I'm working on a program running on Linux that uses mmap to map a number of files to memory.
Each of the files is read (walking the memory with pointers).
You clearly see in pmap how some files were completely mapped to memory (when read entirely) and others were not:
Address Kbytes RSS Dirty Mode Mapping
00007f8b09c3a000 26688 26664 0 rw-s- /mnt/ebs-metadata/fullyread.dat
00007f89ecc0c000 15936 4704 0 rw-s- /mnt/ebs-metadata/partiallyread.dat
We continue mapping files and at a certain point in time we get an error saying more memory can't be allocated.
(Yes, we can unload many files, and we will do).
My question is: why the OS doesn't unload many of the pages (or even full files) from physical memory until the next use instead of throwing "cannot allocate memory"?
