Subject: Re: 2.6.1[78] page allocation failure. order:3, mode:0x20

From: Auke Kok <[email-masked]>
Date: Sun, 24 Sep 2006 14:15:42 -0700

Evgeniy Polyakov wrote:
> On Fri, Sep 22, 2006 at 10:33:48PM -0700, Andrew Morton ([email-masked]) wrote:
>>> The NET_IP_ALIGN existed not just for fun :)  There are ramifications
>>> for removing it.
>> It's still there, isn't it?
>>
>> For the 9k MTU case, for example, we end up allocating 16384 byte skbs
>> instead of 32786 kbytes ones.
> 
> This patch will not help - netdev_alloc_skb() adds additional
> NET_SKB_PAD and then alloc_skb() adds sizeof(struct skb_shared_info).
> And even if you acconut for them in adapter->rx_buf_len, chip still can
> overwrite that area (in the thread mentioned in this e-mail thread
> before I posted such patch and received a dump of sizes chip receives -
> there were a lot of _different_ ones which were too close to the limit).

I just did the math on it and it does not compute as I wanted too, we're 
basically flowing to the next larger buffersize 2 mtu bytes earlier, undoing 
any benefit completely.

There is not much that can fix this issue since the hardware will always 
receive in 2-order buffers and dma that back in its entirity, so we must always 
claim size for NET_IP_ALIGN and NET_SKB_PAD after the 2-order bufsz. For the 
9kb mtu case (16kb hw bufsz), we're stuck with 32kb slab allocations. bummer.

Andrew, please drop this patch.

Auke

> 
>> diff -puN drivers/net/e1000/e1000_main.c~e1000-account-for-net_ip_align-when-calculating-bufsiz drivers/net/e1000/e1000_main.c
>> --- a/drivers/net/e1000/e1000_main.c~e1000-account-for-net_ip_align-when-calculating-bufsiz
>> +++ a/drivers/net/e1000/e1000_main.c
>> @@ -1101,7 +1101,7 @@ e1000_sw_init(struct e1000_adapter *adap
>>  
>>  	pci_read_config_word(pdev, PCI_COMMAND, &hw->pci_cmd_word);
>>  
>> -	adapter->rx_buffer_len = MAXIMUM_ETHERNET_VLAN_SIZE;
>> +	adapter->rx_buffer_len = MAXIMUM_ETHERNET_VLAN_SIZE + NET_IP_ALIGN;
>>  	adapter->rx_ps_bsize0 = E1000_RXBUFFER_128;
>>  	hw->max_frame_size = netdev->mtu +
>>  			     ENET_HEADER_SIZE + ETHERNET_FCS_SIZE;
>> @@ -3163,26 +3163,27 @@ e1000_change_mtu(struct net_device *netd
>>  	 * larger slab size
>>  	 * i.e. RXBUFFER_2048 --> size-4096 slab */
>>  
>> -	if (max_frame <= E1000_RXBUFFER_256)
>> +	if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_256)
>>  		adapter->rx_buffer_len = E1000_RXBUFFER_256;
>> -	else if (max_frame <= E1000_RXBUFFER_512)
>> +	else if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_512)
>>  		adapter->rx_buffer_len = E1000_RXBUFFER_512;
>> -	else if (max_frame <= E1000_RXBUFFER_1024)
>> +	else if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_1024)
>>  		adapter->rx_buffer_len = E1000_RXBUFFER_1024;
>> -	else if (max_frame <= E1000_RXBUFFER_2048)
>> +	else if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_2048)
>>  		adapter->rx_buffer_len = E1000_RXBUFFER_2048;
>> -	else if (max_frame <= E1000_RXBUFFER_4096)
>> +	else if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_4096)
>>  		adapter->rx_buffer_len = E1000_RXBUFFER_4096;
>> -	else if (max_frame <= E1000_RXBUFFER_8192)
>> +	else if (max_frame + NET_IP_ALIGN <= E1000_RXBUFFER_8192)
>>  		adapter->rx_buffer_len = E1000_RXBUFFER_8192;
>> -	else if (max_frame <= E1000_RXBUFFER_16384)
>> +	else
>>  		adapter->rx_buffer_len = E1000_RXBUFFER_16384;
>>  
>>  	/* adjust allocation if LPE protects us, and we aren't using SBP */
>>  	if (!adapter->hw.tbi_compatibility_on &&
>>  	    ((max_frame == MAXIMUM_ETHERNET_FRAME_SIZE) ||
>>  	     (max_frame == MAXIMUM_ETHERNET_VLAN_SIZE)))
>> -		adapter->rx_buffer_len = MAXIMUM_ETHERNET_VLAN_SIZE;
>> +		adapter->rx_buffer_len = MAXIMUM_ETHERNET_VLAN_SIZE +
>> +					NET_IP_ALIGN;
>>  
>>  	netdev->mtu = new_mtu;
>>  
>> @@ -4002,7 +4003,8 @@ e1000_alloc_rx_buffers(struct e1000_adap
>>  	struct e1000_buffer *buffer_info;
>>  	struct sk_buff *skb;
>>  	unsigned int i;
>> -	unsigned int bufsz = adapter->rx_buffer_len + NET_IP_ALIGN;
>> +	/* we have already accounted for NET_IP_ALIGN */
>> +	unsigned int bufsz = adapter->rx_buffer_len;
>>  
>>  	i = rx_ring->next_to_use;
>>  	buffer_info = &rx_ring->buffer_info[i];
>> _
>>
>> -
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>