netdev - Re: [PATCH net-next v3 2/5] mm: add a signature in struct page

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Message-ID: <CALvZod7UUxTavexGCzbKaK41LAW7mkfQrnDhFbjo-KvH9P6KsQ@mail.gmail.com>
Date:   Sat, 10 Apr 2021 10:42:30 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Matteo Croce <mcroce@...ux.microsoft.com>,
        netdev <netdev@...r.kernel.org>, Linux MM <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>,
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        Andrew Lunn <andrew@...n.ch>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v3 2/5] mm: add a signature in struct page

On Sat, Apr 10, 2021 at 9:16 AM Ilias Apalodimas
<ilias.apalodimas@...aro.org> wrote:
>
> Hi Matthew
>
> On Sat, Apr 10, 2021 at 04:48:24PM +0100, Matthew Wilcox wrote:
> > On Sat, Apr 10, 2021 at 12:37:58AM +0200, Matteo Croce wrote:
> > > This is needed by the page_pool to avoid recycling a page not allocated
> > > via page_pool.
> >
> > Is the PageType mechanism more appropriate to your needs?  It wouldn't
> > be if you use page->_mapcount (ie mapping it to userspace).
>
> Interesting!
> Please keep in mind this was written ~2018 and was stale on my branches for
> quite some time.  So back then I did try to use PageType, but had not free
> bits.  Looking at it again though, it's cleaned up.  So yes I think this can
> be much much cleaner.  Should we go and define a new PG_pagepool?
>
>

Can this page_pool be used for TCP RX zerocopy? If yes then PageType
can not be used.

There is a recent discussion [1] on memcg accounting of TCP RX
zerocopy and I am wondering if this work can somehow help in that
regard. I will take a look at the series.

[1] https://lore.kernel.org/linux-mm/20210316013003.25271-1-arjunroy.kdev@gmail.com/