Hi Tang, On Thu, 2013-01-31 at 17:44 +0800, Tang Chen wrote: > Hi Simon, > > On 01/31/2013 04:48 PM, Simon Jeons wrote: > > Hi Tang, > > On Thu, 2013-01-31 at 15:10 +0800, Tang Chen wrote: > > > > 1. IIUC, there is a button on machine which supports hot-remove memory, > > then what's the difference between press button and echo to /sys? > > No important difference, I think. Since I don't have the machine you are > saying, I cannot surely answer you. :) > AFAIK, pressing the button means trigger the hotplug from hardware, sysfs > is just another entrance. At last, they will run into the same code. > > > 2. Since kernel memory is linear mapping(I mean direct mapping part), > > why can't put kernel direct mapping memory into one memory device, and > > other memory into the other devices? > > We cannot do that because in that way, we will lose NUMA performance. > > If you know NUMA, you will understand the following example: > > node0: node1: > cpu0~cpu15 cpu16~cpu31 > memory0~memory511 memory512~memory1023 > > cpu16~cpu31 access memory16~memory1023 much faster than memory0~memory511. > If we set direct mapping area in node0, and movable area in node1, then > the kernel code running on cpu16~cpu31 will have to access > memory0~memory511. > This is a terrible performance down. So if config NUMA, kernel memory will not be linear mapping anymore? For example, Node 0 Node 1 0 ~ 10G 11G~14G kernel memory only at Node 0? Can part of kernel memory also at Node 1? How big is kernel direct mapping memory in x86_64? Is there max limit? It seems that only around 896MB on x86_32. > > >As you know x86_64 don't need > > highmem, IIUC, all kernel memory will linear mapping in this case. Is my > > idea available? If is correct, x86_32 can't implement in the same way > > since highmem(kmap/kmap_atomic/vmalloc) can map any address, so it's > > hard to focus kernel memory on single memory device. > > Sorry, I'm not quite familiar with x86_32 box. > > > 3. In current implementation, if memory hotplug just need memory > > subsystem and ACPI codes support? Or also needs firmware take part in? > > Hope you can explain in details, thanks in advance. :) > > We need firmware take part in, such as SRAT in ACPI BIOS, or the firmware > based memory migration mentioned by Liu Jiang. Is there any material about firmware based memory migration? > > So far, I only know this. :) > > > 4. What's the status of memory hotplug? Apart from can't remove kernel > > memory, other things are fully implementation? > > I think the main job is done for now. And there are still bugs to fix. > And this functionality is not stable. > > Thanks. :) -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
