[Fwd: Re: a problem about jffs2]

[Fwd: Re: a problem about jffs2]

[Artem B. Bityutskiy]

Just forwarding to the appropriate mailing list.

		Artem.

-------- Original Message --------
Subject: Re: a problem about jffs2
Date: Wed, 9 Nov 2005 20:02:02 -0800 (PST)
From: Linus Torvalds <torvalds@osdl.org>
To: Thomas Gleixner <tglx@linutronix.de>,	David Woodhouse 
<dwmw2@infradead.org>,	"Artem B. Bityutskiy" <dedekind@infradead.org>, 
Todd Poynor <tpoynor@mvista.com>,	Ferenc Havasi <havasi@inf.u-szeged.hu>
References: <BAY114-F29E1CCEFBD64791D2C1DC28D660@phx.gbl>


Just forwarding to people who are more appropriate.

		Linus
--
YangLu YangLu <luyang_ly@hotmail.com>
On Thu, 10 Nov 2005, YangLu YangLu wrote:
>
> Dear Linus:
> 
> 	I recently meet a problem about jffs2.
> 
> 	There have three sectors in my mobilephone(OMAP730):
> 	/dev/mtdblock3           16384      3276     13108  20% /System
> 	/dev/mtdblock4            2048       388      1660  19% /Sysdisk
> 	/dev/mtdblock5            5120       388      4732   8% /Appdisk
> 
> 	I built new file(ph_bk) in /Sysdisk dirctory. 	I write a test
> program, as follows:
> 	1) open it.
> 	fd = fopen(argv[1], "r+");
> 	2) fseek with a random number, then write a number
> 	for (;;) {
> 		offset = rand();
> 		fseek(fd, offset % (1024*1024), SEEK_SET);
> 		fwrite(&offset,sizeof(int), 1, fd);
> 	}
> 
> 	I want to limit the file with 1M size, but when the test program run
> in background,
> 	this file maintain 1M size, but available space on /dev/mtdblock4
> continue to reduce, as below:
> 	Filesystem           1k-blocks      Used Available Use% Mounted on
> 	/dev/mtdblock4            2048       512      1536  25% /Sysdisk
> /dev/mtdblock4            2048       688      1360  34% /Sysdisk
> 	/dev/mtdblock4            2048       792      1256  39% /Sysdisk
> 	/dev/mtdblock4            2048       856      1192  42% /Sysdisk
> 	/dev/mtdblock4            2048      1212       836  59% /Sysdisk
> 	/dev/mtdblock4            2048      1516       532  74% /Sysdisk
> 	/dev/mtdblock4            2048      1920       128  94% /Sysdisk
> 
> 	Is it jffs2 filesystem's bug?
> 
> 	Thanks!
> 
> Best Regards,
> Richard
> 

Re: [Fwd: Re: a problem about jffs2]

[zhao, forrest]

> > Dear Linus:
> > 
> > 	I recently meet a problem about jffs2.
> > 
> > 	There have three sectors in my mobilephone(OMAP730):
> > 	/dev/mtdblock3           16384      3276     13108  20% /System
> > 	/dev/mtdblock4            2048       388      1660  19% /Sysdisk
> > 	/dev/mtdblock5            5120       388      4732   8% /Appdisk
> > 
> > 	I built new file(ph_bk) in /Sysdisk dirctory. 	I write a test
> > program, as follows:
> > 	1) open it.
> > 	fd = fopen(argv[1], "r+");
> > 	2) fseek with a random number, then write a number
> > 	for (;;) {
> > 		offset = rand();
> > 		fseek(fd, offset % (1024*1024), SEEK_SET);
> > 		fwrite(&offset,sizeof(int), 1, fd);
> > 	}
> > 
> > 	I want to limit the file with 1M size, but when the test program run
> > in background,
> > 	this file maintain 1M size, but available space on /dev/mtdblock4
> > continue to reduce, as below:
> > 	Filesystem           1k-blocks      Used Available Use% Mounted on
> > 	/dev/mtdblock4            2048       512      1536  25% /Sysdisk
> > /dev/mtdblock4            2048       688      1360  34% /Sysdisk
> > 	/dev/mtdblock4            2048       792      1256  39% /Sysdisk
> > 	/dev/mtdblock4            2048       856      1192  42% /Sysdisk
> > 	/dev/mtdblock4            2048      1212       836  59% /Sysdisk
> > 	/dev/mtdblock4            2048      1516       532  74% /Sysdisk
> > 	/dev/mtdblock4            2048      1920       128  94% /Sysdisk
> > 
> > 	Is it jffs2 filesystem's bug?
> > 
I once did some testing like yours, and had the same result.

