Date:	Mon, 08 Oct 2012 21:11:45 +0900
From:	Jaegeuk Kim <jaegeuk.kim@...sung.com>
To:	'Namjae Jeon' <linkinjeon@...il.com>
Cc:	'Vyacheslav Dubeyko' <slava@...eyko.com>,
	'Marco Stornelli' <marco.stornelli@...il.com>,
	'Jaegeuk Kim' <jaegeuk.kim@...il.com>,
	'Al Viro' <viro@...iv.linux.org.uk>, tytso@....edu,
	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	chur.lee@...sung.com, cm224.lee@...sung.com,
	jooyoung.hwang@...sung.com, linux-fsdevel@...r.kernel.org
Subject: RE: [PATCH 00/16] f2fs: introduce flash-friendly file system

> -----Original Message-----
> From: Namjae Jeon [mailto:linkinjeon@...il.com]
> Sent: Monday, October 08, 2012 8:22 PM
> To: Jaegeuk Kim
> Cc: Vyacheslav Dubeyko; Marco Stornelli; Jaegeuk Kim; Al Viro; tytso@....edu;
> gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org; chur.lee@...sung.com; cm224.lee@...sung.com;
> jooyoung.hwang@...sung.com; linux-fsdevel@...r.kernel.org
> Subject: Re: [PATCH 00/16] f2fs: introduce flash-friendly file system
> 
> 2012/10/8, Jaegeuk Kim <jaegeuk.kim@...sung.com>:
> >> -----Original Message-----
> >> From: Namjae Jeon [mailto:linkinjeon@...il.com]
> >> Sent: Monday, October 08, 2012 7:00 PM
> >> To: Jaegeuk Kim
> >> Cc: Vyacheslav Dubeyko; Marco Stornelli; Jaegeuk Kim; Al Viro;
> >> tytso@....edu;
> >> gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> >> chur.lee@...sung.com; cm224.lee@...sung.com;
> >> jooyoung.hwang@...sung.com; linux-fsdevel@...r.kernel.org
> >> Subject: Re: [PATCH 00/16] f2fs: introduce flash-friendly file system
> >>
> >> 2012/10/8, Jaegeuk Kim <jaegeuk.kim@...sung.com>:
> >> >> -----Original Message-----
> >> >> From: Vyacheslav Dubeyko [mailto:slava@...eyko.com]
> >> >> Sent: Sunday, October 07, 2012 9:09 PM
> >> >> To: Jaegeuk Kim
> >> >> Cc: 'Marco Stornelli'; 'Jaegeuk Kim'; 'Al Viro'; tytso@....edu;
> >> >> gregkh@...uxfoundation.org; linux-
> >> >> kernel@...r.kernel.org; chur.lee@...sung.com; cm224.lee@...sung.com;
> >> >> jooyoung.hwang@...sung.com;
> >> >> linux-fsdevel@...r.kernel.org
> >> >> Subject: Re: [PATCH 00/16] f2fs: introduce flash-friendly file system
> >> >>
> >> >> Hi,
> >> >>
> >> >> On Oct 7, 2012, at 1:31 PM, Jaegeuk Kim wrote:
> >> >>
> >> >> >> -----Original Message-----
> >> >> >> From: Marco Stornelli [mailto:marco.stornelli@...il.com]
> >> >> >> Sent: Sunday, October 07, 2012 4:10 PM
> >> >> >> To: Jaegeuk Kim
> >> >> >> Cc: Vyacheslav Dubeyko; jaegeuk.kim@...sung.com; Al Viro;
> >> >> >> tytso@....edu; gregkh@...uxfoundation.org;
> >> >> >> linux-kernel@...r.kernel.org; chur.lee@...sung.com;
> >> >> >> cm224.lee@...sung.com;
> >> >> jooyoung.hwang@...sung.com;
> >> >> >> linux-fsdevel@...r.kernel.org
> >> >> >> Subject: Re: [PATCH 00/16] f2fs: introduce flash-friendly file
> >> >> >> system
> >> >> >>
> >> >> >> Il 06/10/2012 22:06, Jaegeuk Kim ha scritto:
> >> >> >>> 2012-10-06 (토), 17:54 +0400, Vyacheslav Dubeyko:
> >> >> >>>> Hi Jaegeuk,
> >> >> >>>
> >> >> >>> Hi.
> >> >> >>> We know each other, right? :)
> >> >> >>>
> >> >> >>>>
> >> >> >>>>> From:	 	김재극 <jaegeuk.kim@...sung.com>
> >> >> >>>>> To:	 	viro@...iv.linux.org.uk, 'Theodore Ts'o' <tytso@....edu>,
> >> >> >> gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
> >> >> >> chur.lee@...sung.com,
> >> >> cm224.lee@...sung.com,
> >> >> >> jaegeuk.kim@...sung.com, jooyoung.hwang@...sung.com
> >> >> >>>>> Subject:	 	[PATCH 00/16] f2fs: introduce flash-friendly file
> >> >> >>>>> system
> >> >> >>>>> Date:	 	Fri, 05 Oct 2012 20:55:07 +0900
> >> >> >>>>>
> >> >> >>>>> This is a new patch set for the f2fs file system.
> >> >> >>>>>
> >> >> >>>>> What is F2FS?
> >> >> >>>>> =============
> >> >> >>>>>
> >> >> >>>>> NAND flash memory-based storage devices, such as SSD, eMMC, and
> >> >> >>>>> SD
> >> >> >>>>> cards, have
> >> >> >>>>> been widely being used for ranging from mobile to server
> >> >> >>>>> systems.
> >> >> >>>>> Since they are
> >> >> >>>>> known to have different characteristics from the conventional
> >> >> >>>>> rotational disks,
> >> >> >>>>> a file system, an upper layer to the storage device, should adapt
> >> >> >>>>> to
> >> >> >>>>> the changes
> >> >> >>>>> from the sketch.
> >> >> >>>>>
> >> >> >>>>> F2FS is a new file system carefully designed for the NAND flash
> >> >> >>>>> memory-based storage
