linux-kernel - Re: [PATCH v8 4/4] hugetlb: allow to free gigantic pages regardless of the configuration

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Message-ID: <95819dc9-7910-f273-681c-a241fee62dd2@ghiti.fr>
Date:   Wed, 27 Mar 2019 13:54:15 +0100
From:   Alexandre Ghiti <alex@...ti.fr>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        mpe@...erman.id.au, Andrew Morton <akpm@...ux-foundation.org>,
        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>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S . Miller" <davem@...emloft.net>,
        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>,
        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-sh@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v8 4/4] hugetlb: allow to free gigantic pages regardless
 of the configuration

On 03/27/2019 11:05 AM, Aneesh Kumar K.V wrote:
> Alexandre Ghiti <alex@...ti.fr> writes:
>
>> On 03/27/2019 09:55 AM, Aneesh Kumar K.V wrote:
>>> On 3/27/19 2:14 PM, Alexandre Ghiti wrote:
>>>>
>>>> On 03/27/2019 08:01 AM, Aneesh Kumar K.V wrote:
>>>>> On 3/27/19 12:06 PM, Alexandre Ghiti wrote:
> .....
>
>>> This is now
>>> #define __HAVE_ARCH_GIGANTIC_PAGE_RUNTIME_SUPPORTED
>>> static inline bool gigantic_page_runtime_supported(void)
>>> {
>>> if (firmware_has_feature(FW_FEATURE_LPAR) && !radix_enabled())
>>>          return false;
>>>
>>>      return true;
>>> }
>>>
>>>
>>> I am wondering whether it should be
>>>
>>> #define __HAVE_ARCH_GIGANTIC_PAGE_RUNTIME_SUPPORTED
>>> static inline bool gigantic_page_runtime_supported(void)
>>> {
>>>
>>>     if (!IS_ENABLED(CONFIG_CONTIG_ALLOC))
>>>          return false;
>> I don't think this test should happen here, CONFIG_CONTIG_ALLOC only allows
>> to allocate gigantic pages, doing that check here would prevent powerpc
>> to free boottime gigantic pages when not a guest. Note that this check
>> is actually done in set_max_huge_pages.
>>
>>
>>> if (firmware_has_feature(FW_FEATURE_LPAR) && !radix_enabled())
>>>          return false;
>> Maybe I did not understand this check: I understood that, in the case
>> the system
>> is virtualized, we do not want it to hand back gigantic pages. Does this
>> check
>> test if the system is currently being virtualized ?
>> If yes, I think the patch is correct: it prevents freeing gigantic pages
>> when the system
>> is virtualized but allows a 'normal' system to free gigantic pages.
>>
>>
> Ok double checked the patch applying the the tree. I got confused by the
> removal of that #ifdef. So we now disallow the runtime free by checking
> for gigantic_page_runtime_supported() in  __nr_hugepages_store_common.
> Now if we allow and if CONFIG_CONTIG_ALLOC is disabled, we still should
> allow to free the boot time allocated pages back to buddy.
>
> The patch looks good. You can add for the series
>
> Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
>
> -aneesh
>

Thanks for your time Aneesh,

Alex