[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC PATCH] page_alloc: use first half of higher order chunks when halving
On Mon, Apr 14, 2014 at 09:51:34AM +0100, Jan Beulich wrote: > >>> On 13.04.14 at 23:32, <tim@xxxxxxx> wrote: > > (c) If for some reason the current hypercall API is not sufficient > > for dom0 to get what it wants, we should consider adding some new > > operation/flag/mode somewhere. But since AFAIK there's already > > another path in linux that allocates contiguous DMA buffers > > for device drivers, presumably this isn't the case. > > And it should be kept in mind that requesting contiguous memory > shouldn't be done at will, as it may end up exhausting the portion > of memory intended for DMA-style allocations (SWIOTLB / DMA- > coherent allocations in Linux). I.e. neither Dom0 nor DomU should > be trying to populate large parts of their memory with contiguous > allocation requests to the hypervisor. They may, if they so desire, > go and re-arrange their P2M mapping (solely based on what they > got handed by doing order-0 allocations). I did try that at some point - and it did not work. The reason for trying this was that during the E820 parsing we would find the MMIO holes/gaps and instead of doing the 'XENMEM_decrease_reservation'/ 'XENMEM_populate_physmap' dance I thought I could just swap the P2M entries. That was OK, but the M2P lookup table was not too thrilled with this. Perhaps I should have used another hypercall to re-arrange the M2P? I think I did try 'XENMEM_exchange' but that is not the right call either. Perhaps I should use XENMEM_remove_from_physmap/XENMEM_add_to_physmap combo ? > > Jan > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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