Filling RAM

Filling RAM

[DMcLeod]

Hi,

I am seeing that as files are created, their approximate size is 
subtracted from the available memory. For example, assume I have /home  
mounted from /dev/mtdblock2, which is a jffs2 filesystem on NOR flash. 
The following procedure reproduces the problem consistently:

[code]
]# cat /proc/mounts
rootfs        /     rootfs  rw     0 0
/proc        /proc     proc     rw     0 0
sysfs        /sys     sysfs     rw     0 0
/dev/mtdblock2    /home     jffs2     rw,sync 0 0

]# cd /home
]# grep MemFree /proc/meminfo
22588 kB
]# dd if=/dev/zero of=1M.dat bs=1M count=1
...
]# grep MemFree /proc/meminfo
21522 kB
]# rm 1M.dat
]# grep MemFree /proc/meminfo
22576 kB
[/code]

I'm fairly certain the file does get written to flash as it is 
noticeably slower than creating a file of the same size in ramfs. So it 
seems like the file is stored in RAM as well, how/why would this happen?

ps - XATTRS is off,  JFFS2_SUMMARY is off, JFFS2_VERBOSITY = 0,


Any help is greatly appreciated.

Re: Filling RAM

[Ricard Wanderlof]

On Tue, 5 Feb 2008, DMcLeod wrote:

> I am seeing that as files are created, their approximate size is
> subtracted from the available memory. For example, assume I have /home
> mounted from /dev/mtdblock2, which is a jffs2 filesystem on NOR flash.
> ...
> ]# cd /home
> ]# grep MemFree /proc/meminfo
> 22588 kB
> ...

MemFree in /proc/meminfo is not a good indicator of how much available 
memory there is to the system. Linux tends to gobble up memory for file 
buffers etc, freeing them on an as-needed basis. IIUC MemFree principally
indicates how much memory has never been touched, not how much is actually 
available.

/Ricard
--
Ricard Wolf Wanderlöf                           ricardw(at)axis.com
Axis Communications AB, Lund, Sweden            www.axis.com
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