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

Jianguo Wu
2013-09-05T03:58:24Z

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

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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>>>
>>
>>
>
>
> .
>