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Date:   Mon, 27 Nov 2023 10:17:20 -0800
From:   Jakub Kicinski <kuba@kernel.org>
To:     Alexander Lobakin <aleksander.lobakin@intel.com>
Cc:     Yunsheng Lin <linyunsheng@huawei.com>,
        Christoph Hellwig <hch@lst.de>,
        Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
        Michal Kubiak <michal.kubiak@intel.com>,
        Larysa Zaremba <larysa.zaremba@intel.com>,
        Alexander Duyck <alexanderduyck@fb.com>,
        David Christensen <drc@linux.vnet.ibm.com>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        "Ilias Apalodimas" <ilias.apalodimas@linaro.org>,
        Paul Menzel <pmenzel@molgen.mpg.de>, <netdev@vger.kernel.org>,
        <intel-wired-lan@lists.osuosl.org>, <linux-kernel@vger.kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>
Subject: Re: [PATCH net-next v5 03/14] page_pool: avoid calling no-op
 externals when possible
Message-ID: <20231127101720.282862f6@kernel.org>
In-Reply-To: <a1a0c27f-f367-40e7-9dc2-9421b4b6379a@intel.com>
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        <20231124154732.1623518-4-aleksander.lobakin@intel.com>
        <6bd14aa9-fa65-e4f6-579c-3a1064b2a382@huawei.com>
        <a1a0c27f-f367-40e7-9dc2-9421b4b6379a@intel.com>
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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.