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

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Date:   Tue, 2 Feb 2021 15:56:18 +0100
From:   Pankaj Gupta <pankaj.gupta.linux@...il.com>
To:     Dongli Zhang <dongli.zhang@...cle.com>
Cc:     virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>, joe.jin@...cle.com,
        aruna.ramakrishna@...cle.com
Subject: Re: [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@...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)

 Acked-by: Pankaj Gupta <pankaj.gupta@...ud.ionos.com>