Re: [PATCH V12] mm/debug: Add tests validating architecture page table helpers

On Mon, 2020-02-03 at 16:14 +0100, Christophe Leroy wrote:

Le 02/02/2020 à 12:26, Qian Cai a écrit :

quoted

quoted

On Jan 30, 2020, at 9:13 AM, Christophe Leroy [off-list ref] 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