A file of 5 MB on tmpfs file system uses 5 MB of RAM or more?

A file of 5 MB on tmpfs file system uses 5 MB of RAM or more?

[DI BACCO ANTONIO - technolabs]

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I have a linux-2.6.19.2 board with an MPC880 with 16MB ram and 16 MB
flash. 
Normally I have 9-10 MB of free RAM.
 
If I allocate 5 MB of ram memory, the system continues to work normally,
but if, instead of allocating 5 MB directly, I fill the /tmp directory
(that has a tmpfs file system) with a 5MB file the system becomes slow
and after some minutes the oom_killer is invoked. Before it dies I had
the time to see that mtdblockd is taking a lot of CPU (20%), what could
be the problem?
 
Any hint will be appreciate,
Bye,
Antonio.

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Re: A file of 5 MB on tmpfs file system uses 5 MB of RAM or more?

[Kumar Gala]

On Jan 18, 2008, at 7:15 AM, DI BACCO ANTONIO - technolabs wrote:

> I have a linux-2.6.19.2 board with an MPC880 with 16MB ram and 16 MB  
> flash.
> Normally I have 9-10 MB of free RAM.
>
> If I allocate 5 MB of ram memory, the system continues to work  
> normally, but if, instead of allocating 5 MB directly, I fill the / 
> tmp directory (that has a tmpfs file system) with a 5MB file the  
> system becomes slow and after some minutes the oom_killer is  
> invoked. Before it dies I had the time to see that mtdblockd is  
> taking a lot of CPU (20%), what could be the problem?
>
Posting any output from OOM, etc would be useful.

- k

Re: A file of 5 MB on tmpfs file system uses 5 MB of RAM or more?

[Scott Wood]

On Fri, Jan 18, 2008 at 02:15:02PM +0100, DI BACCO ANTONIO - technolabs wrote:
> I have a linux-2.6.19.2 board with an MPC880 with 16MB ram and 16 MB
> flash. 
> Normally I have 9-10 MB of free RAM.
>  
> If I allocate 5 MB of ram memory, the system continues to work normally,

Are you sure the RAM was actually allocated (i.e. did you write to all of
the pages)?

-Scott

RE: A file of 5 MB on tmpfs file system uses 5 MB of RAM or more?

[DI BACCO ANTONIO - technolabs]

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No I simply did several malloc(s) without writing to the allocated space.

This means that the pages are not allocated really?



-----Original Message-----
From: Scott Wood [mailto:scottwood@freescale.com]
Sent: Fri 18/01/2008 16.58
To: DI BACCO ANTONIO - technolabs
Cc: linuxppc-embedded@ozlabs.org
Subject: Re: A file of 5 MB on tmpfs file system uses 5 MB of RAM or more?
 
On Fri, Jan 18, 2008 at 02:15:02PM +0100, DI BACCO ANTONIO - technolabs wrote:
> I have a linux-2.6.19.2 board with an MPC880 with 16MB ram and 16 MB
> flash. 
> Normally I have 9-10 MB of free RAM.
>  
> If I allocate 5 MB of ram memory, the system continues to work normally,

Are you sure the RAM was actually allocated (i.e. did you write to all of
the pages)?

-Scott


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Re: A file of 5 MB on tmpfs file system uses 5 MB of RAM or more?

[Scott Wood]

DI BACCO ANTONIO - technolabs wrote:
> No I simply did several malloc(s) without writing to the allocated space.
> 
> This means that the pages are not allocated really?

Correct.

-Scott