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

[Michael S. Tsirkin]

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.

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

> 
> > Moved the "share" flag to the Host Memory base class,
> > modified phys_mem_alloc to include the new parameter
> > and a new interface memory_region_init_ram_shared_nomigrate.
> > 
> > There are no functional changes if the new flag is not used.
> > 
> > Signed-off-by: Marcel Apfelbaum <address@hidden>
> [...]
> 
> -- 
> Eduardo