linux-kernel - Re: [PATCH v3 2/2] powerpc/mm/hugetlb: Add support for 1G huge pages

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Date:   Thu, 18 May 2017 14:20:24 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>, akpm@...ux-foundation.org,
        Anshuman Khandual <khandual@...ux.vnet.ibm.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 2/2] powerpc/mm/hugetlb: Add support for 1G huge pages



On Thursday 18 May 2017 02:17 PM, Michael Ellerman wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> writes:
> 
>> On Thursday 18 May 2017 10:51 AM, Michael Ellerman wrote:
>>> "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> writes:
>>>
>>>> POWER9 supports hugepages of size 2M and 1G in radix MMU mode. This patch
>>>> enables the usage of 1G page size for hugetlbfs. This also update the helper
>>>> such we can do 1G page allocation at runtime.
>>>>
>>>> We still don't enable 1G page size on DD1 version. This is to avoid doing
>>>> workaround mentioned in commit: 6d3a0379ebdc8 (powerpc/mm: Add
>>>> radix__tlb_flush_pte_p9_dd1()
>>>>
>>>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
>>>> ---
>>>>    arch/powerpc/include/asm/book3s/64/hugetlb.h | 10 ++++++++++
>>>>    arch/powerpc/mm/hugetlbpage.c                |  7 +++++--
>>>>    arch/powerpc/platforms/Kconfig.cputype       |  1 +
>>>>    3 files changed, 16 insertions(+), 2 deletions(-)
>>>
>>> I think this patch is OK, but it's very confusing because it doesn't
>>> mention that it's only talking about *generic* gigantic page support.
>>
>> What you mean by generic gigantic page ? what is supported here is the
>> gigantic page with size 1G alone ?
> 
> What about 16G pages on pseries.
> 
> And all the other gigantic page sizes that Book3E supports?
> 

None of that is supported w.r.t runtime allocation of hugepages. ie, we 
cannot echo nr_hugepages w.r.t them.  For 16GB i am not sure it make 
sense, because we will rarely get such large contiguous region. W.r.t 
page size supported for Book3E, may be we can. But I don't have a 
facility to test those. Hence didn't include that.

-aneesh