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

[Jaegeuk Kim]

On 11/16, Chao Yu wrote:
> On 2017/11/16 8:56, Hyunchul Lee wrote:
> > 
> > On 11/16/2017 01:27 AM, Jaegeuk Kim wrote:
> >> On 11/14, Chao Yu wrote:
> >>> On 2017/11/14 12:20, Jaegeuk Kim wrote:
> >>>> On 11/13, Hyunchul Lee wrote:
> >>>>> On 11/13/2017 10:59 AM, Chao Yu wrote:
> >>>>>> On 2017/11/13 9:35, Hyunchul Lee wrote:
> >>>>>>> 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,
> >>>>>>
> >>>>>> I mean it's possible to write them 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.
> >>>>>>
> >>>>>> IMO, Only if underlying device can support more hint type or opened channels,
> >>>>>> and actual temperature of data segment and node segment is quite different, we
> >>>>>> can separate them.
> >>>>>>
> >>>>>
> >>>>> Okay, If Jaegeuk Kim agrees with this, I will submit the patch that 
> >>>>> implements your proposed mapping.
> >>>>
> >>>> How about this? We'd better to split data and node blocks as much as possible.
> >>>>
> >>>> segment type                    hints
> >>>> ------------                    -----
> >>>> COLD_NODE & COLD_DATA		WRITE_LIFE_NONE
> >>>
> >>> WRITE_LIFE_NONE means there is no hints about write life time.
> >>>
> >>> Shouldn't we define COLD_NODE & COLD_DATA as WRITE_LIFE_EXTERME?
> >>
> >> The assumption would be to split different types of blocks by flash firmware,
> >> so I think we can use WRITE_LIFE_NONE as a type as well.
> >>
> > 
> > WRITE_LIFE_NONE means that no stream id is specified. It equals WRITE_LIFE_NOT_SET.
> 
> Rgith, I just saw nvme implementation:
> 
> nvme_assign_write_stream
> 
> 	enum rw_hint streamid = req->write_hint;
> 
> 	if (streamid == WRITE_LIFE_NOT_SET || streamid == WRITE_LIFE_NONE)
> 		streamid = 0;
> 	else {
> 		streamid--;
> ...
> 
> > So I think that we can define WARM_DATA as WRITE_LIFE_NONE, and
> > COLD_NODE & COLD_DATA as WRITE_LIFE_EXTREME.

What's the point?

segment type                 hints                streamid
-------------                -----                -------
COLD_NODE & COLD_DATA        WRITE_LIFE_NONE      0
WARM_DATA                    WRITE_LIFE_EXTERME   4
HOT_NODE & WARM_NODE         WRITE_LIFE_LONG      3
HOT_DATA                     WRITE_LIFE_MEDIUM    2
META_DATA                    WRITE_LIFE_SHORT     1

So, I don't think something is wrong. Again, I don't care about its hotness
given to the naming, but do care how to split different types of blocks with
different stream ids. Exceptions would be giving _SHORT or _MEDIUM which are
likely to be latency-critical, since I guess firmware may be able to store them
into SLC buffer.

Am I missing that _NONE has another meaning?

Thanks,

> 
> I think that would be better.
> 
> Thanks,
> 
> > 
> > Thanks.
> > 
> >> Thanks,
> >>
> >>>
> >>> Thanks,
> >>>
> >>>> WARM_DATA			WRITE_LIFE_EXTERME
> >>>> HOT_NODE & WARM_NODE		WRITE_LIFE_LONG
> >>>> HOT_DATA			WRITE_LIFE_MEDIUM
> >>>> META_DATA			WRITE_LIFE_SHORT
> >>>>
> >>>>>
> >>>>> Thank you for comments ;)
> >>>>>
> >>>>>> Thanks,
> >>>>>>
> >>>>>>> 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
> >>>>>>>>>>>
> >>>>>>>>>>> .
> >>>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>>
> >>>>>>>>>
> >>>>>>>>> .
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>>
> >>>>>>>
> >>>>>>> .
> >>>>>>>
> >>>>>>
> >>>>>>
> >>>>
> >>>> .
> >>>>
> >>
> > 
> > .
> >