Messages in this thread | | | Date | Wed, 25 Feb 2015 17:00:07 +0100 | From | Juergen Gross <> | Subject | Re: [Xen-devel] [PATCH 06/13] xen: detect pre-allocated memory interfering with e820 map |
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On 02/25/2015 03:24 PM, David Vrabel wrote: > On 24/02/15 06:27, Juergen Gross wrote: >> On 02/19/2015 07:07 PM, David Vrabel wrote: >>> On 18/02/2015 06:51, Juergen Gross wrote: >>>> +{ >>>> + unsigned long pfn; >>>> + unsigned long area_start, area_end; >>>> + unsigned i; >>>> + >>>> + for (i = 0; i < XEN_N_RESERVED_AREAS; i++) { >>>> + >>>> + if (!xen_reserved_area[i].size) >>>> + break; >>>> + >>>> + area_start = PFN_DOWN(xen_reserved_area[i].start); >>>> + area_end = PFN_UP(xen_reserved_area[i].start + >>>> + xen_reserved_area[i].size); >>>> + if (area_start >= end_pfn || area_end <= start_pfn) >>>> + continue; >>>> + >>>> + if (area_start > start_pfn) >>>> + xen_set_identity_and_remap_chunk(start_pfn, area_start, >>>> + released, remapped); >>>> + >>>> + if (area_end < end_pfn) >>>> + xen_set_identity_and_remap_chunk(area_end, end_pfn, >>>> + released, remapped); >>>> + >>>> + *remapped += min(area_end, end_pfn) - >>>> + max(area_start, start_pfn); >>>> + >>>> + return; >>> >>> Why not defer the whole chunk that conflicts? Or for that matter defer >>> all this remapping to the last minute. >> >> There are two problems arising from this: >> >> - In the initrd case remapping would be deferred too long: the initrd >> data is still in use when device initialization is running. And we >> really want the remap to have happened before PCI space is being used. > > I'm not sure I understand what you're saying here.
I thought you wanted to defer the remapping to the point where the initrd memory is no longer being used. But the suggestion below is more clear.
> > I'm suggesting: > > 1. Reserve all holes. > > 2. Relocate (if necessary) all modules (initrd, etc.) to regions that > are RAM in the e820. > > 3. Rebuild the p2m in RAM. > > 4. Relocate frames from E820 holes/reserved to the end, free p2m pages > from the holes and replacing them with the read-only 1:1 page (where > possible). > >> - Delaying all remapping to the point where the new p2m list is in place >> would either result in a p2m list with all memory holes covered with >> individual entries as the new list is built with those holes still >> populated, ... >> The first option could easily waste significant amounts of memory (on >> my test machine with 1TB RAM this would have been about 1GB), while >> the second option would be performance critical. > > I don't understand how this wastes memory. When you relocate the > frames from the holes you can reclaim the p2m pages for the holes (and > replace them with the r/o mapped identity p2m page).
Okay, this would work, I guess.
I'll have a try with some new patches...
Juergen
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