>> Nothing happens, because it _doesn't have to be resident_. >> > > Hm, but why in my case top show RSS 10g, when max HEAP_SIZE is 6G?
The point is that it is a result of how the kernel manages memory and how it is reported in top. It is not reflective of actual memory "use", the way users normally use the term. If you take a file that is 1 gig in file and "cat" it, it will end up in page cache. But that does not get accounted to any particular process. If on the other hand you mmap() the file in a process and stream through it, it will be accounted as part of the resident set of the process. But it is not indicative that the process is "using" that memory in the usual sense of the word. Since this keeps coming up I decided to put up the little test I have that can be used to demonstrate the effect: https://github.com/scode/alloctest You can run that and observe the effects in top. That said, there's *something* fishy going on in that whether pages get counted towards the process may be depending on something else. E.g., I have a node with ~ 1 TB virtual/sstable sizes that is actively doing AES (so should be doing mmap():ed i/o), yet I have exactly 10 gig (max heap size) RSS instead of > 10 gb. I haven't investigated properly. Maybe just depending on mmap flags. -- / Peter Schuller
