Re: [PATCH RFC 0/7] add socket to netdev page frag recycling support

[Yunsheng Lin]

On 2021/8/18 16:57, Eric Dumazet wrote:
> On Wed, Aug 18, 2021 at 5:33 AM Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote:
>>
>> This patchset adds the socket to netdev page frag recycling
>> support based on the busy polling and page pool infrastructure.
> 
> I really do not see how this can scale to thousands of sockets.
> 
> tcp_mem[] defaults to ~ 9 % of physical memory.
> 
> If you now run tests with thousands of sockets, their skbs will
> consume Gigabytes
> of memory on typical servers, now backed by order-0 pages (instead of
> current order-3 pages)
> So IOMMU costs will actually be much bigger.

As the page allocator support bulk allocating now, see:
https://elixir.bootlin.com/linux/latest/source/net/core/page_pool.c#L252

if the DMA also support batch mapping/unmapping, maybe having a
small-sized page pool for thousands of sockets may not be a problem?
Christoph Hellwig mentioned the batch DMA operation support in below
thread:
https://www.spinics.net/lists/netdev/msg666715.html

if the batched DMA operation is supported, maybe having the
page pool is mainly benefit the case of small number of socket?

> 
> Are we planning to use Gigabyte sized page pools for NIC ?
> 
> Have you tried instead to make TCP frags twice bigger ?

Not yet.

> This would require less IOMMU mappings.
> (Note: This could require some mm help, since PAGE_ALLOC_COSTLY_ORDER
> is currently 3, not 4)

I am not familiar with mm yet, but I will take a look about that:)

> 
> diff --git a/net/core/sock.c b/net/core/sock.c
> index a3eea6e0b30a7d43793f567ffa526092c03e3546..6b66b51b61be9f198f6f1c4a3d81b57fa327986a
> 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2560,7 +2560,7 @@ static void sk_leave_memory_pressure(struct sock *sk)
>         }
>  }
> 
> -#define SKB_FRAG_PAGE_ORDER    get_order(32768)
> +#define SKB_FRAG_PAGE_ORDER    get_order(65536)
>  DEFINE_STATIC_KEY_FALSE(net_high_order_alloc_disable_key);
> 
>  /**
> 
> 
> 
>>