On 01/23/2017 04:39 PM, Mel Gorman wrote: > Many workloads that allocate pages are not handling an interrupt at a > time. As allocation requests may be from IRQ context, it's necessary to > disable/enable IRQs for every page allocation. This cost is the bulk > of the free path but also a significant percentage of the allocation > path. > > This patch alters the locking and checks such that only irq-safe allocation > requests use the per-cpu allocator. All others acquire the irq-safe > zone->lock and allocate from the buddy allocator. It relies on disabling > preemption to safely access the per-cpu structures. It could be slightly > modified to avoid soft IRQs using it but it's not clear it's worthwhile. > > This modification may slow allocations from IRQ context slightly but the main > gain from the per-cpu allocator is that it scales better for allocations > from multiple contexts. There is an implicit assumption that intensive > allocations from IRQ contexts on multiple CPUs from a single NUMA node are > rare and that the fast majority of scaling issues are encountered in !IRQ > contexts such as page faulting. It's worth noting that this patch is not > required for a bulk page allocator but it significantly reduces the overhead. > [...] > Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> > Acked-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
