Originally Posted by
ohliuw
There are loadfull of memory techniques. For example, ESXi uses something called Transient Page Sharing, which in other words is memory dedup.
Very similar to KSM ("Kernel Samepage merging") on Linux, normally used with KVM.
It also uses memory compression (caching of pages to be swapped), which outperforms swapping since decompressing is faster than loading from storage. However, the swap file is still, and no matter what memory management techniques you use, the swap is the last resort and is meant to be stored AWAY from the memory.
The difference is in how the techniques are implemented; zram appears to the OS as a block device, and uses the underlying swap-drive mechanism. In a logical sense, swap can refer to anything that takes memory out of the directly-addressable space and requires the OS to do work to access, whether it's on disk, elsewhere in RAM, or hypothetically out on the network somewhere. The code is closely tied to (for example) demand-paging from a memory-mapped file or executable.
I've written some of this stuff professionally. Have you?
Originally Posted by
ohliuw
Btw, there are many OSes that better than Linux, you know that, right
Heh, I'm not so sure about that these days. "Better" can be looked at overall, or for any specific job/set of criteria, of course, and for any specific job, there may be better options(*), but you will not find any other OS scale to as many different jobs as well overall -- or as cost effectively, for most of them.
In the overall sense of "better," I don't see one, and across all the platforms it's running no other OS is getting anywhere near the amount of testing or engineering effort that Linux is, so I expect that gap to keep growing.
(* a single instance of z/OS will be more reliable and scale to bigger hardware; the GUIs in Windows and the MacOS are more mature; Solaris and the free *BSDs have some
specific ways in which they're more efficient. I can't think of a single nice thing to say about AIX though
)