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From:   "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To:     Alexandre Ghiti <alex@ghiti.fr>, mpe@ellerman.id.au,
        Andrew Morton <akpm@linux-foundation.org>,
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Subject: Re: [PATCH v8 4/4] hugetlb: allow to free gigantic pages regardless of the configuration
In-Reply-To: <e7637427-5f17-b4f4-93a2-70cac9b3a264@ghiti.fr>
References: <20190327063626.18421-1-alex@ghiti.fr> <20190327063626.18421-5-alex@ghiti.fr> <f6e74ad8-acca-3b1e-27eb-a2881ac8437d@linux.ibm.com> <fbae7220-2e6f-8516-cf93-fbe430452043@ghiti.fr> <aabfc780-1681-c69a-9927-4645d6499984@linux.ibm.com> <e7637427-5f17-b4f4-93a2-70cac9b3a264@ghiti.fr>
Date:   Wed, 27 Mar 2019 15:35:13 +0530
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Alexandre Ghiti <alex@ghiti.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@linux.ibm.com>

-aneesh