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    SubjectRe: [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling page init poisoning
    On Wed 26-09-18 08:24:56, Alexander Duyck wrote:
    > On 9/26/2018 12:38 AM, Michal Hocko wrote:
    > > On Tue 25-09-18 13:20:12, Alexander Duyck wrote:
    > > [...]
    > > > + vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
    > > > + May slow down system boot speed, especially when
    > > > + enabled on systems with a large amount of memory.
    > > > + All options are enabled by default, and this
    > > > + interface is meant to allow for selectively
    > > > + enabling or disabling specific virtual memory
    > > > + debugging features.
    > > > +
    > > > + Available options are:
    > > > + P Enable page structure init time poisoning
    > > > + - Disable all of the above options
    > >
    > > I agree with Dave that this is confusing as hell. So what does vm_debug
    > > (without any options means). I assume it's NOP and all debugging is
    > > enabled and that is the default. What if I want to disable _only_ the
    > > page struct poisoning. The weird lookcing `-' will disable all other
    > > options that we might gather in the future.
    >
    > With no options it works just like slub_debug and enables all available
    > options. So in our case it is a NOP since we wanted the debugging enabled by
    > default.

    But isn't slub_debug more about _adding_ debugging features? While you
    want to effectively disbale some debugging features here? So if you want
    to follow that pattern then it would be something like
    vm_debug_disable=page_poisoning,$OTHER_FUTURE_DEBUG_OPTIONS

    why would you want to enable something when CONFIG_DEBUG_VM=y just
    enables everything?

    > > Why cannot you simply go with [no]vm_page_poison[=on/off]?
    >
    > That is what I had to begin with, but Dave Hansen and Dan Williams suggested
    > that I go with a slub_debug style interface so we could extend it in the
    > future.

    Please let's not over-engineer this. If you really need an umbrella
    parameter then make a list of things to disable.
    --
    Michal Hocko
    SUSE Labs

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