[Android Software/Hacking General [Developers Only]] rancur3p1c:
I have 256MB ram :)

At the moment, Compcache is good enough, but I can't help but wonder how much better it could be with swap instead of Compcache.

edit: "For example, If you have a 256MB system (shows as 262MB due to 1024 vs. 1000 KB size difference) and have 130MB of apps and data/cache loaded, then that leaves about 130MB for the system to actually RUN programs. That sounds like a lot, but in reality that is not enough, since the system itself takes 50-80MB, and services will take up another 30-50MB, leaving almost nothing. "

quick review, you don't appear to be differentiating between RAM and Flash? Having more apps installed shouldn't increase RAM usage at all. Unless I gravely misunderstand the Android OS, if I install a new program, it resides in the system flash, not the RAM, until I run it, at which point it gets loaded to RAM. When the system needs memory and no swap or Compcache is in use, it writes the state of the application to the flash and removes it from RAM.

What the swap does is similar to what compcache does-- compresses apps that are currently in RAM, and moves them to the swap space. In the case of Compcache, this is in the RAM. But since you're compressing it, background apps don't take nearly as much RAM, and you get an app switching speedboost because the processor can uncompress the compcache'd program, "move" it to RAM, compress the currently running program in RAM, and "move" it to the compcache. Forgive me if you already said this, I can't read the entire thing at the moment.

As for swap, I'm not sure if the processor compresses before going to the hard swap file, I don't think that it does-- when android starts getting low on RAM, it moves what was in RAM, to the swap on the SD-card. Since it does this when the system is low on RAM, and not when the system runs out of RAM, you never notice it. Reading the app back from the SD card happens almost instantaneously, because the sd cards can be read from at a speed of at least 20MB/s, maybe more. When you're restoring an app to RAM, 20MB/s is plenty.

edit2: I'm sorry but this guide is too vague to be anything more than moderately informative. Comments like:

-"CompCache, or "compressed cache", is handled by the Linux kernel. It takes a portion of your memory, and use it as a cache space, but compressed. By using on-the-fly compression it is able to make your memory appear to be a bit larger than it actually is. However, the result is slower performance.

This is usually NOT tweakble without mod ROM such as Cyanogen Mod. The kernel also must support this feature, and not all do. This also slows your phone. "

-"...swap space by either creating a swap file or a swap partition. This adds a lot of read/write action to your SD card and may substantially decrease its usable life."

-"This really slows your phone."

People wouldn't be doing these things for no reason. Compcache does not "make your memory appear a bit larger", when it at least doubles the amount of usable RAM-- when you allocate 60MB, if you average 75% compression (I usually see between 65% and 80%), do you know how much RAM this effectively nets you? Over at least 60MB extra, usually about 80! So my phone goes from having 256MB ram to having 340 effectively. Having your processor overclocked minimizes any slowdown from the compression/decompression; I haven't noticed any slowdown, and having the "extra" RAM definitely has made my phone more able to multitask.

You basically discourage users from doing ANYTHING like swapping, compcaching, etc to their phone, saying it "slows it down" and "can substantially decrease your SD Card's life". My experience has been otherwise regarding slowing it down, and regarding the SD card, the only part that would actually go bad is the swap partition. If you put that at the end of the drive, when it goes bad, you'll know, and you can just move the partition back 300MB and put your 300MB swap there. We haven't heard of any users' cards going bad from this yet. Also, if you have a class 6+ SD Card, they implement wear leveling on the card, so you don't need to worry about wearing out any individual bits.

Sorry, I'm just not digging it.