Messages in this thread | | | Date | Wed, 02 Nov 2005 20:37:43 +1100 | From | Nick Piggin <> | Subject | Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19 |
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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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