On Thu, Feb 06, 2020 at 10:01:21AM +0100, David Hildenbrand wrote: >On 06.02.20 05:39, Baoquan He wrote: >> On 02/06/20 at 04:34am, Wei Yang wrote: >>> On Thu, Feb 06, 2020 at 10:48:16AM +0800, Baoquan He wrote: >>>> On 02/06/20 at 02:26am, Wei Yang wrote: >>>>> On Thu, Feb 06, 2020 at 08:37:36AM +0800, Baoquan He wrote: >>>>>> On 02/06/20 at 08:13am, Baoquan He wrote: >>>>>>> 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. >>>>>> >>>>>> I could be wrong, half filled block may not cause problem. >>>>>> >>>>> >>>>> David must be angry about our flooding the mail list :-) >>>> >>>> Believe he won't, :-) If you like, we can talk off line. >>>> >>>>> >>>>> Check the code again, there are two memory range check: >>>>> >>>>> * check_hotplug_memory_range(), block/section aligned >>>>> * check_pfn_span(), subsection aligned >>>>> >>>>> The second check, check_pfn_span() in __add_pages(), enable the capability to >>>>> add a memory range with subsection size. >>>>> >>>>> This means hotplug still keeps section alignment. >>>> >>>> memremap_pages() also call add_pages(), it doesn't have the >>>> check_hotplug_memory_range() invocation. check_pfn_span() is made for >>>> it specifically. >>>> >>> >>> If my understanding is correct, memremap_pages() is used to add some dev >>> memory to system. This is the use case which Dan want to enable for >>> sub-section. Since memremap_pages() is not called in mem-hotplug path, this >>> doesn't affect the hotplug range alignment. >> >> Yeah, we are on the same page. > >We allow sub-section hoy-add only for device memory/hmm. BIOS often >align PMEM devices to sub-sections, and not supporting this makes life >difficult to support these devices. (You cannot simply cut off something >of a disk :) ) > >System memory can only be hotplugged in memory block granularity, the >same granularity onlining/offlining from user space will happen. Boot >memory, however, can be sub-section aligned, but can never be offlined >(as it contains holes) and therefore never be removed. > This makes life easier. Thanks for your explanation. -- Wei Yang Help you, Help me
