Re: [RFC PATCH 0/2] apply write hints to select the type of segments

From: Hyunchul Lee
Date: Sun Nov 12 2017 - 20:35:22 EST


On 11/13/2017 10:26 AM, Chao Yu wrote:
> On 2017/11/13 8:24, Hyunchul Lee wrote:
>> On 11/10/2017 03:42 PM, Chao Yu wrote:
>>> On 2017/11/10 8:23, Hyunchul Lee wrote:
>>>> Hello, Chao
>>>>
>>>> On 11/09/2017 06:12 PM, Chao Yu wrote:
>>>>> On 2017/11/9 13:51, Hyunchul Lee wrote:
>>>>>> From: Hyunchul Lee <cheol.lee@xxxxxxx>
>>>>>>
>>>>>> Using write hints[1], applications can inform the life time of the data
>>>>>> written to devices. and this[2] reported that the write hints patch
>>>>>> decreased writes in NAND by 25%.
>>>>>>
>>>>>> This hints help F2FS to determine the followings.
>>>>>> 1) the segment types where the data will be written.
>>>>>> 2) the hints that will be passed down to devices with the data of segments.
>>>>>>
>>>>>> This patch set implements the first mapping from write hints to segment types
>>>>>> as shown below.
>>>>>>
>>>>>> hints segment type
>>>>>> ----- ------------
>>>>>> WRITE_LIFE_SHORT CURSEG_COLD_DATA
>>>>>> WRITE_LIFE_EXTREME CURSEG_HOT_DATA
>>>>>> others CURSEG_WARM_DATA
>>>>>>
>>>>>> The F2FS poliy for hot/cold seperation has precedence over this hints, And
>>>>>> hints are not applied in in-place update.
>>>>>
>>>>> Could we change to disable IPU if file/inode write hint is existing?
>>>>>
>>>>
>>>> I am afraid that this makes side effects. for example, this could cause
>>>> out-of-place updates even when there are not enough free segments.
>>>> I can write the patch that handles these situations. But I wonder
>>>> that this is required, and I am not sure which IPU polices can be disabled.
>>>
>>> Oh, As I replied in another thread, I think IPU just affects filesystem
>>> hot/cold separating, rather than this feature. So I think it will be okay
>>> to not consider it.
>>>
>>>>
>>>>>>
>>>>>> Before the second mapping is implemented, write hints are not passed down
>>>>>> to devices. Because it is better that the data of a segment have the same
>>>>>> hint.
>>>>>>
>>>>>> [1]: c75b1d9421f80f4143e389d2d50ddfc8a28c8c35
>>>>>> [2]: https://lwn.net/Articles/726477/
>>>>>
>>>>> Could you write a patch to support passing write hint to block layer for
>>>>> buffered writes as below commit:
>>>>> 0127251c45ae ("ext4: add support for passing in write hints for buffered writes")
>>>>>
>>>>
>>>> Sure I will. I wrote it already ;)
>>>
>>> Cool, ;)
>>>
>>>> I think that datas from the same segment should be passed down with the same
>>>> hint, and the following mapping is reasonable. I wonder what is your opinion
>>>> about it.
>>>>
>>>> segment type hints
>>>> ------------ -----
>>>> CURSEG_COLD_DATA WRITE_LIFE_EXTREME
>>>> CURSEG_HOT_DATA WRITE_LIFE_SHORT
>>>> CURSEG_COLD_NODE WRITE_LIFE_NORMAL
>>>
>>> We have WRITE_LIFE_LONG defined rather than WRITE_LIFE_NORMAL in fs.h?
>>>
>>>> CURSEG_HOT_NODE WRITE_LIFE_MEDIUM
>>>
>>> As I know, in scenario of cell phone, data of meta_inode is hottest, then hot
>>> data, warm node, and cold node should be coldest. So I suggested we can define
>>> as below:
>>>
>>> META_DATA WRITE_LIFE_SHORT
>>> HOT_DATA & WARM_NODE WRITE_LIFE_MEDIUM
>>> HOT_NODE & WARM_DATA WRITE_LIFE_LONG
>>> COLD_NODE & COLD_DATA WRITE_LIFE_EXTREME
>>>
>>
>> I agree, But I am not sure that assigning the same hint to a node and data
>> segment is good. Because NVMe is likely to write them in the same erase
>> block if they have the same hint.
>
> If we do not give the hint, they can still be written to the same erase block,
> right? it will not be worse?
>

If the hint is not given, I think that they could be written to
the same erase block, or not. But if we give the same hint, they are written
to the same block.
I am not sure ;)

> Thanks,
>
>>
>> Thanks.
>>
>>> Thanks,
>>>
>>>> others WRITE_LIFE_NONE
>>>>
>>>>> Thanks,
>>>>>
>>>>>>
>>>>>> Hyunchul Lee (2):
>>>>>> f2fs: apply write hints to select the type of segments for buffered
>>>>>> write
>>>>>> f2fs: apply write hints to select the type of segment for direct write
>>>>>>
>>>>>> fs/f2fs/data.c | 101 ++++++++++++++++++++++++++++++++----------------------
>>>>>> fs/f2fs/f2fs.h | 1 +
>>>>>> fs/f2fs/segment.c | 14 +++++++-
>>>>>> 3 files changed, 74 insertions(+), 42 deletions(-)
>>>>>>
>>>>>
>>>>>
>>>>
>>>> Thanks
>>>>
>>>> .
>>>>
>>>
>>>
>>
>> .
>>
>
>