linux-kernel - Re: [PATCH 1/1] vhost scsi: allocate vhost_scsi with GFP

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Message-ID: <3aa5c6ca-abd3-13c4-b6a6-504f3a52bae7@redhat.com>
Date:   Thu, 21 Jan 2021 17:00:25 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, mst@...hat.com, pbonzini@...hat.com,
        stefanha@...hat.com, joe.jin@...cle.com,
        aruna.ramakrishna@...cle.com
Subject: Re: [PATCH 1/1] vhost scsi: allocate vhost_scsi with GFP_NOWAIT to
 avoid delay


On 2021/1/21 13:03, 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 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
> changes allocation to GFP_NOWAIT in order to avoid the delay caused by
> memory page compact.
>
> Cc: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
> Cc: Joe Jin <joe.jin@...cle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
> ---
> Another option is to rework by reducing the size of 'struct vhost_scsi',
> e.g., by replacing inline vhost_scsi.vqs with just memory pointers while
> each vhost_scsi.vqs[i] should be allocated separately. Please let me
> know if that option is better.
>
>   drivers/vhost/scsi.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> index 4ce9f00ae10e..85eaa4e883f4 100644
> --- a/drivers/vhost/scsi.c
> +++ b/drivers/vhost/scsi.c
> @@ -1814,7 +1814,7 @@ 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);
> +	vs = kzalloc(sizeof(*vs), GFP_NOWAIT | __GFP_NOWARN);
>   	if (!vs) {
>   		vs = vzalloc(sizeof(*vs));
>   		if (!vs)


Can we use kvzalloc?

Thanks