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Subject: Re: [PATCH v3 5/5] powerpc/mm: Fix growth direction for hugepages
 mmaps with slice
To:     Christophe Leroy <christophe.leroy@c-s.fr>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Scott Wood <oss@buserror.net>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <6920f6efe2dcdabf59350b2d31ee6bd4bdef57f4.1516783089.git.christophe.leroy@c-s.fr>
 <362a93307a09b521878c47a8999a39a228184293.1516783089.git.christophe.leroy@c-s.fr>
From:   "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Date:   Wed, 24 Jan 2018 14:45:12 +0530
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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@c-s.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?

-aneesh

-aneesh