From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [PATCH 3.10] vhost-net: backport extend device allocation to 3.10
Date: Sun, 12 Oct 2014 12:30:25 +0300
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Cc: kvm@vger.kernel.org, Eddie Chapman <eddie@ehuk.net>,
	Michael Mueller <mimu@linux.vnet.ibm.com>,
	Romain Francoise <romain@orebokech.com>
To: Dmitry Petuhov <mityapetuhov@gmail.com>
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On Thu, Oct 09, 2014 at 08:41:23AM +0400, Dmitry Petuhov wrote:
> From: Michael S. Tsirkin <mst@redhat.com>
> 
> upstream commit 23cc5a991c7a9fb7e6d6550e65cee4f4173111c5
> 
> Michael Mueller provided a patch to reduce the size of
> vhost-net structure as some allocations could fail under
> memory pressure/fragmentation. We are still left with
> high order allocations though.
> 
> This patch is handling the problem at the core level, allowing
> vhost structures to use vmalloc() if kmalloc() failed.
> 
> As vmalloc() adds overhead on a critical network path, add __GFP_REPEAT
> to kzalloc() flags to do this fallback only when really needed.
> 
> People are still looking at cleaner ways to handle the problem
> at the API level, probably passing in multiple iovecs.
> This hack seems consistent with approaches
> taken since then by drivers/vhost/scsi.c and net/core/dev.c
> 
> Based on patch by Romain Francoise.
> 
> Cc: Michael Mueller <mimu@linux.vnet.ibm.com>
> Signed-off-by: Romain Francoise <romain@orebokech.com>
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> [mityapetuhov: backport to v3.10: vhost_net_free() in one more place]
> Signed-off-by: Dmitry Petuhov <mityapetuhov@gmail.com>

Sounds reasonable.

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
> diff -uprN a/drivers/vhost/net.c b/drivers/vhost/net.c
> --- a/drivers/vhost/net.c	2014-10-09 06:45:08.336283258 +0400
> +++ b/drivers/vhost/net.c	2014-10-09 06:51:21.796266607 +0400
> @@ -18,6 +18,7 @@
>  #include <linux/rcupdate.h>
>  #include <linux/file.h>
>  #include <linux/slab.h>
> +#include <linux/vmalloc.h>
>  
>  #include <linux/net.h>
>  #include <linux/if_packet.h>
> @@ -707,18 +708,30 @@ static void handle_rx_net(struct vhost_w
>  	handle_rx(net);
>  }
>  
> +static void vhost_net_free(void *addr)
> +{
> +	if (is_vmalloc_addr(addr))
> +		vfree(addr);
> +	else
> +		kfree(addr);
> +}
> +
>  static int vhost_net_open(struct inode *inode, struct file *f)
>  {
> -	struct vhost_net *n = kmalloc(sizeof *n, GFP_KERNEL);
> +	struct vhost_net *n;
>  	struct vhost_dev *dev;
>  	struct vhost_virtqueue **vqs;
>  	int r, i;
>  
> -	if (!n)
> -		return -ENOMEM;
> +	n = kmalloc(sizeof *n, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
> +	if (!n) {
> +		n = vmalloc(sizeof *n);
> +		if (!n)
> +			return -ENOMEM;
> +	}
>  	vqs = kmalloc(VHOST_NET_VQ_MAX * sizeof(*vqs), GFP_KERNEL);
>  	if (!vqs) {
> -		kfree(n);
> +		vhost_net_free(n);
>  		return -ENOMEM;
>  	}
>  
> @@ -737,7 +750,7 @@ static int vhost_net_open(struct inode *
>  	}
>  	r = vhost_dev_init(dev, vqs, VHOST_NET_VQ_MAX);
>  	if (r < 0) {
> -		kfree(n);
> +		vhost_net_free(n);
>  		kfree(vqs);
>  		return r;
>  	}
> @@ -840,7 +853,7 @@ static int vhost_net_release(struct inod
>  	 * since jobs can re-queue themselves. */
>  	vhost_net_flush(n);
>  	kfree(n->dev.vqs);
> -	kfree(n);
> +	vhost_net_free(n);
>  	return 0;
>  }
>