On 07.01.20 14:36, Michal Hocko wrote: > On Tue 07-01-20 21:09:42, lantianyu1986@xxxxxxxxx wrote: >> From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> >> >> Hyper-V balloon driver will use is_mem_section_removable() to >> check whether memory block is removable or not when receive >> memory hot remove msg. Expose it. > > I do not think this is a good idea. The check is inherently racy. Why > cannot the balloon driver simply hotremove the region when asked? > It's not only racy, it also gives no guarantees. False postives and false negatives are possible. If you want to avoid having to loop forever trying to offline when calling offline_and_remove_memory(), you could try to alloc_contig_range() the memory first and then play the PG_offline+notifier game like virtio-mem. I don't remember clearly, but I think pinned pages can make offlining loop for a long time. And I remember there were other scenarios as well (including out of memory conditions and similar). I sent an RFC [1] for powerpc/memtrace that does the same (just error handling is more complicated as it wants to offline and remove multiple consecutive memory blocks) - if you want to try to go down that path. [1] https://lkml.kernel.org/r/20191217123851.8854-1-david@xxxxxxxxxx -- Thanks, David / dhildenb
