On Thu, Aug 14, 2014 at 02:31:41PM +0800, zhanghailiang wrote: > On 2014/8/13 19:50, Michael S. Tsirkin wrote: > >On Wed, Aug 13, 2014 at 07:21:57PM +0800, zhanghailiang wrote: > >>If we configure qemu with realtime-mlock-on and memory-node-bind at the > >>same time, > >>Qemu will fail to start, and mbind() fails with message "Input/output > >>error". > >> > >>> From man page: > >>int mbind(void *addr, unsigned long len, int mode, > >> unsigned long *nodemask, unsigned long maxnode, > >> unsigned flags); > >>The *MPOL_BIND* mode specifies a strict policy that restricts memory > >>allocation > >>to the nodes specified in nodemask. > >>If *MPOL_MF_STRICT* is passed in flags and policy is not MPOL_DEFAULT(In > >>qemu > >>here is MPOL_BIND), then the call will fail with the error EIO if the > >>existing > >>pages in the memory range don't follow the policy. > >> > >>The memory locked ahead by mlockall can not guarantee to follow the policy > >>above, > >>And if that happens, it will result in an EIO error. > >> > >>So we should call mlock after mbind, here we adjust the place where called > >>mlock, > >>Move it to function pc_memory_init. > >> > >>Signed-off-by: xiexiangyou<xiexiang...@huawei.com> > >>Signed-off-by: zhanghailiang<zhang.zhanghaili...@huawei.com> > > > >OK but won't this still fail in case of memory hotplug? > >We set MCL_FUTURE so the same will apply?
It has already been set. > >Maybe it's enough to set MPOL_MF_MOVE? > >Does the following work for you? > > > > Hi Michael, > > I have tested memory hotplug, use virsh command like > 'virsh setmem redhat-6.4 6388608 --config --live', it is OK, and > it will not call mbind when do such memory hotplug. > but i don't know if there is command like 'memory-node hotplug' ? Using qemu monitor command: object_add memory-backend-ram,id=ram1,size=128M,host-nodes=0,policy=bind > > MPOL_MF_MOVE can work, it is more simple, but it is not perfect. It > consumes more time to *move the memory*(i guess will reconstruct > pages and copy memory)which has been locked by mlockall. The result > is VM will start slower than the above scenario. I think your patch makes sense but it doesn't work for hotplugged memory. We need MPOL_MF_MOVE, too. > > BTW, i think the follow process is clearer and more logical: > Allocate memory--->Set memory policy--->Lock memory. > > So what's your opinion? Thanks very much. > > > >--> > > > >hostmem: set MPOL_MF_MOVE > > > >When memory is allocated on a wrong node, MPOL_MF_STRICT > >doesn't move it - it just fails the allocation. > >A simple way to reproduce the failure is with mlock=on > >realtime feature. > > > >The code comment actually says: "ensure policy won't be ignored" > >so setting MPOL_MF_MOVE seems like a better way to do this. > > > >Signed-off-by: Michael S. Tsirkin<m...@redhat.com> > > > >--- > > > >diff --git a/backends/hostmem.c b/backends/hostmem.c > >index ca10c51..a9905c0 100644 > >--- a/backends/hostmem.c > >+++ b/backends/hostmem.c > >@@ -304,7 +304,7 @@ host_memory_backend_memory_complete(UserCreatable *uc, > >Error **errp) > > /* ensure policy won't be ignored in case memory is preallocated > > * before mbind(). note: MPOL_MF_STRICT is ignored on hugepages so > > * this doesn't catch hugepage case. */ > >- unsigned flags = MPOL_MF_STRICT; > >+ unsigned flags = MPOL_MF_STRICT | MPOL_MF_MOVE; > > > > /* check for invalid host-nodes and policies and give more verbose > > * error messages than mbind(). */ > > >