linux-kernel - Re: [RFC PATCH v2 2/2] arm64 Kconfig: Select gigantic page

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Date:   Mon, 22 Aug 2016 19:33:46 +0800
From:   Yisheng Xie <xieyisheng1@...wei.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Michal Hocko <mhocko@...nel.org>
CC:     <mark.rutland@....com>, <linux-mm@...ck.org>,
        <sudeep.holla@....com>, <will.deacon@....com>,
        <linux-kernel@...r.kernel.org>, <dave.hansen@...el.com>,
        <robh+dt@...nel.org>, <guohanjun@...wei.com>,
        <akpm@...ux-foundation.org>, <n-horiguchi@...jp.nec.com>,
        <linux-arm-kernel@...ts.infradead.org>, <mike.kravetz@...cle.com>
Subject: Re: [RFC PATCH v2 2/2] arm64 Kconfig: Select gigantic page



On 2016/8/22 18:00, Catalin Marinas wrote:
> On Mon, Aug 22, 2016 at 10:03:58AM +0200, Michal Hocko wrote:
>> On Mon 22-08-16 10:56:43, Xie Yisheng wrote:
>>> Arm64 supports gigantic page after
>>> commit 084bd29810a5 ("ARM64: mm: HugeTLB support.")
>>> however, it got broken by 
>>> commit 944d9fec8d7a ("hugetlb: add support for gigantic page
>>> allocation at runtime")
>>>
>>> This patch selects ARCH_HAS_GIGANTIC_PAGE to make this
>>> function can be used again.
>>
>> I haven't double checked that the above commit really broke it but if
>> that is the case then
>>  
>> Fixes: 944d9fec8d7a ("hugetlb: add support for gigantic page allocation at runtime")
>>
>> would be nice as well I guess. I do not think that marking it for stable
>> is really necessary considering how long it's been broken and nobody has
>> noticed...
> 
> I'm not sure that commit broke it. The gigantic functionality introduced
> by the above commit was under an #ifdef CONFIG_X86_64. Prior
> to that we had a VM_BUG_ON(hstate_is_gigantic(h)).
> 
Hi Catalin and Michal ,
Thank you for your reply.
Before that commit gigantic pages can only be allocated at boottime and
can't be freed. That why we had VM_BUG_ON(hstate_is_gigantic(h)) in
function update_and_free_page() Prior to that.

Anyway, it should not just add #ifdef CONFIG_X86_64 for arm64 already
supported 1G hugepage before that commit. Right?

Please let me know if I miss something.

Thanks
Xie Yisheng.