From: Hushijie <hushijie3@huawei.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: "will@kernel.org" <will@kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Nixiaoming <nixiaoming@huawei.com>,
"wangxu (AE)" <wangxu72@huawei.com>,
"Wangkefeng (OS Kernel Lab)" <wangkefeng.wang@huawei.com>,
yangerkun <yangerkun@huawei.com>,
"Wangle (RTOS FAE)" <wangle6@huawei.com>,
"Chengang (L)" <cg.chen@huawei.com>,
"Chenjie (K)" <chenjie6@huawei.com>,
"Huangjianhui (Alex)" <alex.huangjianhui@huawei.com>
Subject: Re: [PATCH v5] hugetlbfs: Get unmapped area below TASK_UNMAPPED_BASE for hugetlbfs
Date: Mon, 18 May 2020 06:23:26 +0000 [thread overview]
Message-ID: <c27a402512b84ce598420b28f525eb75@huawei.com> (raw)
>On 5/16/20 12:47 AM, Hushijie wrote:
>>> On 5/14/20 7:31 AM, Shijie Hu wrote:
>>>> + if (mm->get_unmapped_area == arch_get_unmapped_area)
>>>> + return hugetlb_get_unmapped_area_bottomup(file, addr, len,
>>>> + pgoff, flags);
>>>> + return hugetlb_get_unmapped_area_topdown(file, addr, len,
>>>> + pgoff, flags);
>>>
>>> I like this code using the value of mm->get_unmapped_area to determine
>>> which routine to call. It is used by a few architectures. However, I
>>> noticed that on at least one architecture (powerpc) mm->get_unmapped_area
>>> may be assigned to routines other than arch_get_unmapped_area or
>>> arch_get_unmapped_area_topdown. In such a case, we would call the 'new'
>>> topdown routine. I would prefer that we call the bottomup routine in this
>>> default case.
>>>
>>> In reality, this does not impact powerpc as that architecture has it's
>>> own hugetlb_get_unmapped_area routine.
>>>
>>
>> Yes, I also noticed this before, powerpc uses radix__arch_get_unmapped_area*()
>> when CONFIG_PPC_RADIX_MMU opened as 'y' and radix_enabled() returns
>> true. However, powerpc implemented its own hugetlb_get_unmapped_area(). This
>> patch actually has no effect on powerpc.
>>
>>> Because of this, I suggest we add a comment above this code and switch
>>> the if/else order. For example,
>>>
>>> + /*
>>> + * Use mm->get_unmapped_area value as a hint to use topdown routine.
>>> + * If architectures have special needs, they should define their own
>>> + * version of hugetlb_get_unmapped_area.
>>> + */
>>> + if (mm->get_unmapped_area == arch_get_unmapped_area_topdown)
>>> + return hugetlb_get_unmapped_area_topdown(file, addr, len,
>>> + pgoff, flags);
>>> + return hugetlb_get_unmapped_area_bottomup(file, addr, len,
>>> + pgoff, flags);
>>>
>>> Thoughts?
>>> --
>>> Mike Kravetz
>>>
>> I agree with you. It's clever to switch the if/else order. If there is such
>> a case, mm->get_unmapped_area() is neihter arch_get_unmapped_area() nor
>> arch_get_unmapped_area_topdown(), it is indeed more appropriate to make the
>> bottomup routine as the default behavior.
>>
>> May I put this code and comment you show above into patch v6 and add
>> "Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>" to it?
>
>Feel free to add this code and my Signed-off-by.
>
>I assume this still works for your use case. Correct?
>--
>Mike Kravetz
>
Yes, It still works for our use case.
Thanks for your replies and suggestions, I will submit patch v6 later.
--
Shijie Hu
next reply other threads:[~2020-05-18 6:23 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-18 6:23 Hushijie [this message]
-- strict thread matches above, loose matches on Subject: below --
2020-05-16 7:47 [PATCH v5] hugetlbfs: Get unmapped area below TASK_UNMAPPED_BASE for hugetlbfs Hushijie
2020-05-18 4:16 ` Mike Kravetz
2020-05-14 14:31 Shijie Hu
2020-05-15 18:44 ` Mike Kravetz
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