On 17.06.20 13:04, Christian Borntraeger wrote: > > > On 17.06.20 12:19, David Hildenbrand wrote: >> On 17.06.20 10:36, Christian Borntraeger wrote: >>> The current number of KVM_IRQCHIP_NUM_PINS results in an order 3 >>> allocation (32kb) for each guest start/restart. This can result in OOM >>> killer activity even with free swap when the memory is fragmented >>> enough: >>> >>> kernel: qemu-system-s39 invoked oom-killer: gfp_mask=0x440dc0(GFP_KERNEL_ACCOUNT|__GFP_COMP|__GFP_ZERO), order=3, oom_score_adj=0 >>> kernel: CPU: 1 PID: 357274 Comm: qemu-system-s39 Kdump: loaded Not tainted 5.4.0-29-generic #33-Ubuntu >>> kernel: Hardware name: IBM 8562 T02 Z06 (LPAR) >>> kernel: Call Trace: >>> kernel: ([<00000001f848fe2a>] show_stack+0x7a/0xc0) >>> kernel: [<00000001f8d3437a>] dump_stack+0x8a/0xc0 >>> kernel: [<00000001f8687032>] dump_header+0x62/0x258 >>> kernel: [<00000001f8686122>] oom_kill_process+0x172/0x180 >>> kernel: [<00000001f8686abe>] out_of_memory+0xee/0x580 >>> kernel: [<00000001f86e66b8>] __alloc_pages_slowpath+0xd18/0xe90 >>> kernel: [<00000001f86e6ad4>] __alloc_pages_nodemask+0x2a4/0x320 >>> kernel: [<00000001f86b1ab4>] kmalloc_order+0x34/0xb0 >>> kernel: [<00000001f86b1b62>] kmalloc_order_trace+0x32/0xe0 >>> kernel: [<00000001f84bb806>] kvm_set_irq_routing+0xa6/0x2e0 >>> kernel: [<00000001f84c99a4>] kvm_arch_vm_ioctl+0x544/0x9e0 >>> kernel: [<00000001f84b8936>] kvm_vm_ioctl+0x396/0x760 >>> kernel: [<00000001f875df66>] do_vfs_ioctl+0x376/0x690 >>> kernel: [<00000001f875e304>] ksys_ioctl+0x84/0xb0 >>> kernel: [<00000001f875e39a>] __s390x_sys_ioctl+0x2a/0x40 >>> kernel: [<00000001f8d55424>] system_call+0xd8/0x2c8 >>> >>> As far as I can tell s390x does not use the iopins as we bail our for >>> anything other than KVM_IRQ_ROUTING_S390_ADAPTER and the chip/pin is >>> only used for KVM_IRQ_ROUTING_IRQCHIP. So let us use a small number to >>> reduce the memory footprint. >>> >>> Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx> >>> --- >>> arch/s390/include/asm/kvm_host.h | 8 ++++---- >>> 1 file changed, 4 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h >>> index cee3cb6455a2..6ea0820e7c7f 100644 >>> --- a/arch/s390/include/asm/kvm_host.h >>> +++ b/arch/s390/include/asm/kvm_host.h >>> @@ -31,12 +31,12 @@ >>> #define KVM_USER_MEM_SLOTS 32 >>> >>> /* >>> - * These seem to be used for allocating ->chip in the routing table, >>> - * which we don't use. 4096 is an out-of-thin-air value. If we need >>> - * to look at ->chip later on, we'll need to revisit this. >>> + * These seem to be used for allocating ->chip in the routing table, which we >>> + * don't use. 1 is as small as we can get to reduce the needed memory. If we >>> + * need to look at ->chip later on, we'll need to revisit this. >>> */ >>> #define KVM_NR_IRQCHIPS 1 >>> -#define KVM_IRQCHIP_NUM_PINS 4096 >>> +#define KVM_IRQCHIP_NUM_PINS 1 >>> #define KVM_HALT_POLL_NS_DEFAULT 50000 >>> >>> /* s390-specific vcpu->requests bit members */ >>> >> >> Guess it doesn't make sense to wrap all the "->chip" handling in a >> separate set of defines. >> >> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> > > I guess this is just the most simple solution. I am asking myself if I should add > cc stable of Fixes as I was able to trigger this by having several guests with a > reboot loop and several guests that trigger memory overcommitment. > I don't think this classifies as stable material. -- Thanks, David / dhildenb
