Re: [libvirt] [PATCH] add flag to enforce hugepage backing of guest RAM

On Tue, Feb 04, 2014 at 11:32:47AM -0500, Marcelo Tosatti wrote: > > Add an element named "strict-hugepages" to control whether to > refuse guest initialization in case hugepage allocation cannot > be performed. > > Signed-off-by: Marcelo Tosatti <mtosatti(a)redhat.com&gt; > > diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in > index ff50214..e79f5e6 100644 > --- a/docs/formatdomain.html.in > +++ b/docs/formatdomain.html.in > @@ -632,6 +632,9 @@ > <dt><code>hugepages</code></dt> > <dd>This tells the hypervisor that the guest should have its memory > allocated using hugepages instead of the normal native page size.</dd> > + <dt><code>strict-hugepages</code></dt> > + <dd>This tells the hypervisor that the guest should refuse to start > + in case of failure to allocate guest memory with hugepages</dd> Huh, we already supply the -mem-prealloc command line flag alongside the -mem-path flag which should cause QEMU to exit if it cannot allocate all memory upfront. > +/* > + * Returns bool: whether to fail guest initialization. > + * > + */ > +static bool qemuValidateStrictHugepage(virDomainObjPtr vm, virQEMUDriverConfigPtr cfg) > +{ > + bool ret = false; > + char **maps = NULL; > + int i; > + char *buf; > + > + if (!vm->def->mem.strict_hugepages) > + return ret; > + > + ret = true; > + > + if (!vm->def->mem.hugepage_backed || !cfg->hugepagePath) { > + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s", > + _("strict huge pages depends on huge pages")); > + return ret; > + } > + > + buf = malloc(strlen(cfg->hugepagePath) + 50); > + > + /* The parser requires /proc/pid, which only exists on platforms > + * like Linux where pid_t fits in int. */ > + if ((int) vm->pid != vm->pid || > + qemuParseProcFileStrings(vm->pid, "maps", &maps) < 0) > + goto cleanup; > + > + for (i = 0; maps && maps[i]; i++) { > + char *endptr; > + unsigned long start, end; > + const char *map = maps[i]; > + bool found = false; > + > + sprintf(buf, "%s/qemu_back_mem.pc.ram.", cfg->hugepagePath); > + if (strstr(map,buf) != NULL) > + found = true; > + > + sprintf(buf, "%s/kvm.", cfg->hugepagePath); > + if (strstr(map,buf) != NULL) > + found = true; > + > + if (!found) > + continue; > + > + errno = 0; > + start = strtol(map, &endptr, 16); > + if ((errno == ERANGE && (start == LONG_MAX || start == LONG_MIN)) > + || (errno != 0 && start == 0)) { > + continue; > + } > + > + if (endptr && *endptr == '-') > + endptr++; > + > + if (!*endptr) > + continue; > + > + errno = 0; > + end = strtol(endptr, NULL, 16); > + if ((errno == ERANGE && (end == LONG_MAX || end == LONG_MIN)) > + || (errno != 0 && end == 0)) { > + continue; > + } > + > + if (end-start >= vm->def->mem.max_balloon * 1024) { > + ret = false; > + break; > + } > + } This code is really very nasty. It is both Linux specific and exposes libvirt to the private implementation detail of QEMU's backing file naming. On top of which I don't see why we need this when we're already setting -mem-prealloc to enforce exactly this.