Messages in this thread | | | Date | Thu, 20 Nov 2014 05:59:58 +0100 | From | Juergen Gross <> | Subject | Re: [PATCH V3 2/8] xen: Delay remapping memory of pv-domain |
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On 11/19/2014 08:43 PM, Konrad Rzeszutek Wilk wrote: > On Fri, Nov 14, 2014 at 06:14:06PM +0100, Juergen Gross wrote: >> On 11/14/2014 05:47 PM, Konrad Rzeszutek Wilk wrote: >>> On Fri, Nov 14, 2014 at 05:53:19AM +0100, Juergen Gross wrote: >>>> On 11/13/2014 08:56 PM, Konrad Rzeszutek Wilk wrote: >>>>>>>> + mfn_save = virt_to_mfn(buf); >>>>>>>> + >>>>>>>> + while (xen_remap_mfn != INVALID_P2M_ENTRY) { >>>>>>> >>>>>>> So the 'list' is constructed by going forward - that is from low-numbered >>>>>>> PFNs to higher numbered ones. But the 'xen_remap_mfn' is going the >>>>>>> other way - from the highest PFN to the lowest PFN. >>>>>>> >>>>>>> Won't that mean we will restore the chunks of memory in the wrong >>>>>>> order? That is we will still restore them in chunks size, but the >>>>>>> chunks will be in descending order instead of ascending? >>>>>> >>>>>> No, the information where to put each chunk is contained in the chunk >>>>>> data. I can add a comment explaining this. >>>>> >>>>> Right, the MFNs in a "chunks" are going to be restored in the right order. >>>>> >>>>> I was thinking that the "chunks" (so a set of MFNs) will be restored in >>>>> the opposite order that they are written to. >>>>> >>>>> And oddly enough the "chunks" are done in 512-3 = 509 MFNs at once? >>>> >>>> More don't fit on a single page due to the other info needed. So: yes. >>> >>> But you could use two pages - one for the structure and the other >>> for the list of MFNs. That would fix the problem of having only >>> 509 MFNs being contingous per chunk when restoring. >> >> That's no problem (see below). >> >>> Anyhow the point I had that I am worried is that we do not restore the >>> MFNs in the same order. We do it in "chunk" size which is OK (so the 509 MFNs >>> at once)- but the order we traverse the restoration process is the opposite of >>> the save process. Say we have 4MB of contingous MFNs, so two (err, three) >>> chunks. The first one we iterate is from 0->509, the second is 510->1018, the >>> last is 1019->1023. When we restore (remap) we start with the last 'chunk' >>> so we end up restoring them: 1019->1023, 510->1018, 0->509 order. >> >> No. When building up the chunks we save in each chunk where to put it >> on remap. So in your example 0-509 should be mapped at <dest>+0, >> 510-1018 at <dest>+510, and 1019-1023 at <dest>+1019. >> >> When remapping we map 1019-1023 to <dest>+1019, 510-1018 at <dest>+510 >> and last 0-509 at <dest>+0. So we do the mapping in reverse order, but >> to the correct pfns. > > Excellent! Could a condensed version of that explanation be put in the code ?
Sure.
Juergen
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