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

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