On Mon, Dec 03, 2012 at 04:39:05PM -0700, Alex Williamson wrote: > Memory slots are currently a fixed resource with a relatively small > limit. When using PCI device assignment in a qemu guest it's fairly > easy to exhaust the number of available slots. I posted patches > exploring growing the number of memory slots a while ago, but it was > prior to caching memory slot array misses and thefore had potentially > poor performance. Now that we do that, Avi seemed receptive to > increasing the memory slot array to arbitrary lengths. I think we > still don't want to impose unnecessary kernel memory consumptions on > guests not making use of this, so I present again a growable memory > slot array. > > A couple notes/questions; in the previous version we had a > kvm_arch_flush_shadow() call when we increased the number of slots. > I'm not sure if this is still necessary. I had also made the x86 > specific slot_bitmap dynamically grow as well and switch between a > direct bitmap and indirect pointer to a bitmap. That may have > contributed to needing the flush. I don't remember. Do you recall what was the argument back then? (there must have been some). > I haven't done that yet here > because it seems like an unnecessary complication if we have a max > on the order of 512 or 1024 entries. A bit per slot isn't a lot of > overhead. If we want to go more, maybe we should make it switch. > That leads to the final question, we need an upper bound since this > does allow consumption of extra kernel memory, what should it be? A > PCI bus filled with assigned devices can theorically use up to 2048 > slots (32 devices * 8 functions * (6 BARs + ROM + possibly split > MSI-X BAR)). For this RFC, I don't change the max, just make it > grow up to 32 user slots. Untested on anything but x86 so far. > Thanks, Not sure. Some reasonable number based on current usage expectations? (can be increased later if necessary). -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
