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From: Alexander Duyck <alexander.h.duyck@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>,
	linux-mm@kvack.org, akpm@linux-foundation.org,
	linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org
Cc: pavel.tatashin@microsoft.com, mhocko@suse.com,
	jglisse@redhat.com, rppt@linux.vnet.ibm.com, mingo@kernel.org,
	kirill.shutemov@linux.intel.com
Subject: Re: [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling page init poisoning
Date: Tue, 25 Sep 2018 15:27:59 -0700	[thread overview]
Message-ID: <61358149-b233-6194-adcf-2c16b9112fd7@linux.intel.com> (raw)
In-Reply-To: <75dde720-c997-51a4-d2e2-8b08eb201550@intel.com>



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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  reply	other threads:[~2018-09-25 22:28 UTC|newest]

Thread overview: 77+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-25 20:18 [PATCH v5 0/4] Address issues slowing persistent memory initialization Alexander Duyck
2018-09-25 20:19 ` [PATCH v5 1/4] mm: Remove now defunct NO_BOOTMEM from depends list for deferred init Alexander Duyck
2018-09-25 21:05   ` Mike Rapoport
2018-09-25 20:20 ` [PATCH v5 2/4] mm: Provide kernel parameter to allow disabling page init poisoning Alexander Duyck
2018-09-25 20:26   ` Dave Hansen
2018-09-25 20:38     ` Alexander Duyck
2018-09-25 22:14       ` Dave Hansen
2018-09-25 22:27         ` Alexander Duyck [this message]
2018-09-26  7:38   ` Michal Hocko
2018-09-26 15:24     ` Alexander Duyck
2018-09-26 15:39       ` Michal Hocko
2018-09-26 15:41       ` Dave Hansen
2018-09-26 16:18         ` Alexander Duyck
2018-09-26 15:36     ` Dave Hansen
2018-09-26 22:36       ` Andrew Morton
2018-09-25 20:20 ` [PATCH v5 3/4] mm: Create non-atomic version of SetPageReserved for init use Alexander Duyck
2018-09-25 20:21 ` [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Alexander Duyck
2018-09-26  7:55   ` Michal Hocko
2018-09-26 18:25     ` Alexander Duyck
2018-09-26 18:52       ` Dan Williams
2018-09-27 11:20         ` Michal Hocko
2018-09-27 11:09       ` Michal Hocko
2018-09-27 12:25         ` Oscar Salvador
2018-09-27 13:13           ` Michal Hocko
2018-09-27 14:50             ` Oscar Salvador
2018-09-27 15:41               ` David Hildenbrand
2018-09-28  8:12             ` Oscar Salvador
2018-09-28  8:44               ` Oscar Salvador
2018-09-28 15:50                 ` Dan Williams
2018-09-27 12:32       ` Oscar Salvador
2018-10-08 21:01   ` Dan Williams
2018-10-08 21:38     ` Alexander Duyck
2018-10-08 22:00       ` Dan Williams
2018-10-08 22:07         ` Alexander Duyck
2018-10-08 22:36         ` Alexander Duyck
2018-10-08 22:59           ` Dan Williams
2018-10-08 23:34     ` [mm PATCH] memremap: Fix reference count for pgmap in devm_memremap_pages Alexander Duyck
2018-10-09  0:20       ` Dan Williams
2018-10-09 17:00   ` [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap Yi Zhang
2018-10-09 18:04     ` Dan Williams
2018-10-09 20:26       ` Alexander Duyck
2018-10-09 21:19         ` Dan Williams
2018-10-10 12:52           ` Yi Zhang
2018-10-10 15:27             ` Alexander Duyck
2018-10-11  8:17               ` Yi Zhang
2018-10-10  9:58         ` Michal Hocko
2018-10-10 16:39           ` Alexander Duyck
2018-10-10 17:24             ` Michal Hocko
2018-10-10 17:39               ` Alexander Duyck
2018-10-10 17:53                 ` Michal Hocko
2018-10-10 18:13                   ` Alexander Duyck
2018-10-10 18:52                 ` Michal Hocko
2018-10-11  8:55                   ` Michal Hocko
2018-10-11 17:38                     ` Alexander Duyck
2018-10-11 18:22                       ` Dan Williams
2018-10-17  7:52                       ` Michal Hocko
2018-10-17 15:02                         ` Alexander Duyck
2018-10-29 14:12                           ` Michal Hocko
2018-10-29 15:59                             ` Alexander Duyck
2018-10-29 16:35                               ` Michal Hocko
2018-10-29 17:01                                 ` Alexander Duyck
2018-10-29 17:24                                   ` Michal Hocko
2018-10-29 17:34                                     ` Dan Williams
2018-10-29 17:45                                       ` Michal Hocko
2018-10-29 17:42                                     ` Alexander Duyck
2018-10-29 18:18                                       ` Michal Hocko
2018-10-29 19:59                                         ` Alexander Duyck
2018-10-30  6:29                                           ` Michal Hocko
2018-10-30  6:55                                             ` Dan Williams
2018-10-30  8:17                                               ` Michal Hocko
2018-10-30 15:57                                                 ` Dan Williams
2018-10-30  8:05                                           ` Oscar Salvador
2018-10-29 15:49                           ` Dan Williams
2018-10-29 15:56                             ` Michal Hocko
2018-10-10 18:18               ` Dan Williams
2018-10-11  8:39                 ` Yi Zhang
2018-10-11 15:38                   ` Alexander Duyck

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