netdev - Re: [PATCH net-next v6 3/5] page_pool: Allow drivers to hint on SKB recycling

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Date:   Mon, 7 Jun 2021 07:38:43 +0300
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Tariq Toukan <ttoukan.linux@...il.com>
Cc:     Matteo Croce <mcroce@...ux.microsoft.com>,
        David Ahern <dsahern@...il.com>,
        Yunsheng Lin <linyunsheng@...wei.com>, netdev@...r.kernel.org,
        linux-mm@...ck.org, Ayush Sawal <ayush.sawal@...lsio.com>,
        Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
        Rohit Maheshwari <rohitm@...lsio.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Russell King <linux@...linux.org.uk>,
        Mirko Lindner <mlindner@...vell.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Tariq Toukan <tariqt@...dia.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Boris Pismenny <borisp@...dia.com>,
        Arnd Bergmann <arnd@...db.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>, Yu Zhao <yuzhao@...gle.com>,
        Will Deacon <will@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Roman Gushchin <guro@...com>, Hugh Dickins <hughd@...gle.com>,
        Peter Xu <peterx@...hat.com>, Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Alexander Lobakin <alobakin@...me>,
        Cong Wang <cong.wang@...edance.com>, wenxu <wenxu@...oud.cn>,
        Kevin Hao <haokexin@...il.com>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Marco Elver <elver@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Guillaume Nault <gnault@...hat.com>,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        bpf@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Saeed Mahameed <saeedm@...dia.com>,
        Andrew Lunn <andrew@...n.ch>, Paolo Abeni <pabeni@...hat.com>,
        Sven Auhagen <sven.auhagen@...eatech.de>
Subject: Re: [PATCH net-next v6 3/5] page_pool: Allow drivers to hint on SKB
 recycling

Hi Tariq,

> > > > 
> > > > Yes the comment is there to prohibit people (mlx5 only actually) to add the
> > > > recycling bit on their driver.  Because if they do it will *probably* work
> > > > but they might get random corrupted packets which will be hard to debug.
> > > > 
> > > 
> > > What's the complexity for getting it to work with split page model?
> > > Since 1500 is the default MTU, requiring a page per packet means a lot
> > > of wasted memory.
> > 
> > We could create a new memory model, e.g. MEM_TYPE_PAGE_SPLIT, and
> > restore the behavior present in the previous versions of this serie,
> > which is, save xdp_mem_info in struct page.
> > As this could slightly impact the performances, this can be added in a
> > future change when the drivers which are doing it want to use this
> > recycling api.
> > 
> 
> page-split model doesn't only help reduce memory waste, but increase
> cache-locality, especially for aggregated GRO SKBs.
> 
> I'm looking forward to integrating the page-pool SKB recycling API into
> mlx5e datapath. For this we need it to support the page-split model.
> 
> Let's see what's missing and how we can help making this happen.

Yes that's the final goal.  As I said I don't think adding the page split
model will fundamentally change the current patchset.  So imho we should
get this in first, make sure that everything is fine, and then add code for
the mlx cards.

Regards
/Ilias