netdev - Re: [PATCH] net: ipv4: Cache pmtu for all packet paths if multipath enabled

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Message-ID: <ad29493c-9e48-4a94-b327-e47af3a9d137@kernel.org>
Date: Wed, 6 Nov 2024 11:57:25 -0700
From: David Ahern <dsahern@...nel.org>
To: Vladimir Vdovin <deliran@...dict.gg>, Ido Schimmel <idosch@...sch.org>
Cc: netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH] net: ipv4: Cache pmtu for all packet paths if multipath
 enabled

On 11/6/24 10:20 AM, Vladimir Vdovin wrote:
> On Tue Nov 5, 2024 at 6:52 AM MSK, David Ahern wrote:
>> On 11/2/24 10:20 AM, Vladimir Vdovin wrote:
>>>>
>>>> Doesn't IPv6 suffer from a similar problem?
>>
>> I believe the answer is yes, but do not have time to find a reproducer
>> right now.
>>
>>>
>>> I am not very familiar with ipv6,
>>> but I tried to reproduce same problem with my tests with same topology.
>>>
>>> ip netns exec ns_a-AHtoRb ip -6 r g fc00:1001::2:2 sport 30003 dport 443
>>> fc00:1001::2:2 via fc00:2::2 dev veth_A-R2 src fc00:1000::1:1 metric 1024 expires 495sec mtu 1500 pref medium
>>>
>>> ip netns exec ns_a-AHtoRb ip -6 r g fc00:1001::2:2 sport 30013 dport 443
>>> fc00:1001::2:2 via fc00:1::2 dev veth_A-R1 src fc00:1000::1:1 metric 1024 expires 484sec mtu 1500 pref medium

you should dump the cache to see the full exception list.

>>>
>>> It seems that there are no problems with ipv6. We have nhce entries for both paths.
>>
>> Does rt6_cache_allowed_for_pmtu return true or false for this test?
> It returns true.
> 
> 

Looking at the code, it is creating a single exception - not one per
path. I am fine with deferring the ipv6 patch until someone with time
and interest can work on it.