[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH RFC 2/2] xen: arm: Enable physical address space compression (PDX) on arm64
On Mon, 2014-09-08 at 17:32 -0700, Julien Grall wrote: > > On 04/09/14 09:40, Ian Campbell wrote: > >> I don't really understand what the function is achieving. Could you > >> explain a bit more? > > > > This is largely derived from an x86 equivalent (see srat_parse_regions, > > they are different because one walks the device tree RAM and the other > > the SRAT), so I hope Jan will correct me if I'm wrong about the > > following: > > > > What it is doing is calculating a mask which corresponds to to the bits > > that are active address bits across the valid memory addresses, i.e. a > > bit which is necessary to unambiguously represent some valid address is > > 1 and a bit which is the same for all addresses is 0. > > > > Using that mask we then find a large run of zeroes from he middle of the > > mask which by construction do not actually get used for addressing. By > > omitting those bits from the PFN we obtain a PDX which is the > > (losslessly) compressed form. > > Many thank for the explanation! No problem. Do you have an opinion on the patch now? Ian. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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