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Date: Mon, 2 Jul 2018 12:21:12 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v4 00/17] khwasan: kernel hardware assisted address
 sanitizer
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To: Evgenii Stepanov <eugenis@google.com>
Cc: Andrey Konovalov <andreyknvl@google.com>, Andrey Ryabinin <aryabinin@virtuozzo.com>, Alexander Potapenko <glider@google.com>, Dmitry Vyukov <dvyukov@google.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, Christoph Lameter <cl@linux.com>, Mark Rutland <mark.rutland@arm.com>, Nick Desaulniers <ndesaulniers@google.com>, Marc Zyngier <marc.zyngier@arm.com>, Dave Martin <dave.martin@arm.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, "Eric W . Biederman" <ebiederm@xmission.com>, Ingo Molnar <mingo@kernel.org>, Paul Lawrence <paullawrence@google.com>, Geert Uytterhoeven <geert@linux-m68k.org>, Arnd Bergmann <arnd@arndb.de>, "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Kate Stewart <kstewart@linuxfoundation.org>, Mike Rapoport <rppt@linux.vnet.ibm.com>, kasan-dev <kasan-dev@googlegroups.com>, linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>, Linux ARM <linux-arm-kernel@lists.infradead.org>, linux-sparse@vger.kernel.org, Linux Memory Management List <linux-mm@kvack.org>, Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>, Kostya Serebryany <kcc@google.com>, Lee Smith <Lee.Smith@arm.com>, Ramana Radhakrishnan <Ramana.Radhakrishnan@arm.com>, Jacob Bramley <Jacob.Bramley@arm.com>, Ruben Ayrapetyan <Ruben.Ayrapetyan@arm.com>, Jann Horn <jannh@google.com>, Mark Brand <markbrand@google.com>, Chintan Pandya <cpandya@codeaurora.org>

On Mon, 2 Jul 2018 12:16:42 -0700 Evgenii Stepanov <eugenis@google.com> wrote:

> On Fri, Jun 29, 2018 at 7:41 PM, Andrew Morton
> <akpm@linux-foundation.org> wrote:
> > On Fri, 29 Jun 2018 14:45:08 +0200 Andrey Konovalov <andreyknvl@google.com> wrote:
> >
> >> >> What kind of memory consumption testing would you like to see?
> >> >
> >> > Well, 100kb or so is a teeny amount on virtually any machine.  I'm
> >> > assuming the savings are (much) more significant once the machine gets
> >> > loaded up and doing work?
> >>
> >> So with clean kernel after boot we get 40 kb memory usage. With KASAN
> >> it is ~120 kb, which is 200% overhead. With KHWASAN it's 50 kb, which
> >> is 25% overhead. This should approximately scale to any amounts of
> >> used slab memory. For example with 100 mb memory usage we would get
> >> +200 mb for KASAN and +25 mb with KHWASAN. (And KASAN also requires
> >> quarantine for better use-after-free detection). I can explicitly
> >> mention the overhead in %s in the changelog.
> >>
> >> If you think it makes sense, I can also make separate measurements
> >> with some workload. What kind of workload should I use?
> >
> > Whatever workload people were running when they encountered problems
> > with KASAN memory consumption ;)
> >
> > I dunno, something simple.  `find / > /dev/null'?
> >
>
> Looking at a live Android device under load, slab (according to
> /proc/meminfo) + kernel stack take 8-10% available RAM (~350MB).
> Kasan's overhead of 2x - 3x on top of it is not insignificant.
> 

(top-posting repaired.  Please don't)

For a debugging, not-for-production-use feature, that overhead sounds
quite acceptable to me.  What problems is it known to cause?