> Dear Linux kernel devs, > I talked to someone who uses large Linux based hardware to run a > process with huge memory requirements (think 4 GB), and he told me that > if they do a fork() syscall on that process, the whole system comes to > standstill. And not just for a second or two. He said they measured a 45 > minute (!) delay before the system became responsive again.
I'm sorry, I meant 4 TB not 4 GB. I'm not used to working with that kind of memory sizes. > Their working theory is that all the pages need to be marked copy-on-write > in both processes, and if you touch one page, a copy needs to be made, > and than just takes a while if you have a billion pages. > I was wondering if there is any advice for such situations from the > memory management people on this list. > In this case the fork was for an execve afterwards, but I was going to > recommend fork to them for something else that can not be tricked around > with vfork. > Can anyone comment on whether the 45 minute number sounds like it could > be real? When I heard it, I was flabberghasted. But the other person > swore it was real. Can a fork cause this much of a delay? Is there a way > to work around it? > I was going to recommend the fork to create a boundary between the > processes, so that you can recover from memory corruption in one > process. In fact, after the fork I would want to munmap almost all of > the shared pages anyway, but there is no way to tell fork that. > Thanks, > Felix > PS: Please put me on Cc if you reply, I'm not subscribed to this mailing > list.
