netdev - Re: [PATCH net-next v2 1/4] net: Register system page pool as an XDP memory model

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Date: Thu, 4 Apr 2024 11:08:14 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: John Fastabend <john.fastabend@...il.com>,
	Toke Høiland-Jørgensen <toke@...hat.com>, "David S.
 Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, "Jakub
 Kicinski" <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, "Alexei
 Starovoitov" <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
	"Jesper Dangaard Brouer" <hawk@...nel.org>
CC: <netdev@...r.kernel.org>, <bpf@...r.kernel.org>
Subject: Re: [PATCH net-next v2 1/4] net: Register system page pool as an XDP
 memory model

From: John Fastabend <john.fastabend@...il.com>
Date: Wed, 03 Apr 2024 13:20:32 -0700

> Toke Høiland-Jørgensen wrote:
>> To make the system page pool usable as a source for allocating XDP
>> frames, we need to register it with xdp_reg_mem_model(), so that page
>> return works correctly. This is done in preparation for using the system
>> page pool for the XDP live frame mode in BPF_TEST_RUN; for the same
>> reason, make the per-cpu variable non-static so we can access it from
>> the test_run code as well.
>>
>> Reviewed-by: Alexander Lobakin <aleksander.lobakin@...el.com>
>> Tested-by: Alexander Lobakin <aleksander.lobakin@...el.com>
>> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
>> ---
>>  include/linux/netdevice.h |  1 +
>>  net/core/dev.c            | 13 ++++++++++++-
>>  2 files changed, 13 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
>> index c541550b0e6e..e1dfdf0c4075 100644
>> --- a/include/linux/netdevice.h
>> +++ b/include/linux/netdevice.h
>> @@ -3345,6 +3345,7 @@ static inline void input_queue_tail_incr_save(struct softnet_data *sd,
>>  }
>>  
>>  DECLARE_PER_CPU_ALIGNED(struct softnet_data, softnet_data);
>> +DECLARE_PER_CPU_ALIGNED(struct page_pool *, system_page_pool);
>>  
>>  static inline int dev_recursion_level(void)
>>  {
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index d8dd293a7a27..cdb916a647e7 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -428,7 +428,7 @@ EXPORT_PER_CPU_SYMBOL(softnet_data);
>>   * PP consumers must pay attention to run APIs in the appropriate context
>>   * (e.g. NAPI context).
>>   */
>> -static DEFINE_PER_CPU_ALIGNED(struct page_pool *, system_page_pool);
>> +DEFINE_PER_CPU_ALIGNED(struct page_pool *, system_page_pool);
>>  
>>  #ifdef CONFIG_LOCKDEP
>>  /*
>> @@ -11739,12 +11739,20 @@ static int net_page_pool_create(int cpuid)
>>  		.pool_size = SYSTEM_PERCPU_PAGE_POOL_SIZE,
>>  		.nid = NUMA_NO_NODE,
>>  	};
>> +	struct xdp_mem_info info;
>>  	struct page_pool *pp_ptr;
>> +	int err;
>>  
>>  	pp_ptr = page_pool_create_percpu(&page_pool_params, cpuid);
>>  	if (IS_ERR(pp_ptr))
>>  		return -ENOMEM;
>>  
>> +	err = xdp_reg_mem_model(&info, MEM_TYPE_PAGE_POOL, pp_ptr);
>> +	if (err) {
>> +		page_pool_destroy(pp_ptr);
>> +		return err;
>> +	}
>> +
>>  	per_cpu(system_page_pool, cpuid) = pp_ptr;
>>  #endif
>>  	return 0;
>> @@ -11834,12 +11842,15 @@ static int __init net_dev_init(void)
>>  out:
>>  	if (rc < 0) {
>>  		for_each_possible_cpu(i) {
>> +			struct xdp_mem_info mem = { .type = MEM_TYPE_PAGE_POOL };
>>  			struct page_pool *pp_ptr;
>>  
>>  			pp_ptr = per_cpu(system_page_pool, i);
>>  			if (!pp_ptr)
>>  				continue;
>>  
>> +			mem.id = pp_ptr->xdp_mem_id;
>> +			xdp_unreg_mem_model(&mem);
> 
> Take it or leave it, a net_page_pool_destroy(int cpuid) would be
> symmetric here.
> 
>>  			page_pool_destroy(pp_ptr);

I believe it's better to remove this page_pool_destroy() and let
xdp_unreg_mem_model() destroy it.

>>  			per_cpu(system_page_pool, i) = NULL;
>>  		}
> 
> Acked-by: John Fastabend <john.fastabend@...il.com>

Thanks,
Olek