linux-kernel - Re: [PATCH v3] page_pool: add a comment explaining the fragment counter usage

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Message-ID: <CAC_iWjJO6-C+v5dRHxqvpCy_miwhG7g6J2=o8YzfumfMHiKZ0Q@mail.gmail.com>
Date:   Tue, 21 Feb 2023 19:21:58 +0200
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, alexander.duyck@...il.com,
        Alexander Duyck <alexanderduyck@...com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] page_pool: add a comment explaining the fragment
 counter usage

On Tue, 21 Feb 2023 at 19:15, Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Sat, 18 Feb 2023 00:21:30 +0200 Ilias Apalodimas wrote:
> > When reading the page_pool code the first impression is that keeping
> > two separate counters, one being the page refcnt and the other being
> > fragment pp_frag_count, is counter-intuitive.
> >
> > However without that fragment counter we don't know when to reliably
> > destroy or sync the outstanding DMA mappings.  So let's add a comment
> > explaining this part.
>
> I discussed with Paolo off-list, since it's just a comment change
> I'll push it in.

Fair enough. Thanks Jakub.

Regards
/Ilias