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Date:   Mon, 07 Sep 2020 19:18:48 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Dust Li <dust.li@...ux.alibaba.com>,
        "David S . Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH] net/sock: don't drop udp packets if udp_mem[2] not
 reached

Hi,

On Mon, 2020-09-07 at 22:44 +0800, Dust Li wrote:
> We encoutered udp packets drop under a pretty low pressure
> with net.ipv4.udp_mem[0] set to a small value (4096).
> 
> After some tracing and debugging, we found that for udp
> protocol, __sk_mem_raise_allocated() will possiblly drop
> packets if:
>   udp_mem[0] < udp_prot.memory_allocated < udp_mem[2]
> 
> That's because __sk_mem_raise_allocated() didn't handle
> the above condition for protocols like udp who doesn't
> have sk_has_memory_pressure()
> 
> We can reproduce this with the following condition
> 1. udp_mem[0] is relateive small,
> 2. net.core.rmem_default/max > udp_mem[0] * 4K

This looks like something that could/should be addressed at
configuration level ?!?

udp_mem[0] should accomodate confortably at least a socket.

Cheers,

Paolo

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