netdev - Re: [PATCH v2 1/1] vhost scsi: alloc vhost_scsi with kvzalloc() to avoid delay

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Message-ID: <b85fb58d-72b4-2c0a-a412-3dbdb437e042@oracle.com>
Date:   Sat, 23 Jan 2021 12:14:34 -0800
From:   Dongli Zhang <dongli.zhang@...cle.com>
To:     virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     aruna.ramakrishna@...cle.com, mst@...hat.com, joe.jin@...cle.com,
        linux-kernel@...r.kernel.org, stefanha@...hat.com,
        pbonzini@...hat.com, Jason Wang <jasowang@...hat.com>
Subject: Re: [PATCH v2 1/1] vhost scsi: alloc vhost_scsi with kvzalloc() to
 avoid delay

According to my "git send-email" history, I have CCed jasowang@...hat.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@...cle.com>
> Cc: Joe Jin <joe.jin@...cle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.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)
>