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

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Date:	Wed, 27 Jan 2016 09:19:18 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Christian Borntraeger <borntraeger@...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 Tue, Jan 26, 2016 at 03:29:38PM -0800, David Rientjes wrote:
> On Tue, 26 Jan 2016, Heiko Carstens wrote:
> 
> > On Tue, Jan 26, 2016 at 10:18:25AM +0100, Christian Borntraeger wrote:
> > > We can use debug_pagealloc_enabled() to check if we can map
> > > the identity mapping with 1MB/2GB pages as well as to print
> > > the current setting in dump_stack.
> > > 
> > > Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
> > > ---
> > >  arch/s390/kernel/dumpstack.c |  4 +++-
> > >  arch/s390/mm/vmem.c          | 10 ++++------
> > >  2 files changed, 7 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/arch/s390/kernel/dumpstack.c b/arch/s390/kernel/dumpstack.c
> > > index dc8e204..a1c0530 100644
> > > --- a/arch/s390/kernel/dumpstack.c
> > > +++ b/arch/s390/kernel/dumpstack.c
> > > @@ -11,6 +11,7 @@
> > >  #include <linux/export.h>
> > >  #include <linux/kdebug.h>
> > >  #include <linux/ptrace.h>
> > > +#include <linux/mm.h>
> > >  #include <linux/module.h>
> > >  #include <linux/sched.h>
> > >  #include <asm/processor.h>
> > > @@ -186,7 +187,8 @@ void die(struct pt_regs *regs, const char *str)
> > >  	printk("SMP ");
> > >  #endif
> > >  #ifdef CONFIG_DEBUG_PAGEALLOC
> > > -	printk("DEBUG_PAGEALLOC");
> > > +	printk("DEBUG_PAGEALLOC(%s)",
> > > +		debug_pagealloc_enabled() ? "enabled" : "disabled");
> > >  #endif
> > 
> > I'd prefer if you change this to
> > 
> > 	if (debug_pagealloc_enabled())
> > 		printk("DEBUG_PAGEALLOC");
> > 
> > That way we can get rid of yet another ifdef. Having
> > "DEBUG_PAGEALLOC(disabled)" doesn't seem to be very helpful.
> > 
> 
> 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.

Thanks.