Re: Linux processes, tempfs and programs

[Eugene Surovegin <ebs@ebshome.net>]

On Thu, Feb 17, 2005 at 04:43:27PM -0800, Eugene Surovegin wrote:
> On Thu, Feb 17, 2005 at 03:38:05PM -0800, Stephen Williams wrote:
> > My embedded system is structured such that the main user-mode
> > processes that are being run are downloaded and executed on demand.
> > I'm currently downloading the executable to an ext3 system on the
> > CompactFlash, but there is really no reason to use non-volatile
> > memory so I'm thinking to download to a tempfs directory and
> > execute from there.
> > 
> > But if I do that, I want to remove the program from the directory
> > after I start it, so that the file does not take up ram space. Will
> > that actually work? I'm using exec(2) to execute the program file
> > wherever it is downloaded. Will a subsequent unlink of the file
> > have a result, or will the file continue to take up space as
> > backing store for the executable?
> 
> I think unlink will remove the file from directory (so you won't be
> able to see it with ls), but it will still continue to to take space -  
> you're right it will be used as backing store, at least for read-only 
> segments, which can be discarded if memory is tight. Even if you mlock 
> all executable in memory, I think there will be still at least one 
> reference to this file, which will prevent freeing tmpfs memory.

A little correction, according to tmpfs doc, it lives completely in 
page cache, so I think memory is not wasted for unmodified sections of 
the loaded file (e.g. a second copy, when file is executed and loaded 
into user-space, isn't being made).

But as usual, make some measurements first :)

--
Eugene.