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SubjectRe: [PATCH 14/17] mm: Make hibernate handle unmapped pages
Date
On Fri, 2019-01-18 at 00:41 +0100, Pavel Machek wrote:
> 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.
Great. It should be ok because the new functions are not used anywhere until
after this patch.

Thanks,

Rick

> > > > -#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
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