Re: [PATCH] vhost-net: fall back to vmalloc if high-order allocation fails

On Friday, January 25, 2013 03:03:13 AM Cong Wang wrote:

["Followup-To:" header set to gmane.linux.network.]

On Wed, 23 Jan 2013 at 20:46 GMT, Romain Francoise [off-list ref] 

wrote:

quoted

Creating a vhost-net device allocates an object large enough (34320 bytes
on x86-64) to trigger an order-4 allocation, which may fail if memory if

fragmented:
 libvirtd: page allocation failure: order:4, mode:0x2000d0
 ...
 SLAB: Unable to allocate memory on node 0 (gfp=0xd0)
 
   cache: size-65536, object size: 65536, order: 4
   node 0: slabs: 8/8, objs: 8/8, free: 0

In that situation, rather than forcing the caller to use regular
virtio-net, try to allocate the descriptor with vmalloc().

The real problem is vhost_net struct is really big, it
should be reduced rather than workarounded like this.

Looks like iov in vhost_virtqueue is a little big:

    struct iovec iov[UIO_MAXIOV];

Maybe we can use pointer and allocate it like indirect in 
vhost_dev_alloc_iovecs().

quoted

+static void vhost_net_kvfree(void *addr)
+{
+	if (is_vmalloc_addr(addr))
+		vfree(addr);
+	else
+		kfree(addr);
+}
+

This kind of stuff should really go to mm, not netdev.

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