dhb (03/25/83)
Has anyone ever investigated the possibility of having more than fifteen file systems mounted at one time? We are running 4.1 BSD on a VAX 11/780 with two RM05's and two RM03's. In the near fu- ture we plan to add three more RM05's and would like to be able to partition the file space into more than fifteen file systems. I tried changing the definition of "struct cmap" and the values of "NMOUNT" and "NSWAPX", and re-compiling the entire system but that didn't seem to work. If anyone can help me out on this I would greatly appreciate it. Dave Brierley ...!brunix!rayssd!dhb Please reply to net.unix-wizards as mail has a habit of never making it this far.
tjt (04/02/83)
The 4BSD paging algorithm keeps a table of information about each page in physical memory (except those allocated very early in the startup procedure). This structure (in <sys/cmap.h>) includes the field c_mdev:4 to identify which mounted file system a page came from, and is used for retaining text pages of pageable text files (magic number 0413) after the page has been released. I think it is also for identifying "reclaimable" pages. i.e. pages made inaccessable to a process but retained in memory. This is the mechanism used to simulate a "page referenced" bit. As a special added attraction, if c_mdev is equal to NMOUNT, the page came from the swap area (i.e. it's a data or stack page). In any case, if you make NMOUNT >= 16, you had better add more bits to the c_mdev field as well.