Re: [9fans] plan 9 overcommits memory?

[geoff]

If system calls were the only way to change memory allocation, one
could probably keep a strict accounting of pages allocated and fail
system calls that require more VM than is available.  But neither Plan
9 nor Unix works that way.  The big exception is stack growth.  The
kernel automatically extends a process's stack segment as needed.  On
the pc, Plan 9 currently limits user-mode stacks to 16MB.  On a CPU
server with 200 processes (fairly typical), that's 3.2GB of VM one
would have to commit just for stacks.  With 2,000 processes, that
would rise to 32GB just for stacks.