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Message-ID: <20150407093145.GA10348@gmail.com>
Date: Tue, 7 Apr 2015 11:31:45 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Sasha Levin <sasha.levin@...cle.com>,
LKML <linux-kernel@...r.kernel.org>,
Rusty Russell <rusty@...tcorp.com.au>,
Dave Jones <davej@...hat.com>, Michal Hocko <mhocko@...e.cz>,
Borislav Petkov <bp@...en8.de>,
the arch/x86 maintainers <x86@...nel.org>
Subject: Re: Hang on large copy_from_user with PREEMPT_NONE
* Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> On Mon, Apr 6, 2015 at 12:08 PM, Sasha Levin <sasha.levin@...cle.com> wrote:
> >
> > Your patch just makes it hang in memset instead:
>
> So it's certainly a big memset (2GB or so: original count in RDX:
> 0x7e777000, and "%rcx << 6" is bytes left, so it has done about 85%
> of it), which is certainly going to be slow, but it shouldn't
> *hang*. [...]
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.
Thanks,
Ingo
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