> >> >> >>>>> devices. We chose a log structure file system approach, but we
> >> >> >>>>> tried
> >> >> >>>>> to adapt it
> >> >> >>>>> to the new form of storage. Also we remedy some known issues of
> >> >> >>>>> the
> >> >> >>>>> very old log
> >> >> >>>>> structured file system, such as snowball effect of wandering
> >> >> >>>>> tree
> >> >> >>>>> and high cleaning
> >> >> >>>>> overhead.
> >> >> >>>>>
> >> >> >>>>> Because a NAND-based storage device shows different
> >> >> >>>>> characteristics
> >> >> >>>>> according to
> >> >> >>>>> its internal geometry or flash memory management scheme aka FTL,
> >> >> >>>>> we
> >> >> >>>>> add various
> >> >> >>>>> parameters not only for configuring on-disk layout, but also for
> >> >> >>>>> selecting allocation
> >> >> >>>>> and cleaning algorithms.
> >> >> >>>>>
> >> >> >>>>
> >> >> >>>> What about F2FS performance? Could you share benchmarking results
> >> >> >>>> of
> >> >> >>>> the new file system?
> >> >> >>>>
> >> >> >>>> It is very interesting the case of aged file system. How is GC's
> >> >> >>>> implementation efficient? Could
> >> >> >> you share benchmarking results for the very aged file system state?
> >> >> >>>>
> >> >> >>>
> >> >> >>> Although I have benchmark results, currently I'd like to see the
> >> >> >>> results
> >> >> >>> measured by community as a black-box. As you know, the results are
> >> >> >>> very
> >> >> >>> dependent on the workloads and parameters, so I think it would be
> >> >> >>> better
> >> >> >>> to see other results for a while.
> >> >> >>> Thanks,
> >> >> >>>
> >> >> >>
> >> >> >> 1) Actually it's a strange approach. If you have got any results
> >> >> >> you
> >> >> >> should share them with the community explaining how (the workload,
> >> >> >> hw
> >> >> >> and so on) your benchmark works and the specific condition. I
> >> >> >> really
> >> >> >> don't like the approach "I've got the results but I don't say
> >> >> >> anything,
> >> >> >> if you want a number, do it yourself".
> >> >> >
> >> >> > It's definitely right, and I meant *for a while*.
> >> >> > I just wanted to avoid arguing with how to age file system in this
> >> >> > time.
> >> >> > Before then, I share the primitive results as follows.
> >> >> >
> >> >> > 1. iozone in Panda board
> >> >> > - ARM A9
> >> >> > - DRAM : 1GB
> >> >> > - Kernel: Linux 3.3
> >> >> > - Partition: 12GB (64GB Samsung eMMC)
> >> >> > - Tested on 2GB file
> >> >> >
> >> >> >           seq. read, seq. write, rand. read, rand. write
> >> >> > - ext4:    30.753         17.066       5.06         4.15
> >> >> > - f2fs:    30.71          16.906       5.073       15.204
> >> >> >
> >> >> > 2. iozone in Galaxy Nexus
> >> >> > - DRAM : 1GB
> >> >> > - Android 4.0.4_r1.2
> >> >> > - Kernel omap 3.0.8
> >> >> > - Partition: /data, 12GB
> >> >> > - Tested on 2GB file
> >> >> >
> >> >> >           seq. read, seq. write, rand. read,  rand. write
> >> >> > - ext4:    29.88        12.83         11.43          0.56
> >> >> > - f2fs:    29.70        13.34         10.79         12.82
> >> >> >
> >> >>
> >> >>
> >> >> This is results for non-aged filesystem state. Am I correct?
> >> >>
> >> >
> >> > Yes, right.
> >> >
> >> >>
> >> >> > Due to the company secret, I expect to show other results after
> >> >> > presenting f2fs at korea linux forum.
> >> >> >
> >> >> >> 2) For a new filesystem you should send the patches to
> >> >> >> linux-fsdevel.
> >> >> >
> >> >> > Yes, that was totally my mistake.
> >> >> >
> >> >> >> 3) It's not clear the pros/cons of your filesystem, can you share
> >> >> >> with
> >> >> >> us the main differences with the current fs already in mainline? Or
> >> >> >> is
> >> >> >> it a company secret?
> >> >> >
> >> >> > After forum, I can share the slides, and I hope they will be useful
> >> >> > to
> >> >> > you.
> >> >> >
> >> >> > Instead, let me summarize at a glance compared with other file
> >> >> > systems.
> >> >> > Here are several log-structured file systems.
> >> >> > Note that, F2FS operates on top of block device with consideration
> >> >> > on
> >> >> > the FTL behavior.
> >> >> > So, JFFS2, YAFFS2, and UBIFS are out-of scope, since they are
> >> >> > designed
> >> >> > for raw NAND flash.
> >> >> > LogFS is initially designed for raw NAND flash, but expanded to
