Re: [PATCH] kretprobe scalability improvement

[Masami Hiramatsu]

On Sun, 4 Jul 2021 10:16:47 +0100
Christoph Hellwig <hch@xxxxxxxxxxxxx> 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@xxxxxxxxxx>