Subject: Re: [PATCH v2] 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: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
References: <20180109101810.2471D6C6CF@localhost.localdomain>
 <87wp0haizf.fsf@linux.vnet.ibm.com>
 <d5f6060f-3061-dc3c-66f7-3cec05d50169@c-s.fr>
From: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Date: Wed, 17 Jan 2018 08:49:03 +0530
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On 01/16/2018 10:18 PM, Christophe LEROY wrote:
> 
> 
> Le 16/01/2018 à 17:03, Aneesh Kumar K.V a écrit :
>> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>>
>>> 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
>>> [...]
>>>
>>
>> Can you explain the failure details above. I am not sure I understand
>> what to read from the above output.
> 
> libhugetlbfs first requests an area of size 1.5Mbytes, at address 
> 0x10080000
> mmap() returns an area at address 0x73e80000
> 
> Then libhugetlbfs requests an additional area on top of that, ie at 
> address 0x74000000, to expand the heap.
> But mmap() returns an area at address 0x73d80000, ie under the previous 
> area.
> 


Can you share the test details?. Why does it not fail on book3s64? We 
use topdown search with book3s64.

> This is not the behaviour when using the generic (ie without mm_slices) 
> hugepages code, and this is not what libhugetlbfs expects for expending 
> the heap.
> 
>

-aneesh