linux-kernel - Re: Problem in pfmemalloc skb handling in net/core/dev.c

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Date:   Fri, 9 Apr 2021 13:50:15 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Xie He <xie.he.0141@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Mel Gorman <mgorman@...e.de>, jslaby@...e.cz,
        Neil Brown <neilb@...e.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Mike Christie <michaelc@...wisc.edu>,
        Eric B Munson <emunson@...bm.net>,
        Sebastian Andrzej Siewior <sebastian@...akpoint.cc>,
        Christoph Lameter <cl@...ux.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Problem in pfmemalloc skb handling in net/core/dev.c



On 4/9/21 12:14 PM, Xie He wrote:
> On Fri, Apr 9, 2021 at 3:04 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>>
>> Note that pfmemalloc skbs are normally dropped in sk_filter_trim_cap()
>>
>> Simply make sure your protocol use it.
> 
> It seems "sk_filter_trim_cap" needs an "struct sock" argument. Some of
> my protocols act like a middle layer to another protocol and don't
> have any "struct sock".

Then simply copy the needed logic.

> 
> Also, I think this is a problem in net/core/dev.c, there are a lot of
> old protocols that are not aware of pfmemalloc skbs. I don't think
> it's a good idea to fix them one by one.
> 

I think you are mistaken.

There is no problem in net/core/dev.c really, it uses
skb_pfmemalloc_protocol()

pfmemalloc is best effort really.

If a layer store packets in many long living queues, it has to drop pfmemalloc packets,
unless these packets are used for swapping.