linux-kernel - Re: What should we be doing to stress-test kfree

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Date:   Wed, 1 Apr 2020 23:16:07 +0200
From:   Uladzislau Rezki <urezki@...il.com>
To:     Joel Fernandes <joel@...lfernandes.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>, urezki@...il.com,
        linux-kernel@...r.kernel.org, rcu@...r.kernel.org
Subject: Re: What should we be doing to stress-test kfree_rcu()?

On Wed, Apr 01, 2020 at 04:50:12PM -0400, Joel Fernandes wrote:
> On Wed, Apr 01, 2020 at 11:44:15AM -0700, Paul E. McKenney wrote:
> > Hello!
> > 
> > What should we be doing to stress-test kfree_rcu(), including its ability
> > to cope with OOM conditions?  Yes, rcuperf runs are nice, but they are not
> > currently doing much more than testing base functionality, performance,
> > and scalability.
> 
> I already stress kfree_rcu() with rcuperf right now to a point of OOM and
> make sure it does not OOM. The way I do this is set my VM to low memory (like
> 512MB) and then flood kfree_rcu()s. After the shrinker changes, I don't see
> OOM with my current rcuperf settings.
> 
> Not saying that my testing is sufficient, just saying this is what I do. It
> would be good to get a real workload to trigger lot of kfree_rcu() activity
> as well especially on low memory systems. Any ideas on that?
> 
> One idea could be to trigger memory pressure from unrelated allocations (such
> as userspace memory hogs), and see how it perform with memory-pressure. For
> one, the shrinker should trigger in such situations to force the queue into
> waiting for a GP in such situations instead of batching too much.
> 
> We are also missing vmalloc() tests. I remember Vlad had some clever vmalloc
> tests around for his great vmalloc rewrites :). Vlad, any thoughts on getting
> to stress kvfree_rcu()?
> 
Actually i updated(localy for my tests) the lib/test_vmalloc.c module with extra
test cases to stress kvfree_rcu() stuff. I think i should add them :)

--
Vlad Rezki