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

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Message-ID: <56A8C175.9030702@de.ibm.com>
Date:	Wed, 27 Jan 2016 14:09:09 +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 02:03 PM, Vlastimil Babka wrote:
> On 01/27/2016 01:47 PM, Christian Borntraeger wrote:
>> On 01/27/2016 01:41 PM, Vlastimil Babka wrote:
>>> On 01/27/2016 01:59 AM, Joonsoo Kim wrote:
>>>
>>> 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?
> 
> Well, mostly kernel_map_pages() which is used in page allocation hotpaths.

Right. So indeed, static_key would be a good thing, but certainly an addon patch.