Re: [Xen-devel] domain creation vs querying free memory (xend and xl)

[George Shuklin <george.shuklin@xxxxxxxxx>]

not sure about xl/xm, but xapi performs one start at time, so there is 
no race between domains for memory or other resources.
27.09.2012 01:17, Dan Magenheimer ÐÐÑÐÑ:
> I was asked a question that seems like it should be obvious
> but it doesn't seem to be, at least in xm-land.  I'll look
> into it further, as well as for xl, but I thought I'd ask
> first to see if there is a known answer or if this is a known
> problem:
>
> Suppose that xm/xl create is issued on a large-memory
> domain (PV or HVM or, future, PVH).  It takes awhile
> for this domain to launch and during at least part of this
> time, the toolset hasn't yet requested all of the
> required memory from the hypervisor to complete the
> launch of the domain...  or perhaps the toolset has,
> but the hypervisor is slow about calling the long sequence
> of page allocations (e.g. maybe because it is zeroing
> each page?).
>
> Then it is desired to launch a second large-memory domain.
> The tools can query Xen to see if there is sufficient RAM
> and there is, because the first launch has not yet
> allocated all the RAM assigned to it.
>
> But the second domain launch fails, possibly after
> several minutes because, actually, there isn't enough
> physical RAM for both.
>
> Does this make sense?  Should the tools "reserve"
> maxmem as a "transaction" and/or ensure that "xm/xl
> free" calls account for the entire requested amount
> of RAM?  Or maybe xl _does_ work this way?
>
> Thanks for any comments or discussion!
>
> Dan
>
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