... > >>>>>>>>>>>>>>> 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? > > > > What I am worried about is that datas with no hint have WRITE_LIFE_NOT_SET(id 0). > If block devices have swap partitions and anothor file systems, cold datas could > be mixed with datas from that. Does this seems way too much? That seems like how to distinguish write_hints across multiple partitions? > And I think that stream id 0 means disabling stream directives. > Becasue NVME_RW_DTYPE_STREAMS is clear. Then, I guess SSD FW will just handle 5 stream IDs including disabled 0. Thanks,
