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Subject: Re: [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling
 page init poisoning
To:     Dave Hansen <dave.hansen@intel.com>, linux-mm@kvack.org,
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From:   Alexander Duyck <alexander.h.duyck@linux.intel.com>
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Date:   Tue, 25 Sep 2018 13:38:43 -0700
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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.

Either I can do this as a single parameter that supports on/off 
semantics, or I can support it as a slub_debug type parameter that does 
flags based on the input options. I would rather not muddy things by 
trying to do both.

> Also, 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".