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Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting

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On 01/27/2016 01:59 AM, Joonsoo Kim wrote:
> On Tue, Jan 26, 2016 at 04:36:11PM -0800, David Rientjes wrote:
>> On Wed, 27 Jan 2016, Joonsoo Kim wrote:
>>
>>>> I'd agree if CONFIG_DEBUG_PAGEALLOC only did anything when 
>>>> debug_pagealloc_enabled() is true, but that doesn't seem to be the case.  
>>>> When CONFIG_DEBUG_SLAB is enabled, for instance, CONFIG_DEBUG_PAGEALLOC 
>>>> also enables stackinfo storing and poisoning and it's not guarded by 
>>>> debug_pagealloc_enabled().
>>>>
>>>> It seems like CONFIG_DEBUG_PAGEALLOC enables debugging functionality 
>>>> outside the scope of the debug_pagealloc=on kernel parameter, so 
>>>> DEBUG_PAGEALLOC(disabled) actually does mean something.
>>>
>>> Hello, David.
>>>
>>> I tried to fix CONFIG_DEBUG_SLAB case on 04/16 of following patchset.
>>>
>>> http://thread.gmane.org/gmane.linux.kernel.mm/144527
>>>
>>> I found that there are more sites to fix but not so many.
>>> We can do it.
>>>
>>
>> For the slab case, sure, this can be fixed, but there is other code that 
>> uses CONFIG_DEBUG_PAGEALLOC to suggest debugging is always enabled and is 
>> indifferent to debug_pagealloc_enabled().  I find this in powerpc and 
>> sparc arch code as well as generic vmalloc code.  
> 
> Yes, I also found it.
> 
>>
>> If we can convert existing users that only check for 
>> CONFIG_DEBUG_PAGEALLOC to rather check for debug_pagealloc_enabled() and 
>> agree that it is only enabled for debug_pagealloc=on, then this would seem 
>> fine.  However, I think we should at least consult with those users before 
>> removing an artifact from the kernel log that could be useful in debugging 
>> why a particular BUG() happened.
> 
> Yes, at least, non-architecture dependent code (vmalloc, SLAB, SLUB) should
> be changed first. If Christian doesn't mind, I will try to fix above 3
> things.

Ok. So I will change this as Heiko and Thomas suggested for s390 and x86 and 
resend these 3 patches. Feel free to work on the other areas.

Christian

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[PATCH/RFC 0/3] Optimize CONFIG_DEBUG_PAGEALLOC Christian Borntraeger <borntraeger@de.ibm.com> - 2016-01-26 10:20 +0100
  [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Christian Borntraeger <borntraeger@de.ibm.com> - 2016-01-26 10:20 +0100
    Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Heiko Carstens <heiko.carstens@de.ibm.com> - 2016-01-26 19:20 +0100
      Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Thomas Gleixner <tglx@linutronix.de> - 2016-01-26 21:50 +0100
      Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting David Rientjes <rientjes@google.com> - 2016-01-27 00:30 +0100
        Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-01-27 01:20 +0100
          Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting David Rientjes <rientjes@google.com> - 2016-01-27 01:40 +0100
            Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-01-27 02:00 +0100
              Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Christian Borntraeger <borntraeger@de.ibm.com> - 2016-01-27 09:00 +0100
              Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Vlastimil Babka <vbabka@suse.cz> - 2016-01-27 13:50 +0100
                Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Christian Borntraeger <borntraeger@de.ibm.com> - 2016-01-27 13:50 +0100
                Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Christian Borntraeger <borntraeger@de.ibm.com> - 2016-01-27 14:10 +0100
                Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Vlastimil Babka <vbabka@suse.cz> - 2016-01-27 14:10 +0100

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