Numa
It was some 15 years ago when I first heard about non uniform memory access. I spent the last 15 years not worrying about NUMA. Never checked, never worried, never cared.
So today I run some commands on some servers of mine to see what's going on. I wouldn't say I worry now, but there is certainly a new thing to think about.
So the first screenshot was made on a server that has 8 processors with memory integrated on all the processor cards. All the memory banks are populated. The stats are pretty straightforward, everything seems to be ok. Sun Microsystems, I like it...
The second has four processor slots, but only two of those populated and four, fully populated memory expansion cards. Well, it is showing only one memory area, right? I am not sure why... maybe the HW is built like that or the kernel doesn't handle it properly?
The third shows four processors, two populated memory expansion boards with RAM in them. There are also two unpopulated memory expansion boards. So it shows everything OK, but I know I should buy more RAM, right? The owner's manual also says it is better to have memory for every processor. Well, I bought some already (that's why there are two NUMA arrays already), the rest is on the way between China and the EU.
Oh, my, I hope when the ship arrives there will be two extra columns on this screen...