[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Proposed new "memory capacity claim" hypercall/feature
> From: Jan Beulich [mailto:JBeulich@xxxxxxxx] > Sent: Thursday, November 08, 2012 6:49 AM > To: Keir Fraser > Cc: Olaf Hering; IanCampbell; George Dunlap; Ian Jackson; George Shuklin; > DarioFaggioli; xen- > devel@xxxxxxxxxxxxx; Dan Magenheimer; Konrad Rzeszutek Wilk; Kurt Hackel; > Mukesh Rathor; Zhigang Wang; > TimDeegan > Subject: Re: Proposed new "memory capacity claim" hypercall/feature > > >>> On 08.11.12 at 11:50, Keir Fraser <keir@xxxxxxx> wrote: > > On 08/11/2012 09:47, "Jan Beulich" <JBeulich@xxxxxxxx> wrote: > >> The only thing that indeed is - on non-preemptible kernels - done > >> only on exit to user mode is the eventual entering of the scheduler. > > > > That alone may still be an argument for restricting the batch size from the > > toolstack? > > Yes, this clearly prohibits unlimited batches. But not being able to > schedule should be less restrictive than not being able to run > softirqs, so I'd still put under question whether the limit shouldn't > be bumped. Wait, please define unlimited. I think we are in agreement from previous discussion that, to solve the TOCTOU race, the heap_lock must be held for the entire allocation for a domain creation. True? So unless the limit is "bumped" to handle the largest supported physical memory size for a domain AND the allocation code in the hypervisor is rewritten to hold the heap_lock while allocating the entire extent, bumping the limit doesn't help the TOCTOU race, correct? Further, holding the heap_lock not only stops scheduling of this pcpu, but also blocks other domains/pcpus from doing any micro-allocations at all. True? Sorry if I am restating the obvious, but I am red-faced about the huge-number-of-hypercalls mistake, so want to ensure if I am understanding. Dan P.S. For PV domains, doesn't the toolstack already use a batch of up to 2^20 pages? (Or maybe I am misunderstanding/misreading the code in arch_setup_meminit() in xc_dom_x86.c?) _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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