On Wed, 2013-10-09 at 14:14 -0700, H. Peter Anvin wrote: > On 10/09/2013 02:11 PM, Tejun Heo wrote: > > Hello, Toshi. > > > > On Wed, Oct 09, 2013 at 02:58:31PM -0600, Toshi Kani wrote: > >> Let's not assume that memory hotplug is always a niche feature for huge > >> & special systems. It may be a niche to begin with, but it could be > >> supported on VMs, which allows anyone to use. Vasilis has been working > >> on KVM to support memory hotplug. > > > > I'm not saying hotplug will always be niche. I'm saying the approach > > we're currently taking is. It seems fairly inflexible to hang the > > whole thing on NUMA nodes. What does the planned kvm support do? > > Splitting SRAT nodes so that it can do both actual NUMA node > > distribution and hotplug granuliarity? IIRC I asked a couple times > > what the long term plan was for this feature and there doesn't seem to > > be any road map for this thing to become a full solution. Unless I > > misunderstood, this is more of "let's put out the fire as there > > already are (or gonna be) machines which can do it" kinda thing, which > > is fine too. My point is that it doesn't make a lot of sense to > > change boot sequence invasively to accomodate that. > > > > I would also argue that in the VM scenario -- and arguable even in the > hardware scenario -- the right thing is to not expose the flexible > memory in the e820/EFI tables, and instead have it hotadded (possibly > *immediately* so) on boot. This avoids both the boot time funnies as > well as the scaling issues with metadata. That's a good idea! It will work just fine if firmware is written in such a way. However, since the most (if not all) firmware integrates and exposes all memory at boot, we still need to support this regular scenario as well. > The whole reason for VMs wanting this is because ballooning doesn't > scale with regards to metadata. Agreed. Thanks, -Toshi -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>