linux-kernel - Re: [PATCH v2] net: ethernet: mtk_eth_soc: fix misuse of mem alloc interface netdev[napi]_alloc

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Date:   Fri, 3 Jun 2022 08:25:22 -0700
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Chen Lin <chen45464546@....com>
Cc:     Felix Fietkau <nbd@....name>, Jakub Kicinski <kuba@...nel.org>,
        John Crispin <john@...ozen.org>,
        Sean Wang <sean.wang@...iatek.com>, Mark-MC.Lee@...iatek.com,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, matthias.bgg@...il.com,
        Netdev <netdev@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] net: ethernet: mtk_eth_soc: fix misuse of mem alloc
 interface netdev[napi]_alloc_frag

On Fri, Jun 3, 2022 at 2:03 AM Chen Lin <chen45464546@....com> wrote:
>
> When rx_flag == MTK_RX_FLAGS_HWLRO,
> rx_data_len = MTK_MAX_LRO_RX_LENGTH(4096 * 3) > PAGE_SIZE.
> netdev_alloc_frag is for alloction of page fragment only.
> Reference to other drivers and Documentation/vm/page_frags.rst
>
> Branch to use alloc_pages when ring->frag_size > PAGE_SIZE.
>
> Signed-off-by: Chen Lin <chen45464546@....com>
> ---
>  drivers/net/ethernet/mediatek/mtk_eth_soc.c |   22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> index b3b3c07..772d903 100644
> --- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> +++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
> @@ -1467,7 +1467,16 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
>                         goto release_desc;
>
>                 /* alloc new buffer */
> -               new_data = napi_alloc_frag(ring->frag_size);
> +               if (ring->frag_size <= PAGE_SIZE) {
> +                       new_data = napi_alloc_frag(ring->frag_size);
> +               } else {
> +                       struct page *page;
> +                       unsigned int order = get_order(ring->frag_size);
> +
> +                       page = alloc_pages(GFP_ATOMIC | __GFP_COMP |
> +                                           __GFP_NOWARN, order);
> +                       new_data = page ? page_address(page) : NULL;
> +               }
>                 if (unlikely(!new_data)) {
>                         netdev->stats.rx_dropped++;
>                         goto release_desc;
> @@ -1914,7 +1923,16 @@ static int mtk_rx_alloc(struct mtk_eth *eth, int ring_no, int rx_flag)
>                 return -ENOMEM;
>
>         for (i = 0; i < rx_dma_size; i++) {
> -               ring->data[i] = netdev_alloc_frag(ring->frag_size);
> +               if (ring->frag_size <= PAGE_SIZE) {
> +                       ring->data[i] = netdev_alloc_frag(ring->frag_size);
> +               } else {
> +                       struct page *page;
> +                       unsigned int order = get_order(ring->frag_size);
> +
> +                       page = alloc_pages(GFP_KERNEL | __GFP_COMP |
> +                                           __GFP_NOWARN, order);
> +                       ring->data[i] = page ? page_address(page) : NULL;
> +               }
>                 if (!ring->data[i])
>                         return -ENOMEM;
>         }

Actually I looked closer at this driver. Is it able to receive frames
larger than 2K? If not there isn't any point in this change.

Based on commit 4fd59792097a ("net: ethernet: mediatek: support
setting MTU") it looks like it doesn't, so odds are this patch is not
necessary.