
> > 1+0 records out
> > 65536 bytes (66 kB, 64 KiB) copied, 0.000477373 s, 137 MB/s
> > # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=128k count=1
> > 1+0 records in
> > 1+0 records out
> > 131072 bytes (131 kB, 128 KiB) copied, 0.000548722 s, 239 MB/s
> > # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=256k count=1
> > 1+0 records in
> > 1+0 records out
> > 262144 bytes (262 kB, 256 KiB) copied, 0.000718515 s, 365 MB/s
> > # dd if=/dev/zero of=/dev/pblk0 oflag=direct bs=512k count=1
> > <HANG>
>
>
> >
> >
> >> On Wed, Jan 30, 2019 at 11:28 AM Javier González <javier@javigon.com> wrote:
> >>
> >> 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>
> >> ---
> >>
> >>  Changes since V1:
> >>    - Fix a bad arithmetinc on the rate-limiter max_io calculation (from
> >>      Hans)
> >>
> >> drivers/lightnvm/pblk-rb.c | 25 +++++++++++++++++++------
> >> drivers/lightnvm/pblk-rl.c |  5 ++---
> >> drivers/lightnvm/pblk.h    |  2 +-
> >> 3 files changed, 22 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
> >> index d4ca8c64ee0f..a6133b50ed9c 100644
> >> --- 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 76116d5f78e4..e9e0af0df165 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 = budget - threshold;
> >>        rl->rb_gc_max = 0;
> >>        rl->rb_state = PBLK_RL_HIGH;
> >>
> >> diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
> >> index 72ae8755764e..a6386d5acd73 100644
> >> --- 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);
> >> --
> >> 2.17.1
> >>

Re: [PATCH V2] lightnvm: pblk: prevent stall due to wb threshold

[Javier González]

[-- Attachment #1: Type: text/plain, Size: 4696 bytes --]


> On 31 Jan 2019, at 21.10, Hans Holmberg <hans@owltronix.com> wrote:
> 
> On Thu, Jan 31, 2019 at 5:33 PM Javier González <javier@javigon.com> wrote:
>>> On 31 Jan 2019, at 11.41, Hans Holmberg <hans@owltronix.com> wrote:
>>> 
>>> Hi Javier!
>>> 
>>> How did you test this? I'm trying to add a test case to our testing framework.
>>> 
>>> This is what i ran in qemu, and I got a hang (with this version of the patch)
>>> 
>>> nvme lnvm create -d nvme0n1 -t pblk -n pblk0 -f -b 0 -e 0
>> 
>> I run several low configurations without problem. Can you share the qemu configuration and version?
> 
> Of course!
> 
> qemu remote: https://github.com/CNEX-Labs/qemu-nvme.git
> branch: master (cb200e3ccf9c1ff21f6275c6cb68b2801135a640)
> 
> My geometry:
> parallel units: 8, secs per chk: 768, meta size 16, ws min 12, ws opt
> 24, cunits=0

You are right, lmw_cunits=0 gives the problem.

What about the following? If it goes through cijoe, I'll send a V3.

diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
index d4ca8c64ee0f..a6133b50ed9c 100644
--- 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 76116d5f78e4..b014957dde0b 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;

diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
index 72ae8755764e..a6386d5acd73 100644
--- 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);
--
2.17.1


[-- Attachment #2: Message signed with OpenPGP --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

Re: [PATCH V2] lightnvm: pblk: prevent stall due to wb threshold

[Hans Holmberg]

On Mon, Feb 4, 2019 at 9:14 AM Javier González <javier@javigon.com> wrote:
>
>
> > On 31 Jan 2019, at 21.10, Hans Holmberg <hans@owltronix.com> wrote:
> >
> > On Thu, Jan 31, 2019 at 5:33 PM Javier González <javier@javigon.com> wrote:
> >>> On 31 Jan 2019, at 11.41, Hans Holmberg <hans@owltronix.com> wrote:
> >>>
> >>> Hi Javier!
> >>>
> >>> How did you test this? I'm trying to add a test case to our testing framework.
> >>>
> >>> This is what i ran in qemu, and I got a hang (with this version of the patch)
> >>>
> >>> nvme lnvm create -d nvme0n1 -t pblk -n pblk0 -f -b 0 -e 0
> >>
> >> I run several low configurations without problem. Can you share the qemu configuration and version?
> >
> > Of course!
> >
> > qemu remote: https://github.com/CNEX-Labs/qemu-nvme.git
> > branch: master (cb200e3ccf9c1ff21f6275c6cb68b2801135a640)
> >
> > My geometry:
> > parallel units: 8, secs per chk: 768, meta size 16, ws min 12, ws opt
> > 24, cunits=0
>
> You are right, lmw_cunits=0 gives the problem.
>
> What about the following? If it goes through cijoe, I'll send a V3.

Please do send a V3 if it passes your testing.

Thanks!
Hans

>
> diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
> index d4ca8c64ee0f..a6133b50ed9c 100644
> --- 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 76116d5f78e4..b014957dde0b 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;
>
> diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
> index 72ae8755764e..a6386d5acd73 100644
> --- 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);
> --
> 2.17.1
>