Re: [PATCH 14/17] mm: Make hibernate handle unmapped pages

From: Pavel Machek <pavel@ucw.cz>
To: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
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Subject: Re: [PATCH 14/17] mm: Make hibernate handle unmapped pages
Date: Fri, 18 Jan 2019 00:41:11 +0100	[thread overview]
Message-ID: <20190117234111.GA27661@amd> (raw)
In-Reply-To: <b224d88d91a5c45c44e176ea06dea558a8939ccf.camel@intel.com>

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Hi!

> > > For architectures with CONFIG_ARCH_HAS_SET_ALIAS, pages can be unmapped
> > > briefly on the directmap, even when CONFIG_DEBUG_PAGEALLOC is not
> > > configured.
> > > So this changes kernel_map_pages and kernel_page_present to be defined when
> > > CONFIG_ARCH_HAS_SET_ALIAS is defined as well. It also changes places
> > > (page_alloc.c) where those functions are assumed to only be implemented when
> > > CONFIG_DEBUG_PAGEALLOC is defined.
> > 
> > Which architectures are that?
> > 
> > Should this be merged to the patch where HAS_SET_ALIAS is introduced? We
> > don't want broken hibernation in between....
> Thanks for taking a look. It was added for x86 for patch 13 in this patchset and
> there was interest expressed for adding for arm64. If you didn't get the whole
> set and want to see let me know and I can send it.

I googled in in the meantime.

Anyway, if something is broken between patch 13 and 14, then they
should be same patch.

> > > -#ifdef CONFIG_DEBUG_PAGEALLOC
> > >  extern bool _debug_pagealloc_enabled;
> > > -extern void __kernel_map_pages(struct page *page, int numpages, int
> > > enable);
> > >  
> > >  static inline bool debug_pagealloc_enabled(void)
> > >  {
> > > -	return _debug_pagealloc_enabled;
> > > +	return IS_ENABLED(CONFIG_DEBUG_PAGEALLOC) && _debug_pagealloc_enabled;
> > >  }
> > 
> > This will break build AFAICT. _debug_pagealloc_enabled variable does
> > not exist in !CONFIG_DEBUG_PAGEALLOC case.
> > 
> > 									Pavel
> After adding in the CONFIG_ARCH_HAS_SET_ALIAS condition to the ifdefs in this
> area it looked a little hard to read to me, so I moved debug_pagealloc_enabled
> and extern bool _debug_pagealloc_enabled outside to make it easier. I think you
> are right, the actual non-extern variable can not be there, but the reference
> here gets optimized out in that case.
> 
> Just double checked and it builds for both CONFIG_DEBUG_PAGEALLOC=n and
> CONFIG_DEBUG_PAGEALLOC=y for me.

Ok.

Thanks,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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