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

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Message-ID: <d367b5c7-eb05-6d0b-f9bf-5b3fc3f392a9@intel.com>
Date:   Wed, 13 Feb 2019 11:30:11 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Alexandre Ghiti <alex@...ti.fr>, Vlastimil Babka <vbabka@...e.cz>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2] hugetlb: allow to free gigantic pages regardless of
 the configuration

> -#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

?