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

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Date:   Thu, 14 Feb 2019 11:59:18 +0100
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Vlastimil Babka <vbabka@...e.cz>,
        Dave Hansen <dave.hansen@...el.com>,
        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

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