> >> >> > block
> >> >> > device.
> >> >> > But, I don't know whether it is stable or not.
> >> >> > NILFS2 is one of major log-structured file systems, which supports
> >> >> > multiple snap-shots.
> >> >> > IMO, that feature is quite promising and important to users, but it
> >> >> > may
> >> >> > degrade the performance.
> >> >> > There is a trade-off between functionalities and performance.
> >> >> > F2FS chose high performance without any further fancy
> >> >> > functionalities.
> >> >> >
> >> >>
> >> >> Performance is a good goal. But fault-tolerance is also very important
> >> >> point. Filesystems are used by
> >> >> users, so, it is very important to guarantee reliability of data
> >> >> keeping.
> >> >> Degradation of performance
> >> >> by means of snapshots is arguable point. Snapshots can solve the
> >> >> problem
> >> >> not only some unpredictable
> >> >> environmental issues but also user's erroneous behavior.
> >> >>
> >> >
> >> > Yes, I agree. I concerned the multiple snapshot feature.
> >> > Of course, fault-tolerance is very important, and file system should
> >> > support
> >> > it as you know as power-off-recovery.
> >> > f2fs supports the recovery mechanism by adopting checkpoint similar to
> >> > snapshot.
> >> > But, f2fs does not support multiple snapshots for user convenience.
> >> > I just focused on the performance, and absolutely, the multiple
> >> > snapshot
> >> > feature is also a good alternative approach.
> >> > That may be a trade-off.
> >> >
> >> >> As I understand, it is not possible to have a perfect performance in
> >> >> all
> >> >> possible workloads. Could you
> >> >> point out what workloads are the best way of F2FS using?
> >> >
> >> > Basically I think the following workloads will be good for F2FS.
> >> > - Many random writes : it's LFS nature
> >> > - Small writes with frequent fsync : f2fs is optimized to reduce the
> >> > fsync
> >> > overhead.
> >> >
> >> >>
> >> >> > Maybe or obviously it is possible to optimize ext4 or btrfs to flash
> >> >> > storages.
> >> >> > IMHO, however, they are originally designed for HDDs, so that it may
> >> >> > or
> >> >> > may not suffer from
> >> >> fundamental designs.
> >> >> > I don't know, but why not designing a new file system for flash
> >> >> > storages
> >> >> > as a counterpart?
> >> >> >
> >> >>
> >> >> Yes, it is possible. But F2FS is not flash oriented filesystem as
> >> >> JFFS2,
> >> >> YAFFS2, UBIFS but block-
> >> >> oriented filesystem. So, F2FS design is restricted by block-layer's
> >> >> opportunities in the using of
> >> >> flash storages' peculiarities. Could you point out key points of F2FS
> >> >> design that makes this design
> >> >> fundamentally unique?
> >> >
> >> > As you can see the f2fs kernel document patch, I think one of the most
> >> > important features is to align operating units between f2fs and ftl.
> >> > Specifically, f2fs has section and zone, which are cleaning unit and
> >> > basic
> >> > allocation unit respectively.
> >> > Through these configurable units in f2fs, I think f2fs is able to reduce
> >> > the
> >> > unnecessary operations done by FTL.
> >> > And, in order to avoid changing IO patterns by the block-layer, f2fs
> >> > merges
> >> > itself some bios likewise ext4.
> >> Hello.
> >> The internal of eMMC and SSD is the blackbox from user side.
> >> How does the normal user easily set operating units alignment(page
> >> size and physical block size ?) between f2fs and ftl in storage device
> >> ?
> >
> > I've known that some works have been tried to figure out the units by
> > profiling the storage, AKA reverse engineering.
> > In most cases, the simplest way is to measure the latencies of consecutive
> > writes and analyze their patterns.
> > As you mentioned, in practical, users will not want to do this, so maybe we
> > need a tool to profile them to optimize f2fs.
> > In the current state, I think profiling is an another issue, and mkfs.f2fs
> > had better include this work in the future.
> Well, Format tool evaluates optimal block size whenever formatting? As
> you know, The size of Flash Based storage device is increasing every
> year. It means format time can be too long on larger devices(e.g. one
> device, one parition).

