Messages in this thread | | | Date | Thu, 17 Jun 2021 22:04:34 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH 2/2] trace/kprobe: Remove limit on kretprobe maxactive |
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Masami Hiramatsu wrote: > On Wed, 16 Jun 2021 11:27:11 +0900 > Masami Hiramatsu <mhiramat@kernel.org> wrote: > >> On Tue, 15 Jun 2021 21:03:51 -0400 >> Steven Rostedt <rostedt@goodmis.org> wrote: >> >> > On Wed, 16 Jun 2021 09:46:22 +0900 >> > Masami Hiramatsu <mhiramat@kernel.org> wrote: >> > >> > > To avoid such trouble, I had set the 4096 limitation for the maxactive >> > > parameter. Of course 4096 may not enough for some use-cases. I'm welcome >> > > to expand it (e.g. 32k, isn't it enough?), but removing the limitation >> > > may cause OOM trouble easily. >> > >> > What if you just made the max as 10 * number of possible cpus, or 4096, >> > which ever is greater? Why would a user need more? >> >> It could be. But actually, that is not correct number because the >> number of instances depends on the number of processes and the possiblity >> of recursive. Thus the huge system which runs more than 64k processes, >> may need more than that. >> >> > I'd still like to get a wrapper around function graph tracing so that >> > kretprobes could use it. I think that would get rid of the requirement >> > of maxactive, because isn't that just used to have a way to know the >> > original return value? >> >> Hmm, yes, on some arch, it can be done. But on other arch we still need >> current implementation for generic solution. >> What I need is not fully wrapped by the function graph, but just share >> the per-task (software) shadow stack. > > BTW, I have 2 ideas to fix this except for wrapper. > > 1. Use func-graph tracer API directly from dynamic event instead of > kretprobes. This will be enabled only if the arch supports fgraph > tracer and enable it. maxactive will be ignored if this is enabled, > and tracefs user may not need except for the return value > (BTW, is that possible to access the stack? In some case, return > value can be passed via stack) > > 2. Move the kretprobe instance pool from kretprobe to struct task. > This pool will allocates one page per task, and shared among all > kretprobes. This pool will be allocated when the 1st kretprobe > is registered. maxactive will be kept for someone who wants to > use per-instance data. But since dynamic event doesn't use it, > it will be removed from tracefs and perf.
Won't this result in _more_ memory usage compared to what we have now?
Thanks, Naveen
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