Date:	Tue, 9 Oct 2012 12:52:09 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	Jaegeuk Kim <jaegeuk.kim@...sung.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

2012/10/8, Jaegeuk Kim <jaegeuk.kim@...sung.com>:
>> -----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.
The key point is that you should estimate correct optimal block size
of ftl with much less I/O at format time.
I am not sure it is possible.
And you should prove optimal block size is really correct on several
device per vendor device.

>
>> > 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.
Okay, Thanks Jaegeuk.

> 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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