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Subject: Re: Problem in pfmemalloc skb handling in net/core/dev.c
To:     Xie He <xie.he.0141@gmail.com>,
        Eric Dumazet <eric.dumazet@gmail.com>
Cc:     Mel Gorman <mgorman@techsingularity.net>,
        Mel Gorman <mgorman@suse.de>, jslaby@suse.cz,
        Neil Brown <neilb@suse.de>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Mike Christie <michaelc@cs.wisc.edu>,
        Eric B Munson <emunson@mgebm.net>,
        Sebastian Andrzej Siewior <sebastian@breakpoint.cc>,
        Christoph Lameter <cl@linux.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Linux Kernel Network Developers <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <3c79924f-3603-b259-935a-2e913dc3afcd@gmail.com>
Date:   Fri, 9 Apr 2021 13:50:15 +0200
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On 4/9/21 12:14 PM, Xie He wrote:
> On Fri, Apr 9, 2021 at 3:04 AM Eric Dumazet <eric.dumazet@gmail.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.