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Date: Thu, 28 Dec 2017 08:32:20 -0800
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Hyunchul Lee <hyc.lee@...il.com>
Cc: Chao Yu <yuchao0@...wei.com>, Chao Yu <chao@...nel.org>,
Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net, kernel-team@....com,
linux-fsdevel@...r.kernel.org, Hyunchul Lee <cheol.lee@....com>
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: pass down write hints to block
layer for bufferd write
On 12/28, Hyunchul Lee wrote:
> Hi Jaegeuk,
>
> On 12/28/2017 12:26 PM, Jaegeuk Kim wrote:
> > On 12/23, Chao Yu wrote:
> >> On 2017/12/15 10:06, Jaegeuk Kim wrote:
> >>> On 12/14, Hyunchul Lee wrote:
> >>>> Hi Jaegeuk,
> >>>>
> >>>> I need your comment about the fs_iohint mount option.
> >>>>
> >>>> a) w/o fs_iohint, propagate user hints to low layer.
> >>>> b) w/ fs_iohint, ignore user hints, and use hints which is generated
> >>>> with F2FS.
> >>>>
> >>>> Chao suggests this option. because user hints are more accurate than
> >>>> file system.
> >>>>
> >>>> This is resonable, But I have some concerns about this option.
> >>>> The first thing is that blocks of a segments have different hints. This
> >>>> could make GC less effective.
> >>>> The second is that the separation between LIFE_MEDIUM and LIFE_LONG is
> >>>> really needed. I think that difference between them is a little ambigous
> >>>> for users, and LIFE_SHORT and LIFE_EXTREME is converted to different
> >>>> hints by F2FS.
> >>>
> >>> I think what we really can do would assign many user hints to our 3 DATA
> >>> logs likewise rw_hint_to_seg_type(), since it's just hints for user data.
> >>> Then, we can decide how to keep that as much as possible, since we have
> >>> another filesystem metadata such as meta and nodes. In addition, I don't
> >>> think we have to keep the original user-hints which makes F2FS logs be
> >>> messed up.
> >>>
> >>> With that mind, I can think of the below cases. Especially, if user wants
> >>> to keep their io_hints, we'd better recommend to use direct_io w/o fs_iohints.
> >>
> >>
> >>
> >>> In order to keep this policy, I think fs_iohints would be better to be a
> >>> feature set by mkfs.f2fs and detected by sysfs entries for users.
> >>>
> >>> 1) w/ fs_iohints
> >>>
> >>> User F2FS Block
> >>> -------------------------------------------------------------------
> >>> Meta WRITE_LIFE_MEDIUM
> >>> HOT_NODE WRITE_LIFE_NOTSET
> >>> WARM_NODE -'
> >>> COLD_NODE WRITE_LIFE_NONE
> >>> ioctl(cold) COLD_DATA WRITE_LIFE_EXTREME
> >>> extention list -' -'
> >>> WRITE_LIFE_EXTREME -' -'
> >>> WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT
> >>>
> >>> -- buffered_io
> >>> WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_LONG
> >>> WRITE_LIFE_NONE -' -'
> >>> WRITE_LIFE_MEDIUM -' -'
> >>> WRITE_LIFE_LONG -' -'
> >>>
> >>> -- direct_io (Not recommendable)
> >>> WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET
> >>> WRITE_LIFE_NONE -' WRITE_LIFE_NONE
> >>> WRITE_LIFE_MEDIUM -' WRITE_LIFE_MEDIUM
> >>> WRITE_LIFE_LONG -' WRITE_LIFE_LONG
> >>
> >> Agreed with above IO hint mapping rule.
> >>
> >>>
> >>> 2) w/o fs_iohints
> >>>
> >>> User F2FS Block
> >>> -------------------------------------------------------------------
> >>> Meta -
> >>> HOT_NODE -
> >>> WARM_NODE -
> >>> COLD_NODE -
> >>> ioctl(cold) COLD_DATA -
> >>> extention list -' -
> >>>
> >>> -- buffered_io
> >>> WRITE_LIFE_EXTREME COLD_DATA -
> >>> WRITE_LIFE_SHORT HOT_DATA -
> >>> WRITE_LIFE_NOT_SET WARM_DATA -
> >>> WRITE_LIFE_NONE -' -
> >>> WRITE_LIFE_MEDIUM -' -
> >>> WRITE_LIFE_LONG -' -
> >>
> >> Now we recommend direct_io if user wants to give IO hint for storage, I suspect
> >> that user would suffer performance regression issue w/o buffered IO.
