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 11:59:56 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Chen Lin <chen45464546@....com>, Felix Fietkau <nbd@....name>,
        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, 3 Jun 2022 10:25:16 -0700 Eric Dumazet wrote:
> >                         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.

Do cases where netdev_alloc_frag() is not run from a process context
from to your mind? My feeling is that the prevailing pattern is what
this driver does, which is netdev_alloc_frag() at startup / open and
napi_alloc_frag() from the datapath. So maybe we can even spare the
detail in the API and have napi_alloc_frag() assume GFP_KERNEL by
default?