Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH net v2 0/2] Revert the 'socket_alloc' life cycle change
To:     SeongJae Park <sjpark@amazon.com>,
        Eric Dumazet <edumazet@google.com>
Cc:     David Miller <davem@davemloft.net>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jakub Kicinski <kuba@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        sj38.park@gmail.com, netdev <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        SeongJae Park <sjpark@amazon.de>, snu@amazon.com,
        amit@kernel.org, stable@vger.kernel.org
References: <20200505150717.5688-1-sjpark@amazon.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <a8510327-d4f0-1207-1342-d688e9d5b8c3@gmail.com>
Date:   Tue, 5 May 2020 08:20:50 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.6.0
MIME-Version: 1.0
In-Reply-To: <20200505150717.5688-1-sjpark@amazon.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 5/5/20 8:07 AM, SeongJae Park wrote:
> On Tue, 5 May 2020 07:53:39 -0700 Eric Dumazet <edumazet@google.com> wrote:
> 

>> Why do we have 10,000,000 objects around ? Could this be because of
>> some RCU problem ?
> 
> Mainly because of a long RCU grace period, as you guess.  I have no idea how
> the grace period became so long in this case.
> 
> As my test machine was a virtual machine instance, I guess RCU readers
> preemption[1] like problem might affected this.
> 
> [1] https://www.usenix.org/system/files/conference/atc17/atc17-prasad.pdf
> 
>>
>> Once Al patches reverted, do you have 10,000,000 sock_alloc around ?
> 
> Yes, both the old kernel that prior to Al's patches and the recent kernel
> reverting the Al's patches didn't reproduce the problem.
>

I repeat my question : Do you have 10,000,000 (smaller) objects kept in slab caches ?

TCP sockets use the (very complex, error prone) SLAB_TYPESAFE_BY_RCU, but not the struct socket_wq
object that was allocated in sock_alloc_inode() before Al patches.

These objects should be visible in kmalloc-64 kmem cache.