I would say that this is an intrinsic nature of JFFS2 instead of a
JFFS2's bug.
Updating 4 bytes of a file for every write operation will cause
flash space wasting since every write operation generate an 
jffs2_raw_inode + 4 bytes on flash. sizeof(jffs2_raw_inode) is 68 bytes.

Thanks,
Forrest

Re: [Fwd: Re: a problem about jffs2]

[YangLu YangLu]

	But in linux-2.4.18(Now in linux-2.6.12) with same flash(NOR), 

	I used the same test routine, available space on /dev/mtdblock4 

	would not continue to reduce.

	Had GC's method been changed?

	Thanks!



Regards,
Richard


>From: "zhao, forrest" <forrest.zhao@intel.com>
>To: "Artem B. Bityutskiy" <dedekind@yandex.ru>
>CC: linux-mtd@lists.infradead.org, luyang_ly@hotmail.com
>Subject: Re: [Fwd: Re: a problem about jffs2]
>Date: Fri, 11 Nov 2005 11:32:27 +0800
>
>
> > > Dear Linus:
> > >
> > > 	I recently meet a problem about jffs2.
> > >
> > > 	There have three sectors in my mobilephone(OMAP730):
> > > 	/dev/mtdblock3           16384      3276     13108  20% /System
> > > 	/dev/mtdblock4            2048       388      1660  19% /Sysdisk
> > > 	/dev/mtdblock5            5120       388      4732   8% /Appdisk
> > >
> > > 	I built new file(ph_bk) in /Sysdisk dirctory. 	I write a test
> > > program, as follows:
> > > 	1) open it.
> > > 	fd = fopen(argv[1], "r+");
> > > 	2) fseek with a random number, then write a number
> > > 	for (;;) {
> > > 		offset = rand();
> > > 		fseek(fd, offset % (1024*1024), SEEK_SET);
> > > 		fwrite(&offset,sizeof(int), 1, fd);
> > > 	}
> > >
> > > 	I want to limit the file with 1M size, but when the test program run
> > > in background,
> > > 	this file maintain 1M size, but available space on /dev/mtdblock4
> > > continue to reduce, as below:
> > > 	Filesystem           1k-blocks      Used Available Use% Mounted on
> > > 	/dev/mtdblock4            2048       512      1536  25% /Sysdisk
> > > /dev/mtdblock4            2048       688      1360  34% /Sysdisk
> > > 	/dev/mtdblock4            2048       792      1256  39% /Sysdisk
> > > 	/dev/mtdblock4            2048       856      1192  42% /Sysdisk
> > > 	/dev/mtdblock4            2048      1212       836  59% /Sysdisk
> > > 	/dev/mtdblock4            2048      1516       532  74% /Sysdisk
> > > 	/dev/mtdblock4            2048      1920       128  94% /Sysdisk
> > >
> > > 	Is it jffs2 filesystem's bug?
> > >
>I once did some testing like yours, and had the same result.
>
>I would say that this is an intrinsic nature of JFFS2 instead of a
>JFFS2's bug.
>Updating 4 bytes of a file for every write operation will cause
>flash space wasting since every write operation generate an
>jffs2_raw_inode + 4 bytes on flash. sizeof(jffs2_raw_inode) is 68 bytes.
>
>Thanks,
>Forrest
>