On Fri, May 09, 2014 at 11:13:50PM +0200, Paolo Bonzini wrote: > Il 09/05/2014 19:54, Eduardo Habkost ha scritto: > >On Fri, May 09, 2014 at 04:29:49PM +0800, Hu Tao wrote: > >>On Thu, May 08, 2014 at 04:51:56PM +0200, Paolo Bonzini wrote: > >>>Il 06/05/2014 11:27, Hu Tao ha scritto: > >>>>This series includes work on QOMifying the memory backends. > >>>>the idea is to delegate all properties of the memory backend to > >>>>a new QOM class hierarchy, in which the concrete classes > >>>>are hostmem-ram and hostmem-file. The backend is passed to the > >>>>machine via "-numa node,memdev=foo" where "foo" is the id of the > >>>>backend object. > >>> > >>>Hello, > >>> > >>>I noticed now that if you have the host-nodes property set Linux > >>>requires you to set a policy other than "default" too. If you don't, > >>>the mbind system call fails. > >>> > >>>What about squashing something like this? > >>> > >>>Paolo > >>> > >>>diff --git a/backends/hostmem.c b/backends/hostmem.c > >>>index d3f8476..a0a3111 100644 > >>>--- a/backends/hostmem.c > >>>+++ b/backends/hostmem.c > >>>@@ -299,12 +299,23 @@ host_memory_backend_memory_init(UserCreatable *uc, > >>>Error **errp) > >>> > >>> #ifdef CONFIG_NUMA > >>> unsigned long maxnode = find_last_bit(backend->host_nodes, MAX_NODES); > >>>+ unsigned policy = backend->policy; > >>>+ > >>>+ /* Linux does not accept MPOL_DEFAULT with nonzero bitmap, but > >>>+ * "-object memory-ram,size=128M,hostnodes=0,policy=bind" is a > >>>+ * bit of a mouthful. So if the host_nodes bitmap is nonzero, > >>>+ * pick the BIND policy. > > > >Are we sure MPOL_BIND is a better default than MPOL_INTERLEAVE or > >MPOL_PREFERRED? > > Better than MPOL_PREFERRED, yes. Better than MPOL_INTERLEAVE, I am > not sure. > > > * If policy=default is set, it is always going to be MPOL_DEFAULT. > > * If policy=bind is set, it is always going to be MPOL_BIND. > > * if policy=preferred is set, it is always going to be MPOL_PREFERRED. > > * If policy is omitted, it will be be MPOL_DEFAULT is host-nodes is > > unset, and MPOL_BIND if host_nodes is set. > > That's possible. Or we can just detect the case in > host_memory_backend_memory_init and provide a better error message > than just "Invalid argument" (aka EINVAL). We're always free to > take an error situation and make it non-error in the future, but the > reverse would be hard to do.
This one looks better. If we decide to turn implict MPOL_BIND into error in the future, it may cause a long-run guest with policy ommitted fail to start, which sounds like a compatibility problem. Regards, Hu Tao
