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

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Date:   Sat, 23 Jan 2021 00:08:53 -0800
From:   Dongli Zhang <dongli.zhang@...cle.com>
To:     virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, mst@...hat.com, jasowang@...hat.com,
        pbonzini@...hat.com, stefanha@...hat.com, joe.jin@...cle.com,
        aruna.ramakrishna@...cle.com
Subject: [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)
-- 
2.17.1