Re: [PATCH v3 1/6] cgroup: Allow registration and lookup of cgroup private data

From: Tejun Heo <tj@kernel.org>
To: Alexei Starovoitov <ast@fb.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
	intel-gfx@lists.freedesktop.org,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	cgroups@vger.kernel.org, kernel-team@fb.com,
	Roman Gushchin <guro@fb.com>
Subject: Re: [PATCH v3 1/6] cgroup: Allow registration and lookup of cgroup private data
Date: Tue, 13 Mar 2018 15:13:14 -0700	[thread overview]
Message-ID: <20180313221314.GR2943022@devbig577.frc2.facebook.com> (raw)
In-Reply-To: <36e459e1-dd65-8153-7ac4-1629550cce92@fb.com>

Hello,

On Tue, Mar 13, 2018 at 02:47:45PM -0700, Alexei Starovoitov wrote:
> it has to be zero lookups. If idr lookup is involved, it's cleaner
> to add idr as new bpf map type and use cgroup ino as an id.

Oh, idr (or rather ida) is just to allocate the key, once the key is
there it pretty much should boil down to sth like

	rcu_read_lock();
	table = rcu_deref(cgrp->table);
	if (key < table->len)
		ret = table[key];
	else
		ret = NULL;
	rcu_read_unlock();

Depending on the requirements, we can get rid of the table->len check
by making key alloc path more expensive (ie. give out key only after
table extension is fully done and propagated).

Thanks.

-- 
tejun
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