On Fri 26-03-21 09:52:58, David Hildenbrand wrote: [...] > Something else to note: > > > We'll not call the memory notifier (e.g., MEM_ONLINE) for the vmemmap. The > result is that > > 1. We won't allocate extended struct pages for the range. Don't think this > is really problematic (pages are never allocated/freed, so I guess we don't > care - like ZONE_DEVICE code). Agreed. I do not think we need them. Future might disagree but let's handle it when we have a clear demand. > 2. We won't allocate kasan shadow memory. We most probably have to do it > explicitly via kasan_add_zero_shadow()/kasan_remove_zero_shadow(), see > mm/memremap.c:pagemap_range() I think this is similar to the above. Does kasan has to know about memory which will never be used for anything? > Further a locking rework might be necessary. We hold the device hotplug > lock, but not the memory hotplug lock. E.g., for get_online_mems(). Might > have to move that out online_pages. Could you be more explicit why this locking is needed? What it would protect from for vmemmap pages? -- Michal Hocko SUSE Labs
