[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Proposed new "memory capacity claim" hypercall/feature
>>> On 07.11.12 at 23:17, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx> wrote: > It appears that the attempt to use 2MB and 1GB pages is done in > the toolstack, and if the hypervisor rejects it, toolstack tries > smaller pages. Thus, if physical memory is highly fragmented > (few or no order>=9 allocations available), this will result > in one hypercall per 4k page so a 256GB domain would require > 64 million hypercalls. And, since AFAICT, there is no sane > way to hold the heap_lock across even two hypercalls, speeding > up the in-hypervisor allocation path, by itself, will not solve > the TOCTOU race. No, even in the absence of large pages, the tool stack will do 8M allocations, just without requesting them to be contiguous. Whether 8M is a suitable value is another aspect; that value may predate hypercall preemption, and I don't immediately see why the tool stack shouldn't be able to request larger chunks (up to the whole amount at once). Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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