On 04/09/2013 02:30 AM, Andrew Morton wrote: > On Fri, 05 Apr 2013 21:06:12 +0400 Pavel Emelyanov <xemul@xxxxxxxxxxxxx> wrote: > >> Hello, >> >> This is another attempt (previous one was [1]) to implement support for >> memory snapshot for the the checkpoint-restore project (http://criu.org). >> Let me remind what the issue is. >> >> << EOF >> To create a dump of an application(s) we save all the information about it >> to files, and the biggest part of such dump is the contents of tasks' memory. >> However, there are usage scenarios where it's not required to get _all_ the >> task memory while creating a dump. For example, when doing periodical dumps, >> it's only required to take full memory dump only at the first step and then >> take incremental changes of memory. Another example is live migration. We >> copy all the memory to the destination node without stopping all tasks, then >> stop them, check for what pages has changed, dump it and the rest of the state, >> then copy it to the destination node. This decreases freeze time significantly. >> >> That said, some help from kernel to watch how processes modify the contents >> of their memory is required. Previous attempt used ftrace to inform userspace >> about memory being written to. This one is different. >> >> EOF > > Did you consider teaching the kernel to perform a strong hash on a > page's contents so that userspace can do a before-and-after check to see > if it changed? I did (unless I misunderstood _your_ idea with hashes :( ), but judged, that a single bit on a pte would be less cpu and memory consuming than calculating and keeping 32/64 bits of hash value. As far as all other comments are concerned -- thanks a LOT for the feedback! I will address them all. Thanks, Pavel -- 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>