On 08/05/2015 14:31, Joerg Roedel wrote: > From: Joerg Roedel <[email protected]> > > The allocation size of the kvm_irq_routing_table depends on > the number of irq routing entries because they are all > allocated with one kzalloc call. > > When the irq routing table gets bigger this requires high > order allocations which fail from time to time: > > qemu-kvm: page allocation failure: order:4, mode:0xd0 > > This patch fixes this issue by breaking up the allocation of > the table and its entries into individual kzalloc calls. > These could all be satisfied with order-0 allocations, which > are less likely to fail. > > The downside of this change is the lower performance, because > of more calls to kzalloc. But given how often kvm_set_irq_routing > is called in the lifetime of a guest, it doesn't really > matter much.
It probably doesn't matter much indeed, but can you time the difference? kvm_set_irq_routing is not too frequent, but happens enough often that we had to use a separate SRCU instance just to speed it up (see commit 719d93cd5f5, kvm/irqchip: Speed up KVM_SET_GSI_ROUTING, 2014-01-16). Paolo > Signed-off-by: Joerg Roedel <[email protected]> > --- > virt/kvm/irqchip.c | 40 ++++++++++++++++++++++++++++++++-------- > 1 file changed, 32 insertions(+), 8 deletions(-) > > diff --git a/virt/kvm/irqchip.c b/virt/kvm/irqchip.c > index 1d56a90..b56168f 100644 > --- a/virt/kvm/irqchip.c > +++ b/virt/kvm/irqchip.c > @@ -33,7 +33,6 @@ > > struct kvm_irq_routing_table { > int chip[KVM_NR_IRQCHIPS][KVM_IRQCHIP_NUM_PINS]; > - struct kvm_kernel_irq_routing_entry *rt_entries; > u32 nr_rt_entries; > /* > * Array indexed by gsi. Each entry contains list of irq chips > @@ -118,11 +117,31 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 > irq, int level, > return ret; > } > > +static void free_irq_routing_table(struct kvm_irq_routing_table *rt) > +{ > + int i; > + > + if (!rt) > + return; > + > + for (i = 0; i < rt->nr_rt_entries; ++i) { > + struct kvm_kernel_irq_routing_entry *e; > + struct hlist_node *n; > + > + hlist_for_each_entry_safe(e, n, &rt->map[i], link) { > + hlist_del(&e->link); > + kfree(e); > + } > + } > + > + kfree(rt); > +} > + > void kvm_free_irq_routing(struct kvm *kvm) > { > /* Called only during vm destruction. Nobody can use the pointer > at this stage */ > - kfree(kvm->irq_routing); > + free_irq_routing_table(kvm->irq_routing); > } > > static int setup_routing_entry(struct kvm_irq_routing_table *rt, > @@ -173,25 +192,29 @@ int kvm_set_irq_routing(struct kvm *kvm, > > nr_rt_entries += 1; > > - new = kzalloc(sizeof(*new) + (nr_rt_entries * sizeof(struct hlist_head)) > - + (nr * sizeof(struct kvm_kernel_irq_routing_entry)), > + new = kzalloc(sizeof(*new) + (nr_rt_entries * sizeof(struct > hlist_head)), > GFP_KERNEL); > > if (!new) > return -ENOMEM; > > - new->rt_entries = (void *)&new->map[nr_rt_entries]; > - > new->nr_rt_entries = nr_rt_entries; > for (i = 0; i < KVM_NR_IRQCHIPS; i++) > for (j = 0; j < KVM_IRQCHIP_NUM_PINS; j++) > new->chip[i][j] = -1; > > for (i = 0; i < nr; ++i) { > + struct kvm_kernel_irq_routing_entry *e; > + > + r = -ENOMEM; > + e = kzalloc(sizeof(*e), GFP_KERNEL); > + if (!e) > + goto out; > + > r = -EINVAL; > if (ue->flags) > goto out; > - r = setup_routing_entry(new, &new->rt_entries[i], ue); > + r = setup_routing_entry(new, e, ue); > if (r) > goto out; > ++ue; > @@ -209,6 +232,7 @@ int kvm_set_irq_routing(struct kvm *kvm, > r = 0; > > out: > - kfree(new); > + free_irq_routing_table(new); > + > return r; > } > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
