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    Subject[PATCH 5.4 001/109] KVM: s390: reduce number of IO pins to 1
    Date
    From: Christian Borntraeger <borntraeger@de.ibm.com>

    [ Upstream commit 774911290c589e98e3638e73b24b0a4d4530e97c ]

    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@de.ibm.com>
    Reviewed-by: Cornelia Huck <cohuck@redhat.com>
    Reviewed-by: David Hildenbrand <david@redhat.com>
    Link: https://lore.kernel.org/r/20200617083620.5409-1-borntraeger@de.ibm.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    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 abe60268335d2..0fe5600a037e4 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 */
    --
    2.25.1


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