qemu: Honor hugepages for UMA domains

https://bugzilla.redhat.com/show_bug.cgi?id=1135396

There are two ways how to tell qemu to use huge pages. The first one
is suitable for domains with NUMA nodes: the path to hugetlbfs mount
is appended to NUMA node definition on the command line. The second
one is suitable for UMA domains: here there's this global '-mem-path'
argument that accepts path to the hugetlbfs mount point. However, the
latter case was not used for all the cases that it should be. For
instance:

  <memoryBacking>
    <hugepages>
      <page size='2048' unit='KiB' nodeset='0'/>
    </hugepages>
  </memoryBacking>

didn't trigger the '-mem-path' so the huge pages - despite being
configured - were not used at all.

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

src/qemu/qemu_command.c

@@ -7686,7 +7686,7 @@ qemuBuildCommandLine(virConnectPtr conn,
     virCommandAddArg(cmd, "-m");
     def->mem.max_balloon = VIR_DIV_UP(def->mem.max_balloon, 1024) * 1024;
     virCommandAddArgFormat(cmd, "%llu", def->mem.max_balloon / 1024);
-    if (def->mem.nhugepages && !def->mem.hugepages[0].size) {
+    if (def->mem.nhugepages && (!def->cpu || !def->cpu->ncells)) {
         char *mem_path;
 
         if (!cfg->nhugetlbfs) {
@@ -7702,9 +7702,26 @@ qemuBuildCommandLine(virConnectPtr conn,
             goto error;
         }
 
-        if (!(mem_path = qemuGetDefaultHugepath(cfg->hugetlbfs,
-                                                cfg->nhugetlbfs)))
-            goto error;
+        if (def->mem.hugepages[0].size) {
+            for (j = 0; j < cfg->nhugetlbfs; j++) {
+                if (cfg->hugetlbfs[j].size == def->mem.hugepages[0].size)
+                    break;
+            }
+
+            if (j == cfg->nhugetlbfs) {
+                virReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("Unable to find any usable hugetlbfs mount for %llu KiB"),
+                               def->mem.hugepages[0].size);
+                goto error;
+            }
+
+            if (!(mem_path = qemuGetHugepagePath(&cfg->hugetlbfs[j])))
+                goto error;
+        } else {
+            if (!(mem_path = qemuGetDefaultHugepath(cfg->hugetlbfs,
+                                                    cfg->nhugetlbfs)))
+                goto error;
+        }
 
         virCommandAddArgList(cmd, "-mem-prealloc", "-mem-path",
                              mem_path, NULL);

tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages5.args

@@ -0,0 +1,7 @@
+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
+/usr/bin/qemu -S -M pc -m 1024 \
+-mem-prealloc \
+-mem-path /dev/hugepages2M/libvirt/qemu \
+-smp 2 -nographic \
+-monitor unix:/tmp/test-monitor,server,nowait -no-acpi -boot c -usb \
+-hda /dev/HostVG/QEMUGuest1 -net none -serial none -parallel none

tests/qemuxml2argvdata/qemuxml2argv-hugepages-pages5.xml

@@ -0,0 +1,32 @@
+<domain type='qemu'>
+  <name>SomeDummyHugepagesGuest</name>
+  <uuid>ef1bdff4-27f3-4e85-a807-5fb4d58463cc</uuid>
+  <memory unit='KiB'>1048576</memory>
+  <currentMemory unit='KiB'>1048576</currentMemory>
+  <memoryBacking>
+    <hugepages>
+      <page size='2048' unit='KiB'/>
+    </hugepages>
+  </memoryBacking>
+  <vcpu placement='static'>2</vcpu>
+  <os>
+    <type arch='i686' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu</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'/>
+    <controller type='ide' index='0'/>
+    <controller type='pci' index='0' model='pci-root'/>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>

tests/qemuxml2argvtest.c

@@ -688,6 +688,7 @@ mymain(void)
             QEMU_CAPS_OBJECT_MEMORY_FILE);
     DO_TEST_FAILURE("hugepages-pages4", QEMU_CAPS_MEM_PATH,
             QEMU_CAPS_OBJECT_MEMORY_RAM, QEMU_CAPS_OBJECT_MEMORY_FILE);
+    DO_TEST("hugepages-pages5", QEMU_CAPS_MEM_PATH);
     DO_TEST("nosharepages", QEMU_CAPS_MACHINE_OPT, QEMU_CAPS_MEM_MERGE);
     DO_TEST("disk-cdrom", NONE);
     DO_TEST("disk-cdrom-network-http", QEMU_CAPS_KVM, QEMU_CAPS_DEVICE,