Re: [Qemu-devel] [PATCH V8 1/4] mem: add share parameter to memory-backend-ram

[Eduardo Habkost]

On Wed, Jan 31, 2018 at 11:10:07PM +0200, Michael S. Tsirkin wrote:
> On Wed, Jan 31, 2018 at 06:40:59PM -0200, Eduardo Habkost wrote:
> > On Wed, Jan 17, 2018 at 11:54:18AM +0200, Marcel Apfelbaum wrote:
> > > Currently only file backed memory backend can
> > > be created with a "share" flag in order to allow
> > > sharing guest RAM with other processes in the host.
> > > 
> > > Add the "share" flag also to RAM Memory Backend
> > > in order to allow remapping parts of the guest RAM
> > > to different host virtual addresses. This is needed
> > > by the RDMA devices in order to remap non-contiguous
> > > QEMU virtual addresses to a contiguous virtual address range.
> > > 
> > 
> > Why do we need to make this configurable?  Would anything break
> > if MAP_SHARED was always used if possible?
> 
> See Documentation/vm/numa_memory_policy.txt for a list
> of complications.

Ew.

> 
> Maybe we should more of an effort to detect and report these
> issues.

Probably.  Having other features breaking silently when using
pvrdma doesn't sound good.  We must at least document those
problems in the documentation for memory-backend-ram.

BTW, what's the root cause for requiring HVAs in the buffer?  Can
this be fixed?

-- 
Eduardo