On Fri, May 28, 2021 at 11:52:53AM +0200, David Hildenbrand wrote: > > > "Disable pcplists so that page isolation cannot race with freeing > > > in a way that pages from isolated pageblock are left on pcplists." > > > > > > Guess we'd then want to move the draining before start_isolate_page_range() > > > in alloc_contig_range(). > > > > > > > Or instead of draining, validate the PFN range in alloc_contig_range > > is within the same zone and if so, call zone_pcp_disable() before > > start_isolate_page_range and enable after __alloc_contig_migrate_range. > > > > We require the caller to only pass a range within a single zone, so that > should be fine. > > The only ugly thing about zone_pcp_disable() is > mutex_lock(&pcp_batch_high_lock) which would serialize all > alloc_contig_range() and even with offline_pages(). > True so it would have to be accessed if that is bad or not. If racing against offline_pages, memory is potentially being offlined in the target zone which may cause allocation failure. If racing with other alloc_contig_range calls, the two callers are potentially racing to isolate and allocate the same range. The arguement could be made that alloc_contig_ranges should be serialised within one zone to improve the allocation success rate at the potential cost of allocation latency. -- Mel Gorman SUSE Labs
