Well, you lose access to whatever is swapped. Which is why you may just be very screwed. If/when I invest in that 32 GB class 10 MicroSD card I am hoping to acquire eventually, I will be happy to test this unmount-during-swapping scenario. Too lazy to do it with my current somewhat-small-capacity, slower ones.

Also, the above test I mentioned above while downloading catalog 8/9 was with Laptop mode on. I turned laptop mode off for this next test (catalog 9/9, significantly bigger) - while leaving the massive dirty (background) ratio values... So that combination was a bit less than ideal. Download speed was nice, but UI responsiveness ground to a halt in some moments... Hmmm, specifically, during the actual finishing of the download. It had the same horrible unresponsiveness during the previous test for about a minute or so, when it finished downloading that catalog.

So what does that tell us? Laptop mode on-off doesn't seem to effect either sustained downloading or the finalizing of the write of that file, that I could notice. By itself, however, it seems that just lowering the I/O queues, but not changing the ratios or the vfs_cache_pressure, doesn't solve the unresponsiveness problem.

On the other hand, for all I know, it does, and had this been an N900 with all values at stock, the same slowness/UI-paralysis could have lasted much longer, when downloading that big of a file and saving it, all the while having Stellarium running in the background, with real time and a decently wide viewing angle, plus twinkle for the stars enabled.

So, to sumrise, when using Stellarium's built in catalogue download, tweakings JUST the queue sizes down seems to increase download speed, but, if your dirty ratio and dirty background ratio are high, swappiness is low, you do NOT have regular pdf flush daemon wakeups enables (mine don't wake up automatically, I have both centisecs values at 0), there is still a massive slow-down when finishing the download.

My GUESS is that had I had the centisecs values set to something low, or the ratio values set to something low, both would have lessened the final slow-down as well, probably significantly, because with dirty ratio at 95 and dirty background ratio at 65, and no routine flush daemons waking up, the dirty pages built up, both in RAM and in swap, I suspect.

Speaking of which, Stellarium runs great with all star cataloges downloaded. This is the non-mobile one. The mobile one presumably does even better.