linux-kernel - LPC Traffic Shaping w/ BPF Talk

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Message-ID: <20181120221659.GA61322@dennisz-mbp.dhcp.thefacebook.com>
Date:   Tue, 20 Nov 2018 17:16:59 -0500
From:   Dennis Zhou <dennis@...nel.org>
To:     Eddie Hao <eddieh@...gle.com>, Vlad Dumitrescu <vladum@...gle.com>,
        Willem de Bruijn <willemb@...gle.com>
Cc:     Alexei Starovoitov <ast@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: LPC Traffic Shaping w/ BPF Talk - percpu followup

Hi Eddie, Vlad, and Willem,

A few people mentioned to me that you guys were experiencing issues with
the percpu memory allocator. I saw the talk slides mention the
following two bullets:

1) allocation pattern makes the per cpu allocator reach a highly
   fragmented state
2) sometimes takes a long time (up to 12s) to create the PERCPU_HASH
   maps at startup

Could you guys elaborate a little more about the above? Some things
that would help: kernel version, cpu info, and a reproducer if possible?

Also, I did some work last summer to make percpu allocation more
efficient, which went into the 4.14 kernel. Just to be sure, is that a
part of the kernel you guys are running?

Thanks,
Dennis