linux-kernel - Re: Hang on large copy_from_user with PREEMPT

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Message-ID: <20150407143710.GA18777@gmail.com>
Date:	Tue, 7 Apr 2015 16:37:10 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Dave Jones <davej@...hat.com>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: Hang on large copy_from_user with PREEMPT_NONE


* Michal Hocko <mhocko@...e.cz> wrote:

> On Tue 07-04-15 13:05:31, Ingo Molnar wrote:
> > 
> > * Borislav Petkov <bp@...en8.de> wrote:
> > 
> > > On Tue, Apr 07, 2015 at 11:31:45AM +0200, Ingo Molnar wrote:
> > > > Would be nice to see the actual kernel .config, as there's a few
> > > > debug features that can slow things down significantly, such as
> > > > CONFIG_KMEMCHECK=y or in some cases CONFIG_DEBUG_PAGEALLOC=y.
> > > 
> > > He sent it here: https://lkml.kernel.org/r/55229D7E.6080309@oracle.com
> > > 
> > > I'm attaching it again.
> > 
> > Thanks. Nothing particularly expensive stands out to me at a quick 
> > glance:-/
> 
> Sasha uses KASAN very often and it is enabled here as well. I guess 
> this might slow things really down.

Indeed, that kind of instrumentation might explain the overhead ...

Thanks,

	Ingo
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