Linux Virtualization - Jan 2021 - [PATCH v2 1/1] vhost scsi: alloc vhost_scsi with kvzalloc() to avoid delay

The size of 'struct vhost_scsi' is order-10 (~2.3MB). It may take long
time
delay by kzalloc() to compact memory pages by retrying multiple times when
there is a lack of high-order pages. As a result, there is latency to
create a VM (with vhost-scsi) or to hotadd vhost-scsi-based storage.

The prior commit 595cb754983d ("vhost/scsi: use vmalloc for order-10
allocation") prefers to fallback only when really needed, while this patch
allocates with kvzalloc() with __GFP_NORETRY implicitly set to avoid
retrying memory pages compact for multiple times.

The __GFP_NORETRY is implicitly set if the size to allocate is more than
PAGE_SZIE and when __GFP_RETRY_MAYFAIL is not explicitly set.

Cc: Aruna Ramakrishna <aruna.ramakrishna at oracle.com>
Cc: Joe Jin <joe.jin at oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang at oracle.com>
---
Changed since v1:
  - To combine kzalloc() and vzalloc() as kvzalloc()
    (suggested by Jason Wang)

 drivers/vhost/scsi.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 4ce9f00ae10e..5de21ad4bd05 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1814,12 +1814,9 @@ static int vhost_scsi_open(struct inode *inode, struct
file *f)
 	struct vhost_virtqueue **vqs;
 	int r = -ENOMEM, i;
 
-	vs = kzalloc(sizeof(*vs), GFP_KERNEL | __GFP_NOWARN | __GFP_RETRY_MAYFAIL);
-	if (!vs) {
-		vs = vzalloc(sizeof(*vs));
-		if (!vs)
-			goto err_vs;
-	}
+	vs = kvzalloc(sizeof(*vs), GFP_KERNEL);
+	if (!vs)
+		goto err_vs;
 
 	vqs = kmalloc_array(VHOST_SCSI_MAX_VQ, sizeof(*vqs), GFP_KERNEL);
 	if (!vqs)
-- 
2.17.1

According to my "git send-email" history, I have CCed jasowang at
redhat.com. Not
sure why Jason is not on the list.

CCed Jason. Thank you very much!

Dongli Zhang

On 1/23/21 12:08 AM, Dongli Zhang wrote:
> The size of 'struct vhost_scsi' is order-10 (~2.3MB). It may take
long time
> delay by kzalloc() to compact memory pages by retrying multiple times when
> there is a lack of high-order pages. As a result, there is latency to
> create a VM (with vhost-scsi) or to hotadd vhost-scsi-based storage.
> 
> The prior commit 595cb754983d ("vhost/scsi: use vmalloc for order-10
> allocation") prefers to fallback only when really needed, while this
patch
> allocates with kvzalloc() with __GFP_NORETRY implicitly set to avoid
> retrying memory pages compact for multiple times.
> 
> The __GFP_NORETRY is implicitly set if the size to allocate is more than
> PAGE_SZIE and when __GFP_RETRY_MAYFAIL is not explicitly set.
> 
> Cc: Aruna Ramakrishna <aruna.ramakrishna at oracle.com>
> Cc: Joe Jin <joe.jin at oracle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang at oracle.com>
> ---
> Changed since v1:
>   - To combine kzalloc() and vzalloc() as kvzalloc()
>     (suggested by Jason Wang)
> 
>  drivers/vhost/scsi.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> index 4ce9f00ae10e..5de21ad4bd05 100644
> --- a/drivers/vhost/scsi.c
> +++ b/drivers/vhost/scsi.c
> @@ -1814,12 +1814,9 @@ static int vhost_scsi_open(struct inode *inode,
struct file *f)
>  	struct vhost_virtqueue **vqs;
>  	int r = -ENOMEM, i;
>  
> -	vs = kzalloc(sizeof(*vs), GFP_KERNEL | __GFP_NOWARN |
__GFP_RETRY_MAYFAIL);
> -	if (!vs) {
> -		vs = vzalloc(sizeof(*vs));
> -		if (!vs)
> -			goto err_vs;
> -	}
> +	vs = kvzalloc(sizeof(*vs), GFP_KERNEL);
> +	if (!vs)
> +		goto err_vs;
>  
>  	vqs = kmalloc_array(VHOST_SCSI_MAX_VQ, sizeof(*vqs), GFP_KERNEL);
>  	if (!vqs)
>

