qemu: Implement memoryBacking/discard

https://bugzilla.redhat.com/show_bug.cgi?id=1480668

QEMU has this new feature memory-backend-file.discard-data=yes
which is a nifty optimization. Basically, when qemu is quitting
or on memory hotplug it calls munmap() and close() on the file
that is backing the memory. However, this does not mean kernel
won't stop touching that part of memory. It still might. With
this feature enabled we tell kernel: "we don't need this memory
nor data stored in it". This makes kernel drop the memory
immediately without trying to sync memory with the mapped file.

Unfortunately, this cannot be turned on by default because we
can't be sure when users really don't care about what happens to
data after qemu dies. So it has to be opt-in. As usual, there are
three places where one can configure memory attributes. This
patch adds the feature to all of them.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 81a9811d14d63873f23848dc5e13aa3aa75d4c25..11ad77f145f481eb48049247d235e7bb084d5ce2 100644 (file)
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -3029,6 +3029,7 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
     unsigned long long pagesize = mem->pagesize;
     bool needHugepage = !!pagesize;
     bool useHugepage = !!pagesize;
+    int discard = mem->discard;
 
     /* The difference between @needHugepage and @useHugepage is that the latter
      * is true whenever huge page is defined for the current memory cell.
@@ -3039,8 +3040,7 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
     *backendProps = NULL;
     *backendType = NULL;
 
-    if (memAccess == VIR_DOMAIN_MEMORY_ACCESS_DEFAULT &&
-        mem->targetNode >= 0) {
+    if (mem->targetNode >= 0) {
         /* memory devices could provide a invalid guest node */
         if (mem->targetNode >= virDomainNumaGetNodeCount(def->numa)) {
             virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
@@ -3050,12 +3050,19 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
             return -1;
         }
 
-        memAccess = virDomainNumaGetNodeMemoryAccessMode(def->numa, mem->targetNode);
+        if (memAccess == VIR_DOMAIN_MEMORY_ACCESS_DEFAULT)
+            memAccess = virDomainNumaGetNodeMemoryAccessMode(def->numa, mem->targetNode);
+
+        if (discard == VIR_TRISTATE_BOOL_ABSENT)
+            discard = virDomainNumaGetNodeDiscard(def->numa, mem->targetNode);
     }
 
     if (memAccess == VIR_DOMAIN_MEMORY_ACCESS_DEFAULT)
         memAccess = def->mem.access;
 
+    if (discard == VIR_TRISTATE_BOOL_ABSENT)
+        discard = def->mem.discard;
+
     if (virDomainNumatuneGetMode(def->numa, mem->targetNode, &mode) < 0 &&
         virDomainNumatuneGetMode(def->numa, -1, &mode) < 0)
         mode = VIR_DOMAIN_NUMATUNE_MEM_STRICT;
@@ -3143,6 +3150,20 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
                                   NULL) < 0)
             goto cleanup;
 
+        if (!mem->nvdimmPath &&
+            discard == VIR_TRISTATE_BOOL_YES) {
+            if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_FILE_DISCARD)) {
+                virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                               _("this QEMU doesn't support memory discard"));
+                goto cleanup;
+            }
+
+            if (virJSONValueObjectAdd(props,
+                                      "B:discard-data", true,
+                                      NULL) < 0)
+                goto cleanup;
+        }
+
         switch (memAccess) {
         case VIR_DOMAIN_MEMORY_ACCESS_SHARED:
             if (virJSONValueObjectAdd(props, "b:share", true, NULL) < 0)

diff --git a/tests/qemuxml2argvdata/hugepages-pages.args b/tests/qemuxml2argvdata/hugepages-pages.args
index 7ece0272a0cff6c60b98cc96af616ce60f5bfbea..b52cd581d5f966c7bf7e8a6dce4ecc40a23daf1c 100644 (file)
--- a/tests/qemuxml2argvdata/hugepages-pages.args
+++ b/tests/qemuxml2argvdata/hugepages-pages.args
@@ -11,20 +11,20 @@ QEMU_AUDIO_DRV=none \
 -m 4096 \
 -smp 4,sockets=4,cores=1,threads=1 \
 -object memory-backend-file,id=ram-node0,prealloc=yes,\
-mem-path=/dev/hugepages1G/libvirt/qemu/-1-QEMUGuest1,size=1073741824,\
-host-nodes=0-3,policy=bind \
+mem-path=/dev/hugepages1G/libvirt/qemu/-1-QEMUGuest1,discard-data=yes,\
+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,size=1073741824,\
 host-nodes=0-3,policy=bind \
 -numa node,nodeid=1,cpus=1,memdev=ram-node1 \
 -object memory-backend-file,id=ram-node2,prealloc=yes,\
-mem-path=/dev/hugepages1G/libvirt/qemu/-1-QEMUGuest1,size=1073741824,\
-host-nodes=0-3,policy=bind \
+mem-path=/dev/hugepages1G/libvirt/qemu/-1-QEMUGuest1,discard-data=yes,\
+size=1073741824,host-nodes=0-3,policy=bind \
 -numa node,nodeid=2,cpus=2,memdev=ram-node2 \
 -object memory-backend-file,id=ram-node3,prealloc=yes,\
-mem-path=/dev/hugepages1G/libvirt/qemu/-1-QEMUGuest1,size=1073741824,\
-host-nodes=3,policy=bind \
+mem-path=/dev/hugepages1G/libvirt/qemu/-1-QEMUGuest1,discard-data=yes,\
+size=1073741824,host-nodes=3,policy=bind \
 -numa node,nodeid=3,cpus=3,memdev=ram-node3 \
 -uuid c7a5fdbd-edaf-9455-926a-d65c16db1809 \
 -display none \

