On Fri 04-06-21 09:41:45, Oscar Salvador wrote: > On Thu, Jun 03, 2021 at 02:45:13PM +0200, Michal Hocko wrote: [...] > > But the primary question is whether anybody actually cares about > > potential races in the first place. > > I have been checking move_freepages_block() and alloc_contig_pages(), which > are two of the functions that call zone_spans_pfn(). > > move_freepages_block() uses it in a way to align the given pfn to pageblock > top and bottom, and then check that aligned pfns are still within the same zone. > From a memory-hotplug perspective that's ok as we know that we are offlining > PAGES_PER_SECTION (which implies whole pageblocks). > > alloc_contig_pages() (used by the hugetlb gigantic allocator) runs through a > node's zonelist and checks whether zone->zone_start_pfn + nr_pages stays within > the same zone. > IMHO, the race with zone_spans_last_pfn() vs mem-hotplug would not be that bad, > as it will be caught afters by e.g: __alloc_contig_pages when pages cannot be > isolated because they are offline etc. > > So, I would say we do not really need the lock, but I might be missing something. > But if we chose to care about this, then the locking should be done right, not > half-way as it is right now. That is my understanding as well. -- Michal Hocko SUSE Labs