> >>
> >> Another problem is that, now, in Android, it will be very hard to prompt
> >> application to migrate their IO pattern from buffered IO to direct IO, one
> >> possible way is distinguishing user data lifetime from FWK, e.g. set
> >> WRITE_LIFE_SHORT for cache file or tmp file, set WRITE_LIFE_EXTREME for media file.
> >>
> >> In order to support buffered_io, would it be better to change mapping as below?
> >>
> >> -- buffered_io
> >> WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME
> >> WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT
> >> WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET
> >> WRITE_LIFE_NONE -' -'
> >> WRITE_LIFE_MEDIUM -' -'
> >> WRITE_LIFE_LONG -' -'
> >
> > Agreed, and it makes more sense that we'd better keep the write hints on
> > userdata given by applications.
> >
> > BTW, since we couldn't get any performance numbers with these, how about
> > adding a mount option like "-o iohints=MODE" where MODE may be one of
> > "fs-based", "user-based", and "off"?
> >
>
> "fs-based" equals "with fs_iohints", "user-based" equals "without fs_iohints"
> + Chao's suggest, and "off" means not passing down hints to block layer. right?
Yup, this'd allow us to add more options easily later.
Thanks,
>
> Thanks.
>
> > Thanks,
> >
> >>
> >> Thanks,
> >>
> >>>
> >>> -- direct_io
> >>> WRITE_LIFE_EXTREME COLD_DATA WRITE_LIFE_EXTREME
> >>> WRITE_LIFE_SHORT HOT_DATA WRITE_LIFE_SHORT
> >>> WRITE_LIFE_NOT_SET WARM_DATA WRITE_LIFE_NOT_SET
> >>> WRITE_LIFE_NONE -' WRITE_LIFE_NONE
> >>> WRITE_LIFE_MEDIUM -' WRITE_LIFE_MEDIUM
> >>> WRITE_LIFE_LONG -' WRITE_LIFE_LONG
> >>>
> >>>
> >>> Note that, I don't much care about how to manipulate streamid in nvme driver
> >>> in terms of LIFE_NONE or LIFE_NOTSET, since other drivers can handle them
> >>> in different ways. Taking a look at the definition, at least, we don't need
> >>> to assume that those are same at all. For example, if we can expolit this in
> >>> UFS driver, we can pass all the stream ids to the device as context ids.
> >>>
> >>> Thanks,
> >>>
> >>>>
> >>>> Thanks.
> >>>>
> >>>> On 12/12/2017 11:45 AM, Chao Yu wrote:
> >>>>> Hi Hyunchul,
> >>>>>
> >>>>> On 2017/12/12 10:15, Hyunchul Lee wrote:
> >>>>>> Hi Chao,
> >>>>>>
> >>>>>> On 12/11/2017 10:15 PM, Chao Yu wrote:
> >>>>>>> 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@....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.
> >>>>>>>
> >>>>>>
> >>>>>> Okay, I will implement this option and send this patch again.
> >>>>>
> >>>>> Let's wait for Jaegeuk's comments first?
> >>>>>
> >>>>>>
> >>>>>> Without fs_iohint, Even if data blocks are moved due to GC,
> >>>>>> we should keep user hints. And if user hints are not given,
> >>>>>> any hints are not passed down to block layer, right?
> >>>>>
> >>>>> Hmm.. that will be a problem, IMO, we can store last user's io_hint into inode
> >>>>> layout, so later when we trigger GC, we can use the last io_hint in inode rather
> >>>>> than giving no hint or fs' hint.
> >>>>>
> >>>>> I think it needs to discuss with original author of IO hint, what is the IO hint
> >>>>> policy when filesystem move block by itself after inode has been released in system.
> >>>>>
> >>>>> Thanks,
> >>>>>
> >>>>>>
> >>>>>> Thank you for comments.
> >>>>>>
> >>>>>>> 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,
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>
> >>>>>>>> ------------------------------------------------------------------------------
> >>>>>>>> Check out the vibrant tech community on one of the world's most
> >>>>>>>> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> >>>>>>>> _______________________________________________
> >>>>>>>> Linux-f2fs-devel mailing list
> >>>>>>>> Linux-f2fs-devel@...ts.sourceforge.net
> >>>>>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> >>>>>>>>
> >>>>>>>
> >>>>>>
> >>>>>> .
> >>>>>>
> >>>>>
> >>>>>
> >>>>> ------------------------------------------------------------------------------
> >>>>> Check out the vibrant tech community on one of the world's most
> >>>>> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> >>>>> _______________________________________________
> >>>>> Linux-f2fs-devel mailing list
> >>>>> Linux-f2fs-devel@...ts.sourceforge.net
> >>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> >>>>>
> >>>
> >>> .
> >>>
> >
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