Messages in this thread | | | Subject | Re: [PATCH 4/4] mm, page_alloc: Only use per-cpu allocator for irq-safe requests | From | Vlastimil Babka <> | Date | Tue, 24 Jan 2017 14:16:10 +0100 |
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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@techsingularity.net> > Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com> > Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
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