Re: [libvirt] [PATCH 1/1] qemu: host NUMA hugepage policy without guest NUMA

At the moment, guests that are backed by hugepages in the host are only able to use policy to control the placement of those hugepages on a per-(guest-)CPU basis. Policy applied globally is ignored. Such guests would use <memoryBacking><hugepages/></memoryBacking> and a <numatune> block with <memory mode=... nodeset=.../> but no <memnode .../> elements. This patch corrects this by, in this specific case, changing the QEMU command line from "-mem-prealloc -mem-path=..." (which cannot specify NUMA policy) to "-object memory-backend-file ..." (which can). Note: This is not visible to the guest and does not appear to create a migration incompatibility.

Signed-off-by: Sam Bobroff <sam.bobroff(a)au1.ibm.com&gt; --- There was some discussion leading up to this patch, here: https://www.redhat.com/archives/libvir-list/2016-October/msg00033.html During that discussion it seemed that fixing this issue would cause migration incompatibility but after some careful testing, it appears that it only does when a memory-backend object is attached to a guest NUMA node and that is not the case here. If only one is created, and used globally (not attached via mem=<id>), the migration data does not seem to be changed and so it seems reasonable to try something like this patch. This patch does work for my test cases but I don't claim a deep understanding of the libvirt code so this is at least partly a RFC. Comments welcome :-) Cheers, Sam. src/qemu/qemu_command.c | 55 ++++++++++++++++++++++++++++++++++++++++--------- src/qemu/qemu_command.h | 2 +- 2 files changed, 46 insertions(+), 11 deletions(-) diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c index 0804133..c28c8f2 100644 --- a/src/qemu/qemu_command.c +++ b/src/qemu/qemu_command.c @@ -3143,7 +3143,7 @@ qemuBuildMemoryBackendStr(unsigned long long size, int guestNode, virBitmapPtr userNodeset, virBitmapPtr autoNodeset, - virDomainDefPtr def, + const virDomainDefPtr def, virQEMUCapsPtr qemuCaps, virQEMUDriverConfigPtr cfg, const char **backendType, @@ -7129,12 +7129,18 @@ qemuBuildSmpCommandLine(virCommandPtr cmd, static int qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg, - const virDomainDef *def, + const virDomainDefPtr def,

virQEMUCapsPtr qemuCaps, - virCommandPtr cmd) + virCommandPtr cmd, + virBitmapPtr auto_nodeset) { const long system_page_size = virGetSystemPageSizeKB(); char *mem_path = NULL; + virBitmapPtr nodemask = NULL; + const char *backendType = NULL; + char *backendStr = NULL; + virJSONValuePtr props; + int rv = -1; /* * No-op if hugepages were not requested. @@ -7159,18 +7165,47 @@ qemuBuildMemPathStr(virQEMUDriverConfigPtr cfg, if (qemuGetHupageMemPath(cfg, def->mem.hugepages[0].size, &mem_path) < 0) return -1; - virCommandAddArgList(cmd, "-mem-prealloc", "-mem-path", mem_path, NULL); + if (virDomainNumatuneMaybeGetNodeset(def->numa, auto_nodeset, + &nodemask, -1) < 0) + return -1; + if (nodemask && virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_FILE)) { + props = virJSONValueNewObject(); + if (qemuBuildMemoryBackendStr(virDomainDefGetMemoryInitial(def), + 0, -1, NULL, auto_nodeset, + def, qemuCaps, cfg, &backendType, + &props, false) < 0) + goto cleanup; + if (!(backendStr = virQEMUBuildObjectCommandlineFromJSON(backendType, + "mem", + props))) + goto cleanup; + virCommandAddArgList(cmd, "-object", backendStr, NULL);

+ rv = 0; +cleanup: + VIR_FREE(backendStr); + VIR_FREE(props); + } + else { + if (nodemask || 1)

+ virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s", + _("Memory file backend objects are " + "unsupported by QEMU binary. Global NUMA " + "hugepage policy will be ignored."));