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Date:   Thu, 23 Jun 2022 18:57:30 -0700
From:   Jakub Kicinski <kuba@kernel.org>
To:     Xin Long <lucien.xin@gmail.com>
Cc:     Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
        kernel test robot <oliver.sang@intel.com>,
        Eric Dumazet <edumazet@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        Soheil Hassas Yeganeh <soheil@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        network dev <netdev@vger.kernel.org>,
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        "linux-sctp @ vger . kernel . org" <linux-sctp@vger.kernel.org>,
        lkp@lists.01.org, kbuild test robot <lkp@intel.com>,
        Huang Ying <ying.huang@intel.com>, feng.tang@intel.com,
        zhengjun.xing@linux.intel.com, fengwei.yin@intel.com,
        Ying Xu <yinxu@redhat.com>
Subject: Re: [net] 4890b686f4: netperf.Throughput_Mbps -69.4% regression
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On Thu, 23 Jun 2022 18:50:07 -0400 Xin Long wrote:
> From the perf data, we can see __sk_mem_reduce_allocated() is the one
> using CPU the most more than before, and mem_cgroup APIs are also
> called in this function. It means the mem cgroup must be enabled in
> the test env, which may explain why I couldn't reproduce it.
> 
> The Commit 4890b686f4 ("net: keep sk->sk_forward_alloc as small as
> possible") uses sk_mem_reclaim(checking reclaimable >= PAGE_SIZE) to
> reclaim the memory, which is *more frequent* to call
> __sk_mem_reduce_allocated() than before (checking reclaimable >=
> SK_RECLAIM_THRESHOLD). It might be cheap when
> mem_cgroup_sockets_enabled is false, but I'm not sure if it's still
> cheap when mem_cgroup_sockets_enabled is true.
> 
> I think SCTP netperf could trigger this, as the CPU is the bottleneck
> for SCTP netperf testing, which is more sensitive to the extra
> function calls than TCP.
> 
> Can we re-run this testing without mem cgroup enabled?

FWIW I defer to Eric, thanks a lot for double checking the report 
and digging in!