qemu: Prefer hugepages over mem source='file'

https://bugzilla.redhat.com/show_bug.cgi?id=1214369

Consider the following XML:

  <memoryBacking>
    <hugepages>
      <page size='2048' unit='KiB' nodeset='1'/>
    </hugepages>
    <source type='file'/>
    <access mode='shared'/>
  </memoryBacking>

  <numa>
    <cell id='0' cpus='0-3' memory='512000' unit='KiB'/>
    <cell id='1' cpus='4-7' memory='512000' unit='KiB'/>
  </numa>

The following cmd line is generated:

  -object
  memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qemu/ram,
  share=yes,size=524288000 -numa node,nodeid=0,cpus=0-3,memdev=ram-node0
  -object
  memory-backend-file,id=ram-node1,mem-path=/var/lib/libvirt/qemu/ram,
  share=yes,size=524288000 -numa node,nodeid=1,cpus=4-7,memdev=ram-node1

This is obviously wrong as for node 1 hugepages should have been
used. The hugepages configuration is more specific than <source
type='file'/>.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

src/qemu/qemu_command.c

@@ -3414,9 +3414,9 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
             if (VIR_STRDUP(memPath, mem->nvdimmPath) < 0)
                 goto cleanup;
             prealloc = true;
-        } else if (def->mem.source == VIR_DOMAIN_MEMORY_SOURCE_FILE) {
-            /* We can have both pagesize and mem source,
-             * then check mem source first. */
+        } else if (!pagesize && def->mem.source == VIR_DOMAIN_MEMORY_SOURCE_FILE) {
+            /* We can have both pagesize and mem source. If that's the case,
+             * prefer hugepages as those are more specific. */
             if (VIR_STRDUP(memPath, cfg->memoryBackingDir) < 0)
                 goto cleanup;
         } else {

tests/qemuxml2argvdata/qemuxml2argv-hugepages-memaccess2.args

@@ -0,0 +1,39 @@
+LC_ALL=C \
+PATH=/bin \
+HOME=/home/test \
+USER=test \
+LOGNAME=test \
+QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-i686 \
+-name QEMUGuest1 \
+-S \
+-M pc \
+-m size=4194304k,slots=16,maxmem=8388608k \
+-smp 4,sockets=4,cores=1,threads=1 \
+-object memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qemu/ram,\
+share=no,size=1073741824,host-nodes=0-3,policy=bind \
+-numa node,nodeid=0,cpus=0,memdev=ram-node0 \
+-object memory-backend-file,id=ram-node1,prealloc=yes,\
+mem-path=/dev/hugepages2M/libvirt/qemu/-1-QEMUGuest1,share=yes,size=1073741824,\
+host-nodes=0-3,policy=bind \
+-numa node,nodeid=1,cpus=1,memdev=ram-node1 \
+-object memory-backend-file,id=ram-node2,mem-path=/var/lib/libvirt/qemu/ram,\
+share=no,size=1073741824,host-nodes=0-3,policy=bind \
+-numa node,nodeid=2,cpus=2,memdev=ram-node2 \
+-object memory-backend-file,id=ram-node3,mem-path=/var/lib/libvirt/qemu/ram,\
+share=no,size=1073741824,host-nodes=3,policy=bind \
+-numa node,nodeid=3,cpus=3,memdev=ram-node3 \
+-object memory-backend-file,id=memdimm0,prealloc=yes,\
+mem-path=/dev/hugepages2M/libvirt/qemu/-1-QEMUGuest1,share=yes,size=536870912,\
+host-nodes=0-3,policy=bind \
+-device pc-dimm,node=1,memdev=memdimm0,id=dimm0,slot=0,addr=4294967296 \
+-uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 \
+-nographic \
+-nodefaults \
+-monitor unix:/tmp/lib/domain--1-QEMUGuest1/monitor.sock,server,nowait \
+-no-acpi \
+-boot c \
+-usb \
+-drive file=/dev/HostVG/QEMUGuest1,format=raw,if=none,id=drive-ide0-0-0 \
+-device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 \
+-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3

tests/qemuxml2argvdata/qemuxml2argv-hugepages-memaccess2.xml

@@ -0,0 +1,62 @@
+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <maxMemory slots='16' unit='KiB'>8388608</maxMemory>
+  <memory unit='KiB'>4194304</memory>
+  <currentMemory unit='KiB'>4194304</currentMemory>
+  <memoryBacking>
+    <hugepages>
+      <page size='2048' unit='KiB' nodeset='1'/>
+    </hugepages>
+    <source type='file'/>
+    <access mode='private'/>
+  </memoryBacking>
+  <vcpu placement='static'>4</vcpu>
+  <numatune>
+    <memory mode='strict' nodeset='0-3'/>
+    <memnode cellid='3' mode='strict' nodeset='3'/>
+  </numatune>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <cpu>
+    <numa>
+      <cell id='0' cpus='0' memory='1048576' unit='KiB'/>
+      <cell id='1' cpus='1' memory='1048576' unit='KiB' memAccess='shared'/>
+      <cell id='2' cpus='2' memory='1048576' unit='KiB' memAccess='private'/>
+      <cell id='3' cpus='3' memory='1048576' unit='KiB'/>
+    </numa>
+  </cpu>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-i686</emulator>
+    <disk type='block' device='disk'>
+      <source dev='/dev/HostVG/QEMUGuest1'/>
+      <target dev='hda' bus='ide'/>
+      <address type='drive' controller='0' bus='0' target='0' unit='0'/>
+    </disk>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
+    </controller>
+    <controller type='ide' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
+    </controller>
+    <controller type='pci' index='0' model='pci-root'/>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='virtio'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
+    </memballoon>
+    <memory model='dimm'>
+      <target>
+        <size unit='KiB'>524288</size>
+        <node>1</node>
+      </target>
+      <address type='dimm' slot='0' base='0x100000000'/>
+    </memory>
+  </devices>
+</domain>

tests/qemuxml2argvtest.c

@@ -822,6 +822,9 @@ mymain(void)
     DO_TEST("hugepages-memaccess", QEMU_CAPS_OBJECT_MEMORY_FILE,
             QEMU_CAPS_OBJECT_MEMORY_RAM, QEMU_CAPS_DEVICE_PC_DIMM,
             QEMU_CAPS_NUMA);
+    DO_TEST("hugepages-memaccess2", QEMU_CAPS_OBJECT_MEMORY_FILE,
+            QEMU_CAPS_OBJECT_MEMORY_RAM, QEMU_CAPS_DEVICE_PC_DIMM,
+            QEMU_CAPS_NUMA);
     DO_TEST("nosharepages", QEMU_CAPS_MACHINE_OPT, QEMU_CAPS_MEM_MERGE);
     DO_TEST("disk-cdrom", NONE);
     DO_TEST("disk-iscsi", NONE);

tests/qemuxml2xmloutdata/qemuxml2xmlout-hugepages-memaccess2.xml

@@ -0,0 +1 @@
+../qemuxml2argvdata/qemuxml2argv-hugepages-memaccess2.xml

tests/qemuxml2xmltest.c

@@ -420,6 +420,7 @@ mymain(void)
     DO_TEST("hugepages-pages6", NONE);
     DO_TEST("hugepages-shared", NONE);
     DO_TEST("hugepages-memaccess", NONE);
+    DO_TEST("hugepages-memaccess2", NONE);
     DO_TEST("nosharepages", NONE);
     DO_TEST("restore-v2", NONE);
     DO_TEST("migrate", NONE);