Gerrit Huizenga wrote:
On Wed, 02 Nov 2005 19:50:15 +1100, Nick Piggin wrote:
Isn't the solution for your hypervisor problem to dish out pages of
the same size that are used by the virtual machines. Doesn't this
provide you with a nice, 100% solution that doesn't add complexity
where it isn't needed?
So do you see the problem with fragementation if the hypervisor is
handing out, say, 1 MB pages? Or, more likely, something like 64 MB
pages? What are the chances that an entire 64 MB page can be freed
on a large system that has been up a while?
I see the problem, but if you want to be able to shrink memory to a
given size, then you must either introduce a hard limit somewhere, or
have the hypervisor hand out guest sized pages. Use zones, or Xen?
And, if you create zones, you run into all of the zone rebalancing
problems of ZONE_DMA, ZONE_NORMAL, ZONE_HIGHMEM. In that case, on
any long running system, ZONE_HOTPLUGGABLE has been overwhelmed with
random allocations, making almost none of it available.
If there are zone rebalancing problems[*], then it would be great to
have more users of zones because then they will be more likely to get
fixed.
[*] and there are, sadly enough - see the recent patches I posted to
lkml for example. But I'm fairly confident that once the particularly
silly ones have been fixed, zone balancing will no longer be a
derogatory term as has been thrown around (maybe rightly) in this
thread!
--
SUSE Labs, Novell Inc.
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