Hi Jianguo, On Fri, 2013-02-01 at 09:57 +0800, Jianguo Wu wrote: > 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. IIUC, the benefit of va() and pa() is just for quick get virtual/physical address, it takes advantage of linear mapping. But mmu still need to go through pgd/pud/pmd/pte, correct? > > > > >> > >>> 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
