[PATCH 1/1] vhost scsi: allocate vhost_scsi with GFP_NOWAIT to avoid delay

From: Dongli Zhang
Date: Thu Jan 21 2021 - 00:08:47 EST

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@xxxxxxxxxx>
Cc: Joe Jin <joe.jin@xxxxxxxxxx>
Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
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)