On 9/28/07, linux-os (Dick Johnson) <[EMAIL PROTECTED]> wrote: > > On Fri, 28 Sep 2007, [iso-8859-1] Daniel Spång wrote: > > > On 9/28/07, linux-os (Dick Johnson) <[EMAIL PROTECTED]> wrote: > >> > >> On Fri, 28 Sep 2007, [iso-8859-1] Daniel Spång wrote: > >> > >>> On 9/28/07, linux-os (Dick Johnson) <[EMAIL PROTECTED]> wrote: > >>>> > >>>> But an embedded system contains all the software that will > >>>> ever be executed on that system! If it is properly designed, > >>>> it can never run out of memory because everything it will > >>>> ever do is known at design time. > >>> > >>> Not if its input is not known beforehand. Take a browser in a mobile > >>> phone as an example, it does not know at design time how big the web > >>> pages are. On the other hand we want to use as much memory as > >>> possible, for cache etc., a method that involves the kernel would > >>> simplify this and avoids setting manual limits. > >>> > >>> Daniel > >>> > >> > >> Any networked appliance can (will) throw data away if there are > >> no resources available. > >> > >> The length of a web-page is not relevent, nor is the length > >> of any external data. Your example will buffer whatever it > >> can and not read anything more from the external source until > >> it has resources available unless it is broken. > > > > And how do you determine when no resources are availabe? We are using > > overcommit here so malloc() will always return non null. > > > > A networked appliance using embedded software is not your daddy's > Chevrolet. Any task that is permanent needs to allocate all its > resources when it starts. That's how it knows how much there are, > and incidentally, it doesn't do it blindly. The system designer > must know how much memory is available in the system and how much > is allocated to the kernel. > > The fact that you can give a fictitious value to malloc() is not > relevant. If you don't provide resources for malloc(), like > (ultimately) a swap file, then you can't assume that it can do > any design work for you. > > An embedded system is NOT an ordinary system that happens to > boot from flash. An embedded system requires intelligent design.
We might be talking about slightly different systems. I agree that systems that are really embedded, in the classic meaning often with real time constraints, should be designed as you suggests. But there are a lot of other systems that almost actually are ordinary systems but with limited memory and often without demand paging. This could be a set top box, a video game console or a mobile phone that run dynamic applications. Actually this is not only about applications allocating an unknown amount of dynamic memory. A similar situation could also appear when we run an unknown number of applications at once, each allocating just a static amount of memory and then later starts to touching it. For those systems I think we need a method to dynamically decrease the working set of a process when memory is scarce, and not just accept that we "are screwed" and let the OOM killer solve the problem. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
