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Subject: Re: [PATCH v2 1/1] vhost scsi: alloc vhost_scsi with kvzalloc() to
 avoid delay
To:     Dongli Zhang <dongli.zhang@oracle.com>,
        virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
        netdev@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, mst@redhat.com, pbonzini@redhat.com,
        stefanha@redhat.com, joe.jin@oracle.com,
        aruna.ramakrishna@oracle.com
References: <20210123080853.4214-1-dongli.zhang@oracle.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <61ed58d6-052b-9065-361d-dc6010fc91ef@redhat.com>
Date:   Mon, 25 Jan 2021 11:12:07 +0800
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On 2021/1/23 下午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@oracle.com>
> Cc: Joe Jin <joe.jin@oracle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@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@redhat.com>