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 10:25:16 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Chen Lin <chen45464546@....com>
Cc:     Felix Fietkau <nbd@....name>, Jakub Kicinski <kuba@...nel.org>,
        john@...ozen.org, sean.wang@...iatek.com, Mark-MC.Lee@...iatek.com,
        David Miller <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        netdev <netdev@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Duyck <alexander.duyck@...il.com>
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 1:46 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>

...

>                         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);

Note aside, calling netdev_alloc_frag() in a loop like that is adding
GFP_ATOMIC pressure.

mtk_rx_alloc() being in process context, using GFP_KERNEL allocations
would be less aggressive and
have more chances to succeed.

We probably should offer a generic helper. This could be used from
driver/net/tun.c and others.