On Wed, 25 Aug 2010 14:33:06 -0700 Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote: > >> 2 requires a deeper understanding of the existing hotplug code. It > >> needs to be refactored so that you can use the core hotplug machinery > >> without enabling the sysfs page-onlining mechanism, while still leaving > >> it available for physical hotplug. In the short term, having a boolean > >> to disable the onlining mechanism is probably the pragmatic solution, so > >> the balloon code can simply disable it. > > I think that sysfs should stay intact because it contains some > > useful information for admins. We should reconsider avaibilty > > of /sys/devices/system/memory/probe. In physical systems it > > is available however usage without real hotplug support > > lead to big crash. I am not sure we should disable probe in Xen. > > Maybe it is better to stay in sync with standard behavior. > > Second solution is to prepare an interface (kernel option > > or only some enable/disable functions) which give possibilty > > to enable/disable probe interface when it is required. > > My understanding is that on systems with real physical hotplug memory, > the process is: > > 1. you insert/enable a DIMM or whatever to make the memory > electrically active > 2. the kernel notices this and generates a udev event > 3. a usermode script sees this and, according to whatever policy it > wants to implement, choose to online the memory at some point > > I'm concerned that if we partially implement this but leave "online" as > a timebomb then existing installs with hotplug scripts in place may poke > at it - thinking they're dealing with physical hotplug - and cause problems. > IIUC, IBM guys, using LPAR?, does memory hotplug on VM. The operation is. 1. tell the region of memory to be added to a userland daemon. 2. The daemon write 0xXXXXXX > /sys/devices/system/memory/probe (This notifies that memory is added physically.) Here, memory is created. 3. Then, online memory. I think VM guys can use similar method rather than simulating phyiscal hotplug. Then, you don't have to worry about udev etc... No ? Thanks, -Kame -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>