Messages in this thread | | | Subject | Re: [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling page init poisoning | From | Alexander Duyck <> | Date | Tue, 25 Sep 2018 15:27:59 -0700 |
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On 9/25/2018 3:14 PM, Dave Hansen wrote: > On 09/25/2018 01:38 PM, Alexander Duyck wrote: >> On 9/25/2018 1:26 PM, Dave Hansen wrote: >>> On 09/25/2018 01:20 PM, 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 >>> >>> Can we have vm_debug=off for turning things off, please? That seems to >>> be pretty standard. >> >> No. The simple reason for that is that you had requested this work like >> the slub_debug. If we are going to do that then each individual letter >> represents a feature. That is why the "-" represents off. We cannot have >> letters represent flags, and letters put together into words. For >> example slub_debug=OFF would turn on sanity checks and turn off >> debugging for caches that would have causes higher minimum slab orders. > > We don't have to have the same letters mean the same things for both > options. We also can live without 'o' and 'f' being valid. We can > *also* just say "don't do 'off'" if you want to enable things.
I'm not saying we do either. I would prefer it if we stuck to similar behavior though. If we are going to do a slub_debug style parameter then we should stick with similar behavior where "-" is used to indicate all features off.
> I'd much rather have vm_debug=off do the right thing than have > per-feature enable/disable. I know I'll *never* remember vm_debug=- and > doing it this way will subject me to innumerable trips to Documentation/ > during my few remaining years. > > Surely you can make vm_debug=off happen. :)
I could, but then it is going to confuse people even more. I really feel that if we want to do a slub_debug style interface we should use the same switch for turning off all the features that they do for slub_debug.
>>> we need to document the defaults. I think the default is "all >>> debug options are enabled", but it would be nice to document that. >> >> In the description I call out "All options are enabled by default, and this interface is meant to allow for selectively enabling or disabling". > > I found "all options are enabled by default" really confusing. Maybe: > > "Control debug features which become available when CONFIG_DEBUG_VM=y. > When this option is not specified, all debug features are enabled. Use > this option enable a specific subset." > > Then, let's actually say what the options do, and what their impact is: > > P Enable 'struct page' poisoning at initialization. > (Slows down boot time). >
From my perspective I just don't see how this changes much since it conveys the same message I had conveyed in my description. Since it looks like Andrew applied the patch feel free to submit your suggestion here as a follow-up patch and I would be willing to review/ack it.
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