I think, among other things, it has to do with the size of the swap space relative to the speed of the swap device. IME high disk i/o combined with large swap space means swap never fills up and the OOM killer doesn't kick in. On systems with less RAM and swap, OOM conditions were hit much sooner, even with slower disks.

Default settings for dirty ratio and dirty background ratio exacerbate the issue: more data is held onto before it is written, and once the background ratio is hit, any application writing to disk will block.

With SSD's disk is not that slow.

SSDs are only ~4x faster than magnetic last I checked. If RAM is 100ns per access, and hd access is down from say, 1ms to 0.25ms, that's still a huge huge gap. 4x isn't even an order of magnitude.

EDIT: see comment below for more accurate numbers.

From the article:

>A typical reference to RAM is in the area of 100ns, accessing data on a SSD 150μs (so 1500 times of the RAM) and accessing data on a rotating disk 10ms (so 100.000 times the RAM.

reminded me of this...

Latency Numbers Every Programmer Should Know

https://gist.github.com/jboner/2841832

Thank you for the correction. I should have read more carefully. Still, we're talking 3 orders of magnitude for SSD vs RAM.