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Subject: Re: Q: Cramfs Vs. Ubifs
From: Nathan Lynch <ntl@pobox.com>
To: Ran Shalit <ranshalit@gmail.com>
Date: Wed, 13 Jun 2012 10:46:20 -0500
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On Wed, 2012-06-13 at 18:25 +0300, Ran Shalit wrote:
> > Even if you copy all files to a RAM-based file system, such as /tmp, they
> > still need to be copied from the file system to directly accessible memory
> > before execution. While it may be faster than performing the same operation
> > from flash, the demand paging functionality is still in operation.
> >
> > The only way to avoid it would be to force loading of all pages for a
> > program at its start, I've never had the need so I don't know how though.
> >
> >
> Yes, that what I meant. At the initialization stage we will copy all
> files from ubifs section into root file system in RAM and so I assume
> that there will be no any access to flash during application life for
> read or write (any desired access will be controlled by application).
> I wonder why I didn't find any information about disadvantage of using
> ubifs as root file system in embedded system in terms of access to
> flash during application life.

This isn't an issue specific to UBIFS.  Look into mlock/mlockall if your
application needs to avoid latencies associated with demand-paging from
flash or any other storage.