On Tue, 26 Jan 2016, Felix von Leitner wrote: > > 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. You might find madvise(addr, length, MADV_DONTFORK) helpful: that tells fork not to duplicate the given range in the child. Hugh > > > Thanks, > > > Felix > > > PS: Please put me on Cc if you reply, I'm not subscribed to this mailing > > list. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>