On 2013/2/1 9:36, Simon Jeons wrote: > On Fri, 2013-02-01 at 09:32 +0800, Jianguo Wu wrote: >> On 2013/1/31 18:38, Simon Jeons wrote: >> >>> 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? >> >> >> Max kernel direct mapping memory in x86_64 is 64TB. > > For example, I have 8G memory, all of them will be direct mapping for > kernel? then userspace memory allocated from where? Direct mapping memory means you can use __va() and pa(), but not means that them can be only used by kernel, them can be used by user-space too, as long as them are free. > >> >>> 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, 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> >>> >>> . >>> >> >> >> > > > > . > -- 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
