linux-kernel - Re: [PATCH v3 5/5] powerpc/mm: Fix growth direction for hugepages mmaps with slice

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Message-ID: <c532efa7-33a4-1f4f-e83a-5eaeba65b799@c-s.fr>
Date:   Wed, 24 Jan 2018 10:27:33 +0100
From:   Christophe LEROY <christophe.leroy@....fr>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Scott Wood <oss@...error.net>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 5/5] powerpc/mm: Fix growth direction for hugepages
 mmaps with slice



Le 24/01/2018 à 10:15, Aneesh Kumar K.V a écrit :
> 
> 
> On 01/24/2018 02:32 PM, Christophe Leroy wrote:
>> An application running with libhugetlbfs fails to allocate
>> additional pages to HEAP due to the hugemap being done
>> inconditionally as topdown mapping:
>>
>> mmap(0x10080000, 1572864, PROT_READ|PROT_WRITE, 
>> MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0) = 0x73e80000
>> [...]
>> mmap(0x74000000, 1048576, PROT_READ|PROT_WRITE, 
>> MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0x180000) = 0x73d80000
>> munmap(0x73d80000, 1048576)             = 0
>> [...]
>> mmap(0x74000000, 1572864, PROT_READ|PROT_WRITE, 
>> MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0x180000) = 0x73d00000
>> munmap(0x73d00000, 1572864)             = 0
>> [...]
>> mmap(0x74000000, 1572864, PROT_READ|PROT_WRITE, 
>> MAP_PRIVATE|MAP_ANONYMOUS|0x40000, -1, 0x180000) = 0x73d00000
>> munmap(0x73d00000, 1572864)             = 0
>> [...]
>>
>> As one can see from the above strace log, mmap() allocates further
>> pages below the initial one because no space is available on top of it.
>>
>> This patch fixes it by requesting bottomup mapping as the non
>> generic hugetlb_get_unmapped_area() does
>>
>> Fixes: d0f13e3c20b6f ("[POWERPC] Introduce address space "slices" ")
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> ---
>>   v3: Was a standalone patch before, but conflicts with this serie.
>>
>>   arch/powerpc/mm/hugetlbpage.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/powerpc/mm/hugetlbpage.c 
>> b/arch/powerpc/mm/hugetlbpage.c
>> index 79e1378ee303..368ea6b248ad 100644
>> --- a/arch/powerpc/mm/hugetlbpage.c
>> +++ b/arch/powerpc/mm/hugetlbpage.c
>> @@ -558,7 +558,7 @@ unsigned long hugetlb_get_unmapped_area(struct 
>> file *file, unsigned long addr,
>>           return radix__hugetlb_get_unmapped_area(file, addr, len,
>>                                  pgoff, flags);
>>   #endif
>> -    return slice_get_unmapped_area(addr, len, flags, mmu_psize, 1);
>> +    return slice_get_unmapped_area(addr, len, flags, mmu_psize, 0);
>>   }
>>   #endif
> 
> Why make this change also for PPC64? Can you do this #ifdef 8xx?.You can 
> ideally move hugetlb_get_unmapped_area to slice.h and then make this 
> much simpler for 8xxx?
> 

Did you try with HUGETLB_MORECORE_HEAPBASE=0x11000000 on PPC64 as I 
suggested in my last email on this subject (22/01/2018 9:22) ?

Before doing anything specific to the PPC32/8xx, I'd like to be sure the 
issue is definitly only on PPC32.

Thanks,
Christophe