linux-kernel - Re: [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling page init poisoning

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Message-ID: <8faf3acc-e47e-8ef9-a1a0-c0d6ebfafa1e@linux.intel.com>
Date:   Tue, 25 Sep 2018 13:38:43 -0700
From:   Alexander Duyck <alexander.h.duyck@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-nvdimm@...ts.01.org
Cc:     pavel.tatashin@...rosoft.com, mhocko@...e.com,
        dave.jiang@...el.com, jglisse@...hat.com, rppt@...ux.vnet.ibm.com,
        dan.j.williams@...el.com, logang@...tatee.com, mingo@...nel.org,
        kirill.shutemov@...ux.intel.com
Subject: Re: [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling
 page init poisoning

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".