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

From	Joonsoo Kim <iamjoonsoo.kim@lge.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting
Date	2016-01-28 05:40 +0100
Message-ID	<qVMxb-6iO-3@gated-at.bofh.it> (permalink)
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On Wed, Jan 27, 2016 at 02:03:36PM +0100, 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.

We cannot just convert it because setup_arch() is called before
jump_label_init(). We can do it by introducing _early variant but
I'm not sure it's worth doing. I think that just make it unlikely
works well. Recently, I tested a micro benchmark on slab alloc/free
on CONFIG_SLUB with applying static branch for debug option which
currently is using unlikely branch and can't find any noticeble
performance difference.

Thanks.

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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
                Re: [PATCH/RFC 3/3] s390: query dynamic DEBUG_PAGEALLOC setting Joonsoo Kim <iamjoonsoo.kim@lge.com> - 2016-01-28 05:40 +0100

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