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Date:   Wed, 11 Dec 2019 11:06:32 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        "brouer@...hat.com" <brouer@...hat.com>
CC:     "jonathan.lemon@...il.com" <jonathan.lemon@...il.com>,
        "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org>,
        Li Rongqing <lirongqing@...du.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH][v2] page_pool: handle page recycle for NUMA_NO_NODE
 condition

On 2019/12/11 11:01, Yunsheng Lin wrote:
> On 2019/12/11 3:45, Saeed Mahameed wrote:
>>>> maybe assume that __page_pool_recycle_direct() is always called
>>>> from
>>>> the right node and change the current bogus check:
>>>>
>>>> from:
>>>> page_to_nid(page) == pool->p.nid 
>>>>
>>>> to:
>>>> page_to_nid(page) == numa_mem_id()
>>>>
>>>> This will allow recycling only if handling node is the same as
>>>> where
>>>> the page was allocated, regardless of pool->p.nid.
>>>>
>>>> so semantics are:
>>>>
>>>> 1) allocate from: pool->p.nid, as chosen by user.
>>>> 2) recycle when: page_to_nid(page) == numa_mem_id().
>>>> 3) pool user must guarantee that the handler will run on the right
>>>> node. which should always be the case. otherwise recycling will be
>>>> skipped (no cross numa recycling).
>>>>
>>>>
>>>> a) if the pool migrates, we will stop recycling until the pool
>>>> moves
>>>> back to original node, or user calls pool_update_nid() as we do in
>>>> mlx5.
>>>> b) if pool is NUMA_NO_NODE, then allocation and handling will be
>>>> done
>>>> on numa_mem_id(), which means the above check will work.
>>>
>>> Only checking page_to_nid(page) == numa_mem_id() may not work for the
>>> below
>>> case in mvneta.c:
>>>
>>> static int mvneta_create_page_pool(struct mvneta_port *pp,
>>> 				   struct mvneta_rx_queue *rxq, int
>>> size)
>>> {
>>> 	struct bpf_prog *xdp_prog = READ_ONCE(pp->xdp_prog);
>>> 	struct page_pool_params pp_params = {
>>> 		.order = 0,
>>> 		.flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV,
>>> 		.pool_size = size,
>>> 		.nid = cpu_to_node(0),
>>> 		.dev = pp->dev->dev.parent,
>>> 		.dma_dir = xdp_prog ? DMA_BIDIRECTIONAL :
>>> DMA_FROM_DEVICE,
>>> 		.offset = pp->rx_offset_correction,
>>> 		.max_len = MVNETA_MAX_RX_BUF_SIZE,
>>> 	};
>>>
>>> the pool->p.nid is not NUMA_NO_NODE, then the node of page allocated
>>> for rx
>>> may not be numa_mem_id() when running in the NAPI polling, because
>>> pool->p.nid
>>> is not the same as the node of cpu running in the NAPI polling.
>>>
>>> Does the page pool support recycling for above case?
>>>
>>
>> I don't think you want to allow cross numa recycling.
> 
> Cross numa recycling is not what I want.
> 
>>
>>> Or we "fix' the above case by setting pool->p.nid to
>>> NUMA_NO_NODE/dev_to_node(),
>>> or by calling pool_update_nid() in NAPI polling as mlx5 does?
>>>
>>
>> Yes just update_nid when needed, and make sure the NAPI polling runs on
>> a consistent core and eventually alloc/recycling will happen on the
>> same core.
> 
> To me, passing NUMA_NO_NODE/dev_to_node() seems to always work.
> Calling pool_update_nid() in NAPI polling is another way of passing
> NUMA_NO_NODE to page_pool_init().
> 
> And it seems it is a copy & paste problem for mvneta and netsec
> driver that uses cpu_to_node(0) as pool->p.nid but does not call
> page_pool_nid_changed() in the NAPI polling as mlx5 does.
> 
> So I suggest to remove page_pool_nid_changed() and always use
> NUMA_NO_NODE/dev_to_node() as pool->p.nid or make it clear (
> by comment or warning?)that page_pool_nid_changed() should be
> called when pool->p.nid is NUMA_NO_NODE/dev_to_node().
                          ~~

sorry for the typo.

I meant pool->p.nid is not NUMA_NO_NODE/dev_to_node().

> 
> I prefer to remove page_pool_nid_changed() if we do not allow
> cross numa recycling.
> 
> 
>>
>>>
>>>> Thanks,
>>>> Saeed.
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
> 
> 
> .
> 

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