On 1/21/21 1:00 AM, Jason Wang wrote:

On 2021/1/21 13:03, Dongli Zhang wrote:

quoted

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 <redacted>
Cc: Joe Jin <redacted>
Signed-off-by: Dongli Zhang <redacted>
---
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)

Can we use kvzalloc?

Thank you very much for the suggestion.

To use 'GFP_NOWAIT' will avoid any direct compact in __alloc_pages_slowpath(),
while to use kvzalloc() will just avoid retrying direct compact for multiple times.

Although the latter will still do direct compact (without retry), I think it is
better than the former using GFP_NOWAIT.

I will send v2 with kvzalloc().

Thank you very much!

Dongli Zhang
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