On Thu, 10 Mar 2011, Mordae wrote: > As I understand that, before a process forks, all of it's private memory > pages are somehow magically marked. When a process with access to such > page attempts to modify it, the page is duplicated and the copy replaces > the shared page for this process. Then the actual modification is > carried on. Its not magic. The kernel simply marks the pages as readonly and does a copy operation when the page is modified. > What I am interested in is a hypothetical system call > > void *mcopy(void *dst, void *src, size_t len, int flags); > > which would make src pages marked in the same way and mapped *also* to > the dst. Afterwards, any modification to either mapping would not > influence the other. > > Now, is there something like that? If you have a file backed mmap (could be tmpfs) then it is possible. First establish an RW mapping of the file. Then -- when you want to take the snapshot -- unmap it and do two mmaps to the old and new location. Make both readonly and MAP_PRIVATE. That will cause the kernel to create readonly pages that are subject to COW. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>