Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers
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- To: Christophe Leroy <christophe.leroy@xxxxxx>
- Subject: Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers
- From: Qian Cai <cai@xxxxxx>
- Date: Mon, 03 Feb 2020 10:48:14 -0500
- Cc: Anshuman Khandual <Anshuman.Khandual@xxxxxxx>, linux-mm@xxxxxxxxx, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Vlastimil Babka <vbabka@xxxxxxx>, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>, Jason Gunthorpe <jgg@xxxxxxxx>, Dan Williams <dan.j.williams@xxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Michal Hocko <mhocko@xxxxxxxxxx>, Mark Rutland <Mark.Rutland@xxxxxxx>, Mark Brown <broonie@xxxxxxxxxx>, Steven Price <Steven.Price@xxxxxxx>, Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>, Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>, Matthew Wilcox <willy@xxxxxxxxxxxxx>, Sri Krishna chowdary <schowdary@xxxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxx>, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx>, Michael Ellerman <mpe@xxxxxxxxxxxxxx>, Paul Mackerras <paulus@xxxxxxxxx>, Martin Schwidefsky <schwidefsky@xxxxxxxxxx>, Heiko Carstens <heiko.carstens@xxxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, Vineet Gupta <vgupta@xxxxxxxxxxxx>, James Hogan <jhogan@xxxxxxxxxx>, Paul Burton <paul.burton@xxxxxxxx>, Ralf Baechle <ralf@xxxxxxxxxxxxxx>, "Kirill A . Shutemov" <kirill@xxxxxxxxxxxxx>, Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, linux-snps-arc@xxxxxxxxxxxxxxxxxxx, linux-mips@xxxxxxxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linuxppc-dev@xxxxxxxxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, linux-sh@xxxxxxxxxxxxxxx, sparclinux@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, kasan-dev <kasan-dev@xxxxxxxxxxxxxxxx>
- In-reply-to: <8e94a073-4045-89aa-6a3b-24847ad7c858@c-s.fr>
- References: <473d8198-3ac4-af3b-e2ec-c0698a3565d3@c-s.fr> <2C4ADFAE-7BB4-42B7-8F54-F036EA7A4316@lca.pw> <8e94a073-4045-89aa-6a3b-24847ad7c858@c-s.fr>
On Mon, 2020-02-03 at 16:14 +0100, Christophe Leroy wrote:
>
> Le 02/02/2020 à 12:26, Qian Cai a écrit :
> >
> >
> > > On Jan 30, 2020, at 9:13 AM, Christophe Leroy <christophe.leroy@xxxxxx> wrote:
> > >
> > > config DEBUG_VM_PGTABLE
> > > bool "Debug arch page table for semantics compliance" if ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT
> > > depends on MMU
> > > default 'n' if !ARCH_HAS_DEBUG_VM_PGTABLE
> > > default 'y' if DEBUG_VM
> >
> > Does it really necessary to potentially force all bots to run this? Syzbot, kernel test robot etc? Does it ever pay off for all their machine times there?
> >
>
> Machine time ?
>
> On a 32 bits powerpc running at 132 MHz, the tests takes less than 10ms.
> Is it worth taking the risk of not detecting faults by not selecting it
> by default ?
The risk is quite low as Catalin mentioned this thing is not to detect
regressions but rather for arch/mm maintainers.
I do appreciate the efforts to get everyone as possible to run this thing,
so it get more notices once it is broken. However, DEBUG_VM seems like such
a generic Kconfig those days that have even been enabled by default for
Fedora Linux, so I would rather see a more sensitive default been taken
even though the test runtime is fairly quickly on a small machine for now.
>
> [ 5.656916] debug_vm_pgtable: debug_vm_pgtable: Validating
> architecture page table helpers
> [ 5.665661] debug_vm_pgtable: debug_vm_pgtable: Validated
> architecture page table helpers
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