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

Dongli Zhang
2021-01-23T20:18:54Z

According to my "git send-email" history, I have CCed jasowang@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@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)
>