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Date:   Mon, 5 Jul 2021 08:59:01 +0900
From:   Masami Hiramatsu <mhiramat@kernel.org>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     "wuqiang.matt" <wuqiang.matt@bytedance.com>,
        naveen.n.rao@linux.ibm.com, anil.s.keshavamurthy@intel.com,
        davem@davemloft.net, mhiramat@kernel.org, mingo@kernel.org,
        peterz@infradead.org, linux-kernel@vger.kernel.org, mattwu@163.com
Subject: Re: [PATCH] kretprobe scalability improvement
Message-Id: <20210705085901.20f97a48c37fdc533d554dc6@kernel.org>
In-Reply-To: <YOF8fyJIzJmZUhoC@infradead.org>
References: <20210703102818.20766-1-wuqiang.matt@bytedance.com>
        <YOF8fyJIzJmZUhoC@infradead.org>
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On Sun, 4 Jul 2021 10:16:47 +0100
Christoph Hellwig <hch@infradead.org> wrote:

> Would it make sense to just reuse kernel/bpf/percpu_freelist.c for
> kretprobes?

Hmm, I don't think so.
It seems that what Wuqiang proposed is more efficient than the 
percpu_freelist, and it will be less efficient from the viewpoint
of memory usage because kretprobe freelist manages instance pool
among all CPUs (which can be unbalanced, sometimes 95% used by one
core, sometimes used evenly).

Actually, the best solution is to have per-task fixed-size instance
pool which is shared by all kretprobes (e.g. 4kb/task), because
the instance makes a "shadow stack" for each task. This may consume
more memory but is not increased by adding kretprobes, and should be
scalable.

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>