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SubjectRe: [f2fs-dev] [PATCH 1/2] f2fs: pass down write hints to block layer for bufferd write
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Hi Hyunchul,

On 2017/12/1 16:28, Hyunchul Lee wrote:
> Hi Chao,
>
> On 11/30/2017 04:06 PM, Chao Yu wrote:
>> Hi Hyunchul,
>>
>> On 2017/11/28 8:23, Hyunchul Lee wrote:
>>> From: Hyunchul Lee <cheol.lee@lge.com>
>>>
>>> This implements which hint is passed down to block layer
>>> for datas from the specific segment type.
>>>
>>> segment type hints
>>> ------------ -----
>>> COLD_NODE & COLD_DATA WRITE_LIFE_EXTREME
>>> WARM_DATA WRITE_LIFE_NONE
>>> HOT_NODE & WARM_NODE WRITE_LIFE_LONG
>>> HOT_DATA WRITE_LIFE_MEDIUM
>>> META_DATA WRITE_LIFE_SHORT
>>
>> Just noticed, if our user do not give the hint via ioctl, f2fs can
>> provider hint to lower layer according to hot/cold separation ability,
>> it will be okay. But once user give his hint which may be more accurate
>> than filesystem, hint converted by f2fs may be wrong.
>>
>> So what do you think of adding an option to control whether filesystem
>> can convert hint user given?
>>
>
> I think it is okay for LIFE_SHORT and LIFE_EXTREME. because they are
> converted to different hints.

What I mean is introducing a mount option, e.g. fs_iohint,
a) w/o fs_iohint, propagate file/inode io_hint to low layer.
b) w/ fs_iohint, ignore file/inode io_hint, use io_hint which is generated
with filesystem's private rule.

Thanks,

>
> file hint segment type io hint
> --------- ------------ -------
> LIFE_SHORT HOT_DATA LIFE_MEDIUM
> LIFE_MEDIUM WARM_DATA LIFE_NONE
> LIFE_LONG WARM_DATA LIFE_NONE
> LIFE_EXTREME COLD_DATA LIFE_EXTREME
>
> the problem is that LIFE_MEDIUM and LIFE_LONG are converted to
> the same hint, LIFE_NONE. I am not sure that the seperation between
> LIFE_MEDIUM and LIFE_LONG is really needed. Because I guess that the
> difference between them is a little ambigous for users, and if WARM_DATA
> segment has two different hints, it can makes GC non-efficient.
>
> I wonder your thought about this.
>
> Thanks.
>
>> Thanks,
>>
>>
>
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