linux-kernel - Re: [PATCH v4 07/10] powerpc/mm: Use generic_hugetlb_get_unmapped

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Date:   Thu, 16 Dec 2021 17:13:47 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Piggin <npiggin@...il.com>,
        "alex@...ti.fr" <alex@...ti.fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Steve Capper <steve.capper@....com>
CC:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 07/10] powerpc/mm: Use
 generic_hugetlb_get_unmapped_area()



Le 09/12/2021 à 11:02, Nicholas Piggin a écrit :
> Excerpts from Christophe Leroy's message of December 9, 2021 3:18 am:
>> Use the generic version of arch_hugetlb_get_unmapped_area()
>> which is now available at all time.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>>   arch/powerpc/include/asm/book3s/64/hugetlb.h |  4 --
>>   arch/powerpc/mm/book3s64/radix_hugetlbpage.c | 55 --------------------
>>   arch/powerpc/mm/hugetlbpage.c                |  4 +-
>>   3 files changed, 1 insertion(+), 62 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/book3s/64/hugetlb.h b/arch/powerpc/include/asm/book3s/64/hugetlb.h
>> index 12e150e615b7..b37a28f62cf6 100644
>> --- a/arch/powerpc/include/asm/book3s/64/hugetlb.h
>> +++ b/arch/powerpc/include/asm/book3s/64/hugetlb.h
>> @@ -8,10 +8,6 @@
>>    */
>>   void radix__flush_hugetlb_page(struct vm_area_struct *vma, unsigned long vmaddr);
>>   void radix__local_flush_hugetlb_page(struct vm_area_struct *vma, unsigned long vmaddr);
>> -extern unsigned long
>> -radix__hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>> -				unsigned long len, unsigned long pgoff,
>> -				unsigned long flags);
>>   
>>   extern void radix__huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
>>   						unsigned long addr, pte_t *ptep,
>> diff --git a/arch/powerpc/mm/book3s64/radix_hugetlbpage.c b/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
>> index 23d3e08911d3..d2fb776febb4 100644
>> --- a/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
>> +++ b/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
>> @@ -41,61 +41,6 @@ void radix__flush_hugetlb_tlb_range(struct vm_area_struct *vma, unsigned long st
>>   		radix__flush_tlb_range_psize(vma->vm_mm, start, end, psize);
>>   }
>>   
>> -/*
>> - * A vairant of hugetlb_get_unmapped_area doing topdown search
>> - * FIXME!! should we do as x86 does or non hugetlb area does ?
>> - * ie, use topdown or not based on mmap_is_legacy check ?
>> - */
>> -unsigned long
>> -radix__hugetlb_get_unmapped_area(struct file *file, unsigned long addr,
>> -				unsigned long len, unsigned long pgoff,
>> -				unsigned long flags)
>> -{
>> -	struct mm_struct *mm = current->mm;
>> -	struct vm_area_struct *vma;
>> -	struct hstate *h = hstate_file(file);
>> -	int fixed = (flags & MAP_FIXED);
>> -	unsigned long high_limit;
>> -	struct vm_unmapped_area_info info;
>> -
>> -	high_limit = DEFAULT_MAP_WINDOW;
>> -	if (addr >= high_limit || (fixed && (addr + len > high_limit)))
>> -		high_limit = TASK_SIZE;
> 
> I wonder if generic hugetlb_get_unmapped_area needs to have the
> arch_get_mmap_end() added.
> 
> arm64 has arch_get_mmap_end() and !HAVE_ARCH_HUGETLB_UNMAPPED_AREA so
> it looks like it has broken large address hint logic for hugetlbfs
> mappings? x86-64 defines their own and does the same hinting for
> normal and hugetlbfs mmap.
> 
> If we had that and defied arch_get_mmap_end(), then this patch should
> work.
> 

As far as I can see, hugetlb_get_unmapped_area() variants used to be 
very similar to get_unmapped_area() until commit 1be7107fbe18 ("mm: 
larger stack guard gap, between vmas") and commit f6795053dac8 ("mm: 
mmap: Allow for "high" userspace addresses")

I see no reason why those changes couldn't apply to 
hugetlb_get_unmapped_area() as well.

Need to know what ARM64 think about it thought. Will, Catalin, any opinion ?

Christophe