On 2014/7/25 1:59, Dave Hansen wrote: > On 07/24/2014 12:41 AM, Zhang Zhen wrote: >> Currently memory-hotplug has two limits: >> 1. If the memory block is in ZONE_NORMAL, you can change it to >> ZONE_MOVABLE, but this memory block must be adjacent to ZONE_MOVABLE. >> 2. If the memory block is in ZONE_MOVABLE, you can change it to >> ZONE_NORMAL, but this memory block must be adjacent to ZONE_NORMAL. >> >> Without this patch, we don't know which zone a memory block is in. >> So we don't know which memory block is adjacent to ZONE_MOVABLE or >> ZONE_NORMAL. >> >> On the other hand, with this patch, we can easy to know newly added >> memory is added as ZONE_NORMAL (for powerpc, ZONE_DMA, for x86_32, >> ZONE_HIGHMEM). > > A section can contain more than one zone. This interface will lie about > such sections, which is quite unfortunate. > 1. In arch_add_memory(), x86_64 add the new pages of the new memory block default to ZONE_NORMAL (for powerpc, ZONE_DMA, for x86_32, ZONE_HIGHMEM). 2. In __offline_pages(), test_pages_in_a_zone() guaranteed the pages of a memory block we try to offline are in the same zone. If a section contains more than one zone, the memory block can not be offlined. Based on the above two points, i think the pages of a memory block are in one zone, and the sections of a memory block are in one zone. Could you please explain in detail what is the case a section can contain more than one zone ? Thanks for your comments! > I'd really much rather see an interface that has a section itself > enumerate to which zones it may be changed. The way you have it now, > any user has to know the rules that you've laid out above. If the > kernel changed those restrictions, we'd have to teach every application > about the change in restrictions. > This interface is designed to show which zone a memory block is in. If the kernel changed those restrictions, this interface doesn't need to change. For a x86_64 machine booted with "mem=400M" and with 2GiB memory installed. Sample output of the sysfs files: # cat block_size_bytes 8000000 # cat memory0/zone_index DMA # cat memory1/zone_index DMA32 # cat memory2/zone_index DMA32 # cat memory3/zone_index DMA32 # echo 0x20000000 > probe # cat memory4/zone_index Normal # echo online > memory4/state # cat memory4/zone_index Normal # echo offline > memory4/state # echo online_movable > memory4/state # cat memory4/zone_index Movable Thanks! Best regards! > > > > . > -- 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>