On Mon, Oct 15, 2018 at 8:31 AM Oscar Salvador <osalvador@xxxxxxxxxxxxxxxxxx> wrote: > > From: Oscar Salvador <osalvador@xxxxxxx> > > HMM/devm have a particular handling of memory-hotplug. > They do not go through the common path, and so, they do not > call either offline_pages() or online_pages(). > > The operations they perform are the following ones: > > 1) Create the linear mapping in case the memory is not private > 2) Initialize the pages and add the sections > 3) Move the pages to ZONE_DEVICE > > Due to this particular handling of hot-add/remove memory from HMM/devm, > I think it would be nice to provide a helper function in order to > make this cleaner, and not populate other regions with code > that should belong to memory-hotplug. > > The helpers are named: > > del_device_memory > add_device_memory > > The idea is that add_device_memory will be in charge of: > > a) call either arch_add_memory() or add_pages(), depending on whether > we want a linear mapping > b) online the memory sections that correspond to the pfn range > c) call move_pfn_range_to_zone() being zone ZONE_DEVICE to > expand zone/pgdat spanned pages and initialize its pages > > del_device_memory, on the other hand, will be in charge of: > > a) offline the memory sections that correspond to the pfn range > b) call shrink_zone_pgdat_pages(), which shrinks node/zone spanned pages. > c) call either arch_remove_memory() or __remove_pages(), depending on > whether we need to tear down the linear mapping or not > > The reason behind step b) from add_device_memory() and step a) > from del_device_memory is that now find_smallest/biggest_section_pfn > will have to check for online sections, and not for valid sections as > they used to do, because we call offline_mem_sections() in > offline_pages(). > > In order to split up better the patches and ease the review, > this patch will only make a) case work for add_device_memory(), > and case c) for del_device_memory. > > The other cases will be added in the next patch. > > These two functions have to be called from devm/HMM code: > > dd_device_memory: > - devm_memremap_pages() > - hmm_devmem_pages_create() > > del_device_memory: > - hmm_devmem_release > - devm_memremap_pages_release > > One thing I do not know is whether we can move kasan calls out of the > hotplug lock or not. > If we can, we could move the hotplug lock within add/del_device_memory(). > > Signed-off-by: Oscar Salvador <osalvador@xxxxxxx> > --- > include/linux/memory_hotplug.h | 11 +++++++++++ > kernel/memremap.c | 11 ++++------- > mm/hmm.c | 33 +++++++++++++++++---------------- > mm/memory_hotplug.c | 41 +++++++++++++++++++++++++++++++++++++++++ > 4 files changed, 73 insertions(+), 23 deletions(-) This collides with the refactoring of hmm, to be done in terms of devm_memremap_pages(). I'd rather not introduce another common function *beneath* hmm and devm_memremap_pages() and rather make devm_memremap_pages() the common function. I plan to resubmit that cleanup after Plumbers. So, unless I'm misunderstanding some other benefit a nak from me on this patch as it stands currently.
