linux-kernel - Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG

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Message-ID: <56A8BC6D.9080101@de.ibm.com>
Date:	Wed, 27 Jan 2016 13:47:41 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Vlastimil Babka <vbabka@...e.cz>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	David Rientjes <rientjes@...gle.com>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-arch@...r.kernel.org,
	linux-s390@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting

On 01/27/2016 01:41 PM, Vlastimil Babka wrote:
> On 01/27/2016 01:59 AM, Joonsoo Kim wrote:
>> On Tue, Jan 26, 2016 at 04:36:11PM -0800, David Rientjes wrote:
>>>
>>> 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.
> 
> I think it might be worth also to convert debug_pagealloc_enabled() to be based
> on static key, like I did for page_owner [1]. That should help make it possible
> to have virtually no overhead when compiling kernel with CONFIG_DEBUG_PAGEALLOC
> without enabling it boot-time. I assume it's one of the goals here?

We could do something like that but dump_stack and setup of the initial identity
mapping of the kernel as well as the initial page protection are not hot path
as far as I can tell. Any other places?

> 
> [1] http://www.spinics.net/lists/linux-mm/msg100795.html