Message-ID: <f6a5d04b-cb89-7939-33f0-3cce84c67782@nbd.name>
Date:   Fri, 27 Jan 2023 08:21:38 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0)
 Gecko/20100101 Thunderbird/102.6.1
Subject: Re: [net PATCH] skb: Do mix page pool and page referenced frags in
 GRO
Content-Language: en-US
To:     Jakub Kicinski <kuba@kernel.org>,
        Alexander Duyck <alexander.duyck@gmail.com>
Cc:     davem@davemloft.net, edumazet@google.com, hawk@kernel.org,
        ilias.apalodimas@linaro.org, linux-kernel@vger.kernel.org,
        linyunsheng@huawei.com, lorenzo@kernel.org, netdev@vger.kernel.org,
        pabeni@redhat.com
References: <04e27096-9ace-07eb-aa51-1663714a586d@nbd.name>
 <167475990764.1934330.11960904198087757911.stgit@localhost.localdomain>
 <20230126151317.73d67045@kernel.org>
From:   Felix Fietkau <nbd@nbd.name>
In-Reply-To: <20230126151317.73d67045@kernel.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 27.01.23 00:13, Jakub Kicinski wrote:
> On Thu, 26 Jan 2023 11:06:59 -0800 Alexander Duyck wrote:
>> From: Alexander Duyck <alexanderduyck@fb.com>
>> 
>> GSO should not merge page pool recycled frames with standard reference
>> counted frames. Traditionally this didn't occur, at least not often.
>> However as we start looking at adding support for wireless adapters there
>> becomes the potential to mix the two due to A-MSDU repartitioning frames in
>> the receive path. There are possibly other places where this may have
>> occurred however I suspect they must be few and far between as we have not
>> seen this issue until now.
>> 
>> Fixes: 53e0961da1c7 ("page_pool: add frag page recycling support in page pool")
>> Reported-by: Felix Fietkau <nbd@nbd.name>
>> Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
> 
> Exciting investigation!
> Felix, out of curiosity - the impact of loosing GRO on performance is
> not significant enough to care?  We could possibly try to switch to
> using the frag list if we can't merge into frags safely.
Since this only affects combining page_pool and non-page_pool packets, 
the performance loss should be neglegible.

- Felix