On Mon, Sep 10, 2018 at 01:31:08PM +0200, Gert Wollny wrote: > Am Montag, den 10.09.2018, 12:53 +0200 schrieb Gerd Hoffmann: > > > > By default qemu doesn't use memfd for backing storage, you have to > > explicitly configure qemu that way (see qemu commit log of the test > > branch): > > > > qemu-system-x86_64 -m 2G > > -object memory-backend-memfd,id=ram,size=2G > > -numa node,memdev=ram" > > Thanks, but that doesn't seem to help.
Note the memory is specified twice, once with -m, once for the memory-backend-memfd object. The two must match of course (or, to be exact, the sum of all memory backends must match the total memory, but unless you want create a virtual numa machine there is no reason to have multiple memory-backends). > Are there any host kernel > configuration parameters or features that I should set (apart from > enabling udmabuf)? I'm not aware of any unusual parameters required. My config is based on rhel-7, then stripped down with localmodconfig, then enabled the bits I want in my test kernel. Oh, wait, CONFIG_MEMFD_CREATE could be the one. I guess I should add a Kconfig dependency. Even though udmabuf will build just fine without that (because memfd is basically shmem with some features on top) it doesn't buy you much if the memfd_create syscall is not available ... cheers, Gerd
