On 17.06.20 13:11, Cornelia Huck wrote: > On Wed, 17 Jun 2020 13:04:52 +0200 > Christian Borntraeger <borntraeger@xxxxxxxxxx> 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. >> > > Not sure if I would count this as a real bug -- it's mostly just that a > large enough memory allocation may fail or draw the wrath of the oom > killer. It still sucks; but I'm wondering why we trigger this after > seven years. I think it is just that every kernel has a different threshold regarding "did I made forward progress in freeing enough memory before I trigger the OOM killer" I had to make it run very long with heavy overcommitment.
