Re: [PATCH] mm/thp: fix comments in transparent_hugepage_flags

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

Hi Jianguo,
On Thu, Sep 05, 2013 at 11:54:00AM +0800, Jianguo Wu wrote:
>On 2013/9/5 11:37, Wanpeng Li wrote:
>
>> On Thu, Sep 05, 2013 at 11:04:22AM +0800, Jianguo Wu wrote:
>>> Hi Wanpeng,
>>>
>>> On 2013/9/5 10:11, Wanpeng Li wrote:
>>>
>>>> Hi Jianguo,
>>>> On Wed, Sep 04, 2013 at 09:30:22PM +0800, Jianguo Wu wrote:
>>>>> Since commit d39d33c332(thp: enable direct defrag), defrag is enable
>>>>> for all transparent hugepage page faults by default, not only in
>>>>> MADV_HUGEPAGE regions.
>>>>>
>>>>> Signed-off-by: Jianguo Wu <wujianguo@huawei.com>
>>>>> ---
>>>>> mm/huge_memory.c | 6 ++----
>>>>> 1 file changed, 2 insertions(+), 4 deletions(-)
>>>>>
>>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>>>> index a92012a..abf047e 100644
>>>>> --- a/mm/huge_memory.c
>>>>> +++ b/mm/huge_memory.c
>>>>> @@ -28,10 +28,8 @@
>>>>>
>>>>> /*
>>>>>  * By default transparent hugepage support is enabled for all mappings
>>>>
>>>> This is also stale. TRANSPARENT_HUGEPAGE_ALWAYS is not configured by default in
>>>> order that avoid to risk increase the memory footprint of applications w/o a 
>>>> guaranteed benefit.
>>>>
>>>
>>> Right, how about this:
>>>
>>> By default transparent hugepage support is disabled in order that avoid to risk
>> 
>> I don't think it's disabled. TRANSPARENT_HUGEPAGE_MADVISE is configured
>> by default.
>> 
>
>Hi Wanpeng,
>
>We have TRANSPARENT_HUGEPAGE and TRANSPARENT_HUGEPAGE_ALWAYS/TRANSPARENT_HUGEPAGE_MADVISE,
>TRANSPARENT_HUGEPAGE_ALWAYS or TRANSPARENT_HUGEPAGE_MADVISE is configured only if TRANSPARENT_HUGEPAGE
>is configured.
>
>By default, TRANSPARENT_HUGEPAGE=n, and TRANSPARENT_HUGEPAGE_ALWAYS is configured when TRANSPARENT_HUGEPAGE=y.
>
>commit 13ece886d9(thp: transparent hugepage config choice):
>
> config TRANSPARENT_HUGEPAGE
>-       bool "Transparent Hugepage Support" if EMBEDDED
>+       bool "Transparent Hugepage Support"
>        depends on X86 && MMU
>-       default y
>
>+choice
>+       prompt "Transparent Hugepage Support sysfs defaults"
>+       depends on TRANSPARENT_HUGEPAGE
>+       default TRANSPARENT_HUGEPAGE_ALWAYS
>

mmotm tree:

grep 'TRANSPARENT_HUGEPAGE' .config
CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE=y
CONFIG_TRANSPARENT_HUGEPAGE=y
# CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS is not set
CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y

distro:

grep 'TRANSPARENT_HUGEPAGE' config-3.8.0-26-generic 
CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE=y
CONFIG_TRANSPARENT_HUGEPAGE=y
# CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS is not set
CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y


>Thanks,
>Jianguo Wu
>
>> Regards,
>> Wanpeng Li 
>> 
>>> increase the memory footprint of applications w/o a guaranteed benefit, and
>>> khugepaged scans all mappings when transparent hugepage enabled.
>>> Defrag is invoked by khugepaged hugepage allocations and by page faults for all
>>> hugepage allocations.
>>>
>>> Thanks,
>>> Jianguo Wu
>>>
>>>> Regards,
>>>> Wanpeng Li 
>>>>
>>>>> - * and khugepaged scans all mappings. Defrag is only invoked by
>>>>> - * khugepaged hugepage allocations and by page faults inside
>>>>> - * MADV_HUGEPAGE regions to avoid the risk of slowing down short lived
>>>>> - * allocations.
>>>>> + * and khugepaged scans all mappings. Defrag is invoked by khugepaged
>>>>> + * hugepage allocations and by page faults for all hugepage allocations.
>>>>>  */
>>>>> unsigned long transparent_hugepage_flags __read_mostly =
>>>>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
>>>>> -- 
>>>>> 1.8.1.2
>>>>>
>>>>> --
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>>>>
>>>
>>>
>> 
>> 
>> .
>> 
>
>

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