Re: [PATCH 00/16] f2fs: introduce flash-friendly file system

From: Namjae Jeon <linkinjeon@gmail.com>
To: Jaegeuk Kim <jaegeuk.kim@gmail.com>
Cc: Jaegeuk Kim <jaegeuk.kim@samsung.com>,
	Arnd Bergmann <arnd@arndb.de>,
	David Woodhouse <dwmw2@infradead.org>,
	Luk Czerner <lczerner@redhat.com>,
	Vyacheslav Dubeyko <slava@dubeyko.com>,
	Marco Stornelli <marco.stornelli@gmail.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	tytso@mit.edu, gregkh@linuxfoundation.org,
	linux-kernel@vger.kernel.org, chur.lee@samsung.com,
	cm224.lee@samsung.com, jooyoung.hwang@samsung.com,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 00/16] f2fs: introduce flash-friendly file system
Date: Wed, 17 Oct 2012 20:12:38 +0900	[thread overview]
Message-ID: <CAKYAXd80822Gw1xfGwAqp99f+3VFgmpAH9FwwTmHU5xGbB-Puw@mail.gmail.com> (raw)
In-Reply-To: <1350131840.1917.53.camel@kjgkr>

2012/10/13, Jaegeuk Kim <jaegeuk.kim@gmail.com>:
> 2012-10-13 (토), 13:26 +0900, Namjae Jeon:
>> Is there high possibility that the storage device can be rapidly
>> worn-out by cleaning process ? e.g. severe fragmentation situation by
>> creating and removing small files.
>>
>
> Yes, the cleaning process in F2FS induces additional writes so that
> flash storage can be worn out quickly.
> However, how about in traditonal file systems?
> As all of us know that, FTL has an wear-leveling issue too due to the
> garbage collection overhead that is fundamentally similar to the
> cleaning overhead in LFS or F2FS.
>
> So, what's the difference between them?
> IMHO, the major factor to reduce the cleaning or garbage collection
> overhead is how to efficiently separate hot and cold data.
> So, which is a better layer between FTL and file system to achieve that?
> I think the answer is the file system, since the file system has much
> more information on such a hotness of all the data, but FTL doesn't know
> or is hard to figure out that kind of information.
>
> Therefore, I think the LFS approach is more beneficial to span the life
> time of the storage rather than traditional one.
> And, in order to do this perfectly, one thing is a criteria, the
> alignment between FTL and F2FS.

As you know, Normally users don't use one big partition on eMMC.
It means they divide several small parititions.
And F2fs will work on each small partition.
And eMMC's FTL is globally working on whole device.
I can not imagine how to work synchronously beween cleaning process of
f2fs and FTL of eMMC.

And Would you share ppt or document of f2fs if Korea Linux Forum is finished ?

Thanks.
>
>> And you told us only advantages of f2fs. Would you tell us the
>> disadvantages ?
>
> I think there is a scenario like this.
> 1) One big file is created and written data sequentially.
> 2) Many random writes are done across the whole file range.
> 3) User discards cached data by doing "drop_caches" or "reboot".
>
> At this point, I worry about the sequential read performance due to the
> fragmentation.
> I don't know how frequently this use-case happens, but it is one of cons
> in the LFS approach.
> Nevertheless, I'm thinking that the performance could be enhanced by
> cooperating with a readahead mechanism in VFS.
>
> Thanks,
>
>>
>> Thanks.
>
> --
> Jaegeuk Kim
> Samsung
>
>