diff --git a/tests/qemuxml2argvdata/hugepages-pages3.args b/tests/qemuxml2argvdata/hugepages-pages3.args
index 2fc701ca22fb99e2b21fd4eb6cf91f2b3702f36a..d55265cdd8b76eb2accfcd285bd4f0bcf7a53c80 100644 (file)
--- a/tests/qemuxml2argvdata/hugepages-pages3.args
+++ b/tests/qemuxml2argvdata/hugepages-pages3.args
@@ -13,7 +13,8 @@ QEMU_AUDIO_DRV=none \
 -object memory-backend-ram,id=ram-node0,size=268435456 \
 -numa node,nodeid=0,cpus=0,memdev=ram-node0 \
 -object memory-backend-file,id=ram-node1,prealloc=yes,\
-mem-path=/dev/hugepages1G/libvirt/qemu/-1-SomeDummyHugepagesGu,size=805306368 \
+mem-path=/dev/hugepages1G/libvirt/qemu/-1-SomeDummyHugepagesGu,\
+discard-data=yes,size=805306368 \
 -numa node,nodeid=1,cpus=1,memdev=ram-node1 \
 -uuid ef1bdff4-27f3-4e85-a807-5fb4d58463cc \
 -display none \

diff --git a/tests/qemuxml2argvdata/hugepages-pages7.args b/tests/qemuxml2argvdata/hugepages-pages7.args
index 1cb598d692abe7b237976ba8e36c558056166e8d..02a98026eb951d75f2ab44b7f99600eafc8f9928 100644 (file)
--- a/tests/qemuxml2argvdata/hugepages-pages7.args
+++ b/tests/qemuxml2argvdata/hugepages-pages7.args
@@ -18,7 +18,8 @@ mem-path=/dev/hugepages1G/libvirt/qemu/-1-fedora,size=1073741824,\
 host-nodes=1-3,policy=bind \
 -device pc-dimm,node=0,memdev=memdimm0,id=dimm0,slot=0 \
 -object memory-backend-file,id=memdimm1,prealloc=yes,\
-mem-path=/dev/hugepages2M/libvirt/qemu/-1-fedora,share=no,size=536870912 \
+mem-path=/dev/hugepages2M/libvirt/qemu/-1-fedora,discard-data=yes,share=no,\
+size=536870912 \
 -device pc-dimm,node=0,memdev=memdimm1,id=dimm1,slot=1 \
 -uuid 63840878-0deb-4095-97e6-fc444d9bc9fa \
 -display none \

diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 756ca7a77f3b39089cddae664572a24b477250a9..d4d64b0d2190ea5a088ec5bac3d3db9c73819297 100644 (file)
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -919,11 +919,13 @@ mymain(void)
             QEMU_CAPS_OBJECT_MEMORY_FILE);
     DO_TEST("hugepages-pages",
             QEMU_CAPS_OBJECT_MEMORY_RAM,
-            QEMU_CAPS_OBJECT_MEMORY_FILE);
+            QEMU_CAPS_OBJECT_MEMORY_FILE,
+            QEMU_CAPS_OBJECT_MEMORY_FILE_DISCARD);
     DO_TEST("hugepages-pages2", QEMU_CAPS_OBJECT_MEMORY_RAM,
             QEMU_CAPS_OBJECT_MEMORY_FILE);
     DO_TEST("hugepages-pages3", QEMU_CAPS_OBJECT_MEMORY_RAM,
-            QEMU_CAPS_OBJECT_MEMORY_FILE);
+            QEMU_CAPS_OBJECT_MEMORY_FILE,
+            QEMU_CAPS_OBJECT_MEMORY_FILE_DISCARD);
     DO_TEST("hugepages-shared",
             QEMU_CAPS_OBJECT_MEMORY_RAM,
             QEMU_CAPS_OBJECT_MEMORY_FILE);
@@ -933,7 +935,8 @@ mymain(void)
     DO_TEST("hugepages-pages5", NONE);
     DO_TEST("hugepages-pages6", NONE);
     DO_TEST("hugepages-pages7",
-            QEMU_CAPS_DEVICE_PC_DIMM, QEMU_CAPS_OBJECT_MEMORY_FILE);
+            QEMU_CAPS_DEVICE_PC_DIMM, QEMU_CAPS_OBJECT_MEMORY_FILE,
+            QEMU_CAPS_OBJECT_MEMORY_FILE_DISCARD);
     DO_TEST("hugepages-memaccess", QEMU_CAPS_OBJECT_MEMORY_FILE,
             QEMU_CAPS_OBJECT_MEMORY_RAM, QEMU_CAPS_DEVICE_PC_DIMM,
             QEMU_CAPS_NUMA);