linux-kernel - [PATCH 1/1] vhost scsi: allocate vhost_scsi with GFP

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Date:   Wed, 20 Jan 2021 21:03:28 -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 1/1] vhost scsi: allocate vhost_scsi with GFP_NOWAIT 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 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@...cle.com>
Cc: Joe Jin <joe.jin@...cle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@...cle.com>
---
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)
-- 
2.17.1