On 02/06/20 at 07:50am, Wei Yang wrote: > On Thu, Feb 06, 2020 at 07:19:45AM +0800, Wei Yang wrote: > >On Wed, Feb 05, 2020 at 02:52:51PM +0100, David Hildenbrand wrote: > >>Let's use a calculation that's easier to understand and calculates the > >>same result. Reusing existing macros makes this look nicer. > >> > >>We always want to have the number of pages (> 0) to the next section > >>boundary, starting from the current pfn. > >> > >>Suggested-by: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx> > >>Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > >>Cc: Michal Hocko <mhocko@xxxxxxxxxx> > >>Cc: Oscar Salvador <osalvador@xxxxxxx> > >>Cc: Baoquan He <bhe@xxxxxxxxxx> > >>Cc: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> > >>Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > > > >Reviewed-by: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> > > > >BTW, I got one question about hotplug size requirement. > > > >I thought the hotplug range should be section size aligned, while taking a > >look into current code function check_hotplug_memory_range() guard the range. A good question. The current code should be block size aligned. I remember in some places we assume each block comprise all the sections. Can't imagine one or some of them are half section filled. It truly has a risk that system ram is very huge to make the block size is 2G, someone try to insert a 1G memory board. However, it should only exist in experiment environment, e.g build a guest with enough ram, then hot add 1G DIMM. In reality, we don't need to worry about it, at least what I saw is 512G order of magnitude. > > > >This function says the range should be block_size aligned. And if I am > >correct, block size on x86 should be in the range > > > > [MIN_MEMORY_BLOCK_SIZE, MEM_SIZE_FOR_LARGE_BLOCK] > > > >And MIN_MEMORY_BLOCK_SIZE is section size. No, if I got it right, the range on x86 is [MIN_MEMORY_BLOCK_SIZE, MAX_BLOCK_SIZE]. MEM_SIZE_FOR_LARGE_BLOCK is the starting point from which block size can be adjusted. Otherwise it's MIN_MEMORY_BLOCK_SIZE. /* Amount of ram needed to start using large blocks */ #define MEM_SIZE_FOR_LARGE_BLOCK (64UL << 30) > > > >Seems currently we support subsection hotplug? Then how a subsection range got > >hotplug? Or this patch is a pre-requisite? The sub-section hotplug feature was added by your colleague Dan Williams. It intends to fix a nvdimms issue that nvdimms device could be mapped into a non section size aligned starting address. And nvdimms makes use of the existing memory hotplug mechanism to manage pages. Not sure if we are saying the same thing. > > > > One more question is we support hot-add subsection memory but not support > hot-online subsection memory. > > Is my understanding correct? > > -- > Wei Yang > Help you, Help me >
