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

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Message-ID: <20230221091458.7d026652@kernel.org>
Date:   Tue, 21 Feb 2023 09:14:58 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.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 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.