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

From: Dongli Zhang
Date: Sat Jan 23 2021 - 03:08:00 EST

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