Re: [Qemu-devel] [PATCH] memory: unref the memory region in simplify flatview

[Paolo Bonzini <pbonzini@redhat.com>]

On 12/07/19 08:52, Wang King wrote:
> From: King Wang<king.wang@huawei.com>
> 
> The memory region reference is increased when insert a range
> into flatview range array, then decreased by destroy flatview.
> If some flat range merged by flatview_simplify, the memory region
> reference can not be decreased by destroy flatview any more.
> 
> In this case, start virtual machine by the command line:
> qemu-system-x86_64
> -name guest=ubuntu,debug-threads=on
> -machine pc,accel=kvm,usb=off,dump-guest-core=off
> -cpu host
> -m 16384
> -realtime mlock=off
> -smp 8,sockets=2,cores=4,threads=1
> -object memory-backend-file,id=ram-node0,prealloc=yes,mem-path=/dev/hugepages,share=yes,size=8589934592
> -numa node,nodeid=0,cpus=0-3,memdev=ram-node0
> -object memory-backend-file,id=ram-node1,prealloc=yes,mem-path=/dev/hugepages,share=yes,size=8589934592
> -numa node,nodeid=1,cpus=4-7,memdev=ram-node1
> -no-user-config
> -nodefaults
> -rtc base=utc
> -no-shutdown
> -boot strict=on
> -device piix3-usb-uhci,id=usb,bus=pci.0,addr=0x1.0x2
> -device virtio-scsi-pci,id=scsi0,bus=pci.0,addr=0x2
> -device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x3
> -drive file=ubuntu.qcow2,format=qcow2,if=none,id=drive-virtio-disk0,cache=none,aio=native
> -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
> -chardev pty,id=charserial0
> -device isa-serial,chardev=charserial0,id=serial0
> -device usb-tablet,id=input0,bus=usb.0,port=1
> -vnc 0.0.0.0:0
> -device VGA,id=video0,vgamem_mb=16,bus=pci.0,addr=0x5
> -device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x6
> -msg timestamp=on
> 
> And run the script in guest OS:
> while true
> do
>     setpci -s 00:06.0 04.b=03
> 	setpci -s 00:06.0 04.b=07
> done
> 
> I found the reference of node0 HostMemoryBackendFile is a big one.
> (gdb) p numa_info[0]->node_memdev->parent.ref
> $6 = 1636278
> (gdb)
> 
> Signed-off-by: King Wang<king.wang@huawei.com>
> ---
>  memory.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/memory.c b/memory.c
> index 480f3d989b..d8d42bdff8 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -321,7 +321,7 @@ static bool can_merge(FlatRange *r1, FlatRange *r2)
>  /* Attempt to simplify a view by merging adjacent ranges */
>  static void flatview_simplify(FlatView *view)
>  {
> -    unsigned i, j;
> +    unsigned i, j, k;
>  
>      i = 0;
>      while (i < view->nr) {
> @@ -332,6 +332,9 @@ static void flatview_simplify(FlatView *view)
>              ++j;
>          }
>          ++i;
> +        for (k = i; k < j; k++) {
> +            memory_region_unref(view->ranges[k].mr);
> +        }
>          memmove(&view->ranges[i], &view->ranges[j],
>                  (view->nr - j) * sizeof(view->ranges[j]));
>          view->nr -= j - i;
> 

Good catch.  Queued, thanks.

Paolo