linux-kernel - Re: [PATCH net-next 08/11] iavf: switch to Page Pool

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Date:   Fri, 2 Jun 2023 15:25:01 +0200
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     David Christensen <drc@...ux.vnet.ibm.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Michal Kubiak <michal.kubiak@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        "Jesper Dangaard Brouer" <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Christoph Hellwig <hch@....de>, <netdev@...r.kernel.org>,
        <intel-wired-lan@...ts.osuosl.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 08/11] iavf: switch to Page Pool

From: David Christensen <drc@...ux.vnet.ibm.com>
Date: Wed, 31 May 2023 13:18:59 -0700

> 
> 
> On 5/25/23 4:08 AM, Alexander Lobakin wrote:
>>> Any plans to add page pool fragmentation support (i.e.
>>> PP_FLAG_PAGE_FRAG) in the future to better support architectures with
>>> larger page sizes such as 64KB on ppc64le?
>>
>> Currently no, we resigned from page fragmentation due to the complexity
>> and restrictions it provides for no benefits on x86_64. But I remember
>> that pages > 4 Kb exist (I have a couple MIPS boards where I have fun
>> sometimes and page size is set to 16 Kb there. But still always use 1
>> page per frame).
>> By "better support" you mean reducing memory usage or something else?
> 
> Yes, reducing memory waste.  Current generation P10 systems default to
> quad-port, 10Gb copper i40e NICs.  When you combine a large number of
> CPUs, and therefore a large number of RX queues, with a 64KB page
> allocation per packet, memory usage can balloon very quickly as you add
> additional ports.

Yeah, I got it. Unfortunately, page split adds a bunch of overhead for
no benefit on 4k systems. There's a small series here on netdev which
tries to combine frag and non-frag allocations in Page Pool, so that
there will be no overhead on 4k systems and no memory waste on 8k+ ones.

> 
> Would you be open to patches to address this further down the road as
> your refactoring effort gets closer to completion?

Let's see how the abovementioned effort goes. I feel like a generic
solution would be better than trying to handle that per-driver.

> 
> Dave

Thanks,
Olek