linux-kernel - Re: [PATCH net-next v5 03/14] page_pool: avoid calling no-op externals when possible

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Message-ID: <20231127101720.282862f6@kernel.org>
Date:   Mon, 27 Nov 2023 10:17:20 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     Yunsheng Lin <linyunsheng@...wei.com>,
        Christoph Hellwig <hch@....de>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Michal Kubiak <michal.kubiak@...el.com>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        Alexander Duyck <alexanderduyck@...com>,
        David Christensen <drc@...ux.vnet.ibm.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        "Ilias Apalodimas" <ilias.apalodimas@...aro.org>,
        Paul Menzel <pmenzel@...gen.mpg.de>, <netdev@...r.kernel.org>,
        <intel-wired-lan@...ts.osuosl.org>, <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v5 03/14] page_pool: avoid calling no-op
 externals when possible

On Mon, 27 Nov 2023 15:32:19 +0100 Alexander Lobakin wrote:
> > Sorry for not remembering the suggestion:(  
> 
> In the previous versions of this change I used a global flag per whole
> page_pool, just like XSk does for the whole XSk buff pool, then you
> proposed to use the lowest bit of ::dma_addr and store it per page, so
> that it would be more granular/precise. I tested it and it doesn't
> perform worse than global, but in some cases may be beneficial.

FWIW I'd vote to stick to per-page pool. You seem to handle the
sizeof(dma_addr_t) > sizeof(long) case correctly but the code is
growing in complexity, providing no known/measurable benefit.
We can always do this later but for now it seems like a premature
optimization to me.