Re: [PATCH v2] hugetlb: allow to free gigantic pages regardless of the configuration

[Alexandre Ghiti]

On 02/14/2019 10:52 AM, Vlastimil Babka wrote:
> On 2/13/19 8:30 PM, Dave Hansen wrote:
> > > -#if (defined(CONFIG_MEMORY_ISOLATION) && defined(CONFIG_COMPACTION)) || defined(CONFIG_CMA)
> > > +#ifdef CONFIG_COMPACTION_CORE
> > >   static __init int gigantic_pages_init(void)
> > >   {
> > >   	/* With compaction or CMA we can allocate gigantic pages at runtime */
> > > diff --git a/fs/Kconfig b/fs/Kconfig
> > > index ac474a61be37..8fecd3ea5563 100644
> > > --- a/fs/Kconfig
> > > +++ b/fs/Kconfig
> > > @@ -207,8 +207,9 @@ config HUGETLB_PAGE
> > >   config MEMFD_CREATE
> > >   	def_bool TMPFS || HUGETLBFS
> > >   
> > > -config ARCH_HAS_GIGANTIC_PAGE
> > > +config COMPACTION_CORE
> > >   	bool
> > > +	default y if (MEMORY_ISOLATION && MIGRATION) || CMA
> > This takes a hard dependency (#if) and turns it into a Kconfig *default*
> > that can be overridden.  That seems like trouble.
> >
> > Shouldn't it be:
> >
> > config COMPACTION_CORE
> > 	def_bool y
> > 	depends on (MEMORY_ISOLATION && MIGRATION) || CMA
> Agreed. Also I noticed that it now depends on MIGRATION instead of
> COMPACTION. That intention is correct IMHO, but will fail to
> compile/link when both COMPACTION and CMA are disabled, and would need
> more changes in mm/internal.h and mm/compaction.c (possibly just
> replacing CMA in all "if defined CONFIG_COMPACTION || defined
> CONFIG_CMA" instances with COMPACTION_CORE, but there might be more
> problems, wanna try? :)

Let's be honest, that's a "typo" :) Migration is logical to me but
that's because I don't know much about compaction. Thanks for
noticing it.
I'll take a look at what you propose to do too.

> Also, I realized that COMPACTION_CORE is a wrong name, sorry about that.
> What the config really provides is alloc_contig_range(), so it should be
> named either CONFIG_CMA_CORE (as it provides contiguous memory
> allocation, but not the related reservation and accounting), or
> something like CONFIG_CONTIG_ALLOC. I would also move it from fs/Kconfig
> to mm/Kconfig.

No problem, I was not inspired either. I'll send a v3 with the renaming
you propose.

> Thanks!

Thank you.

Alex