On 2021/1/23 ??4:08, Dongli Zhang wrote:
> The size of 'struct vhost_scsi' is order-10 (~2.3MB). It may take
long time
> delay by kzalloc() to compact memory pages by retrying multiple times when
> there is a lack of high-order pages. As a result, there is latency to
> create a VM (with vhost-scsi) or to hotadd vhost-scsi-based storage.
>
> The prior commit 595cb754983d ("vhost/scsi: use vmalloc for order-10
> allocation") prefers to fallback only when really needed, while this
patch
> allocates with kvzalloc() with __GFP_NORETRY implicitly set to avoid
> retrying memory pages compact for multiple times.
>
> The __GFP_NORETRY is implicitly set if the size to allocate is more than
> PAGE_SZIE and when __GFP_RETRY_MAYFAIL is not explicitly set.
>
> Cc: Aruna Ramakrishna <aruna.ramakrishna at oracle.com>
> Cc: Joe Jin <joe.jin at oracle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang at oracle.com>
> ---
> Changed since v1:
>    - To combine kzalloc() and vzalloc() as kvzalloc()
>      (suggested by Jason Wang)
>
>   drivers/vhost/scsi.c | 9 +++------
>   1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> index 4ce9f00ae10e..5de21ad4bd05 100644
> --- a/drivers/vhost/scsi.c
> +++ b/drivers/vhost/scsi.c
> @@ -1814,12 +1814,9 @@ static int vhost_scsi_open(struct inode *inode,
struct file *f)
>   	struct vhost_virtqueue **vqs;
>   	int r = -ENOMEM, i;
>   
> -	vs = kzalloc(sizeof(*vs), GFP_KERNEL | __GFP_NOWARN |
__GFP_RETRY_MAYFAIL);
> -	if (!vs) {
> -		vs = vzalloc(sizeof(*vs));
> -		if (!vs)
> -			goto err_vs;
> -	}
> +	vs = kvzalloc(sizeof(*vs), GFP_KERNEL);
> +	if (!vs)
> +		goto err_vs;
>   
>   	vqs = kmalloc_array(VHOST_SCSI_MAX_VQ, sizeof(*vqs), GFP_KERNEL);
>   	if (!vqs)

Acked-by: Jason Wang <jasowang at redhat.com>

Can anyone help to review this patch and give a review-by for it please?

Thanks,
Joe
On 1/24/21 7:12 PM, Jason Wang wrote:
>
> On 2021/1/23 ??4:08, Dongli Zhang wrote:
>> The size of 'struct vhost_scsi' is order-10 (~2.3MB). It may
take long time
>> delay by kzalloc() to compact memory pages by retrying multiple times
when
>> there is a lack of high-order pages. As a result, there is latency to
>> create a VM (with vhost-scsi) or to hotadd vhost-scsi-based storage.
>>
>> The prior commit 595cb754983d ("vhost/scsi: use vmalloc for
order-10
>> allocation") prefers to fallback only when really needed, while
this patch
>> allocates with kvzalloc() with __GFP_NORETRY implicitly set to avoid
>> retrying memory pages compact for multiple times.
>>
>> The __GFP_NORETRY is implicitly set if the size to allocate is more
than
>> PAGE_SZIE and when __GFP_RETRY_MAYFAIL is not explicitly set.
>>
>> Cc: Aruna Ramakrishna <aruna.ramakrishna at oracle.com>
>> Cc: Joe Jin <joe.jin at oracle.com>
>> Signed-off-by: Dongli Zhang <dongli.zhang at oracle.com>
>> ---
>> Changed since v1:
>> ?? - To combine kzalloc() and vzalloc() as kvzalloc()
>> ???? (suggested by Jason Wang)
>>
>> ? drivers/vhost/scsi.c | 9 +++------
>> ? 1 file changed, 3 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
>> index 4ce9f00ae10e..5de21ad4bd05 100644
>> --- a/drivers/vhost/scsi.c
>> +++ b/drivers/vhost/scsi.c
>> @@ -1814,12 +1814,9 @@ static int vhost_scsi_open(struct inode *inode,
struct file *f)
>> ????? struct vhost_virtqueue **vqs;
>> ????? int r = -ENOMEM, i;
>> ? -??? vs = kzalloc(sizeof(*vs), GFP_KERNEL | __GFP_NOWARN |
__GFP_RETRY_MAYFAIL);
>> -??? if (!vs) {
>> -??????? vs = vzalloc(sizeof(*vs));
>> -??????? if (!vs)
>> -??????????? goto err_vs;
>> -??? }
>> +??? vs = kvzalloc(sizeof(*vs), GFP_KERNEL);
>> +??? if (!vs)
>> +??????? goto err_vs;
>> ? ????? vqs = kmalloc_array(VHOST_SCSI_MAX_VQ, sizeof(*vqs),
GFP_KERNEL);
>> ????? if (!vqs)
>
>
> Acked-by: Jason Wang <jasowang at redhat.com>
>
>
>