Re: [pbs-devel] [PATCH proxmox-backup-restore-image 4/4] add workaround kernel patch for vsock panics

[Dietmar Maurer <dietmar@proxmox.com>]

Such small buffer sizes can reduce performance. I usually go
for a minimum of 256K.

So do we really need this?

What is a 128 MiB RAM machine???


> On 04/26/2021 3:04 PM Stefan Reiter <s.reiter@proxmox.com> wrote:
> 
>  
> Allocation failures for vsock packet buffers occur routinely when
> downloading more than one stream at the same time, with less then 512
> MiB of RAM it sometimes even occurs for single downloads.
> 
> This appears to fix it in all of my reproducer scenarios, tested with up
> to 6 downloads at once in a 128 MiB RAM machine.
> 
> Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
> ---
>  .../0003-vsock-reduce-packet-size.patch       | 36 +++++++++++++++++++
>  1 file changed, 36 insertions(+)
>  create mode 100644 src/patches/kernel/0003-vsock-reduce-packet-size.patch
> 
> diff --git a/src/patches/kernel/0003-vsock-reduce-packet-size.patch b/src/patches/kernel/0003-vsock-reduce-packet-size.patch
> new file mode 100644
> index 0000000..378da53
> --- /dev/null
> +++ b/src/patches/kernel/0003-vsock-reduce-packet-size.patch
> @@ -0,0 +1,36 @@
> +From a437d428733881f408b5d42eb75812600083cb75 Mon Sep 17 00:00:00 2001
> +From: Stefan Reiter <s.reiter@proxmox.com>
> +Date: Mon, 26 Apr 2021 14:08:36 +0200
> +Subject: [PATCH] vsock: reduce packet size
> +
> +Reduce the maximum packet size to avoid allocation errors in VMs with
> +very little memory available (since the buffer needs a contiguous
> +block of memory, which can get rare for 64kB blocks).
> +
> +4kB used to be the default, and according to [0] increasing it makes
> +the difference between ~25Gb/s and ~40Gb/s - certainly a lot faster,
> +but both within the realm of unreachable for our restore scenario.
> +
> +[0] https://stefano-garzarella.github.io/posts/2019-11-08-kvmforum-2019-vsock/
> +
> +Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
> +---
> + include/linux/virtio_vsock.h | 2 +-
> + 1 file changed, 1 insertion(+), 1 deletion(-)
> +
> +diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
> +index dc636b727179..18c09ff72929 100644
> +--- a/include/linux/virtio_vsock.h
> ++++ b/include/linux/virtio_vsock.h
> +@@ -9,7 +9,7 @@
> + 
> + #define VIRTIO_VSOCK_DEFAULT_RX_BUF_SIZE	(1024 * 4)
> + #define VIRTIO_VSOCK_MAX_BUF_SIZE		0xFFFFFFFFUL
> +-#define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		(1024 * 64)
> ++#define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE		(1024 * 4)
> + 
> + enum {
> + 	VSOCK_VQ_RX     = 0, /* for host to guest data */
> +-- 
> +2.20.1
> +
> -- 
> 2.20.1
> 
> 
> 
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