On 10.12.19 16:46, lantianyu1986@xxxxxxxxx wrote: > From: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> > > Hyper-V driver adds memory hot remove function and will use > these interfaces in Hyper-V balloon driver which may be built > as a module. Expose these function. This patches misses a detailed description how these interfaces will be used. Also, you should CC people on the actual magic where it will be used. I found it via https://lkml.org/lkml/2019/12/10/767 If I am not wrong (un)lock_device_hotplug() is not exposed to kernel modules for a good reason - your patch seems to ignore that if I am not wrong. > > Signed-off-by: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx> > --- > mm/memory_hotplug.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 07e5c67f48a8..4b358ebcc3d7 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1191,6 +1191,7 @@ bool is_mem_section_removable(unsigned long start_pfn, unsigned long nr_pages) > /* All pageblocks in the memory block are likely to be hot-removable */ > return true; > } > +EXPORT_SYMBOL_GPL(is_mem_section_removable); > > /* > * Confirm all pages in a range [start, end) belong to the same zone. > @@ -1612,6 +1613,7 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages) > { > return __offline_pages(start_pfn, start_pfn + nr_pages); > } > +EXPORT_SYMBOL_GPL(offline_pages); > > static int check_memblock_offlined_cb(struct memory_block *mem, void *arg) > { > No, I don't think exposing the latter is desired. We already have one other in-tree user that I _really_ want to get rid of. Memory should be offlined in memory block granularity via the core only. Memory offlining can be triggered in a clean way via device_offline(&mem->dev). a) It conflicts with activity from user space. Especially, this "manual fixup" of the memory block state is just nasty. b) Locking issues: Memory offlining requires the device hotplug lock. This lock is not exposed and we don't want to expose it. c) There are still cases where offline_pages() will loop for all eternity and only signals can kick it out. E.g., have a look at how I with virtio-mem want to achieve that: https://lkml.org/lkml/2019/9/19/476 I think something like that would be *much* cleaner. What could be even better for your use case is doing it similarly to virtio-mem: 1. Try to alloc_contig_range() the memory block you want to remove. This will not loop forever but fail in a nice way early. See https://lkml.org/lkml/2019/9/19/467 2. Allow to offline that memory block by marking the memory PageOffline() and dropping the refcount. See https://lkml.org/lkml/2019/9/19/470, I will send a new RFC v4 soon that includes the suggestion from Michal. 3. Offline+remove the memory block using a clean interface. See https://lkml.org/lkml/2019/9/19/476 No looping forever, no races with user space, no messing with memory block states. NACK on exporting offline_pages(), but I am not a Maintainer, so ... :) -- Thanks, David / dhildenb
