linux-kernel - Re: [PATCH net-next v3 3/4] page_pool: introduce page_pool

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Date:   Fri, 16 Jun 2023 11:47:10 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     Alexander Duyck <alexander.duyck@...il.com>, brouer@...hat.com,
        Yunsheng Lin <linyunsheng@...wei.com>, davem@...emloft.net,
        pabeni@...hat.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Maryam Tahhan <mtahhan@...hat.com>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH net-next v3 3/4] page_pool: introduce page_pool_alloc()
 API

On Fri, 16 Jun 2023 20:41:45 +0200 Jesper Dangaard Brouer wrote:
> > This is a sort-of. One thing that has come up as of late is that all
> > this stuff is being moved over to folios anyway and getting away from
> > pages. In addition I am not sure how often we are having to take this
> > path as I am not sure how many non-Tx frames end up having to have
> > fragments added to them. For something like veth it might be more
> > common though since Tx becomes Rx in this case.  
> 
> I'm thinking, that is it very unlikely that XDP have modified the
> fragments.  So, why are we allocating and copying the fragments?
> Wouldn't it be possible for this veth code to bump the refcnt on these
> fragments? (maybe I missed some detail).

They may be page cache pages, AFAIU.