Re: [Qemu-devel] [RFC PATCH 1/1] ceph/rbd block driver for qemu-kvm

[Avi Kivity]

On 05/25/2010 06:01 PM, Anthony Liguori wrote:
> On 05/25/2010 10:00 AM, Avi Kivity wrote:
> > The latter.  Why is it less important?  If you don't inherit the 
> > memory, you can't access it.
> >
> > > You can also pass /dev/shm fd's via SCM_RIGHTs to establish shared 
> > > memory segments dynamically.
> >
> > Doesn't work for anonymous memory.
>
> What's wrong with /dev/shm memory?

The kernel treats anonymous and nonymous memory differently for swapping 
(see /proc/sys/vm/swappiness); transparent hugepages won't work for 
/dev/shm (though it may be argued that that's a problem with thp); setup 
(/dev/shm defaults to half memory IIRC, we want mem+swap); different 
cgroup handling; somewhat clunky (a minor concern to be sure).

Nothing is a killer, but we should prefer anonymous memory.

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