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. > 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