Every file systems will suffer from the long format time in such a huge device.
And, I don't think the profiling time would not be scaled up, since it's unnecessary to scan whole device.
After getting the size, we just can stop it.

> > But, IMO, from the viewpoint of performance, default configuration is quite
> > enough now.
> At default(after cleanly format), Would you share performance
> difference between other log structured filesystems in comparison to
> f2fs instead of ext4 ?
> 

Actually, we've focused on ext4, so I have no results of other file systems measured on embedded systems.
I'll test sooner or later, and report them.
Thank you for valuable comments.

> Thanks.
> >
> > ps) f2fs doesn't care about the flash page size, but considers garbage
> > collection unit.
> >
> >>
> >> Thanks.
> >>
> >> >
> >> >>
> >> >> With the best regards,
> >> >> Vyacheslav Dubeyko.
> >> >>
> >> >>
> >> >> >>
> >> >> >> Marco
> >> >> >
> >> >> > ---
> >> >> > Jaegeuk Kim
> >> >> > Samsung
> >> >> >
> >> >> > --
> >> >> > To unsubscribe from this list: send the line "unsubscribe
> >> >> > linux-kernel"
> >> >> > in
> >> >> > the body of a message to majordomo@...r.kernel.org
> >> >> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >> >> > Please read the FAQ at  http://www.tux.org/lkml/
> >> >
> >> >
> >> > ---
> >> > Jaegeuk Kim
> >> > Samsung
> >> >
> >> > --
> >> > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel"
> >> > in
> >> > the body of a message to majordomo@...r.kernel.org
> >> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >> >
> >
> >
> > ---
> > Jaegeuk Kim
> > Samsung
> >
> >
> >


---
Jaegeuk Kim
Samsung

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