On 2013/2/1 10:06, Simon Jeons wrote: > 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? Yes. > >> >>> >>>> >>>>> 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
