Subject: Re: [net-next rfc 1/3] net: avoid high order memory allocation for queues by using flex array

From: Jason Wang <[email-masked]>
Date: Wed, 19 Jun 2013 15:14:52 +0800

On 06/19/2013 02:31 PM, Eric Dumazet wrote:
> On Wed, 2013-06-19 at 13:40 +0800, Jason Wang wrote:
>> Currently, we use kcalloc to allocate rx/tx queues for a net device which could
>> be easily lead to a high order memory allocation request when initializing a
>> multiqueue net device. We can simply avoid this by switching to use flex array
>> which always allocate at order zero.
>>
>> Signed-off-by: Jason Wang <[email-masked]>
>> ---
>>  include/linux/netdevice.h |   13 ++++++----
>>  net/core/dev.c            |   57 ++++++++++++++++++++++++++++++++------------
>>  net/core/net-sysfs.c      |   15 +++++++----
>>  3 files changed, 58 insertions(+), 27 deletions(-)
>>
>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>> index 09b4188..c0b5d04 100644
>> --- a/include/linux/netdevice.h
>> +++ b/include/linux/netdevice.h
>> @@ -32,6 +32,7 @@
>>  #include <linux/atomic.h>
>>  #include <asm/cache.h>
>>  #include <asm/byteorder.h>
>> +#include <linux/flex_array.h>
>>  
>>  #include <linux/percpu.h>
>>  #include <linux/rculist.h>
>> @@ -1230,7 +1231,7 @@ struct net_device {
>>  
>>
>>  #ifdef CONFIG_RPS
>> -	struct netdev_rx_queue	*_rx;
>> +	struct flex_array	*_rx;
>>  
>>  	/* Number of RX queues allocated at register_netdev() time */
>>  	unsigned int		num_rx_queues;
>> @@ -1250,7 +1251,7 @@ struct net_device {
>>  /*
>>   * Cache lines mostly used on transmit path
>>   */
>> -	struct netdev_queue	*_tx ____cacheline_aligned_in_smp;
>> +	struct flex_array	*_tx ____cacheline_aligned_in_smp;
>>  
> Using flex_array and adding overhead in this super critical part of
> network stack, only to avoid order-1 allocations done in GFP_KERNEL
> context is simply insane.

Yes, and I also miss the fact of GFP_KERNEL allocation.
> We can revisit this in 2050 if we ever need order-4 allocations or so,
> and still use 4K pages.
>
>

Will drop this patch, thanks.