[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] libxc: try to find last used pfn when migrating
On Fri, 2015-11-27 at 16:11 +0100, Juergen Gross wrote: > On 27/11/15 16:01, David Vrabel wrote: > > On 27/11/15 14:50, Juergen Gross wrote: > > > For migration the last used pfn of a guest is needed to size the > > > logdirty bitmap and as an upper bound of the page loop. Unfortunately > > > there are pv-kernels advertising a much higher maximum pfn as they > > > are really using in order to support memory hotplug. This will lead > > > to allocation of much more memory in Xen tools during migration as > > > really needed. > > > > > > Try to find the last used guest pfn of a pv-domu by scanning the p2m > > > tree from the last entry towards it's start and search for an entry > > > not being invalid. > > > > > > Normally the mid pages of the p2m tree containing all invalid entries > > > are being reused, so we can just scan the top page for identical > > > entries and skip them but the first one. > > > > This has been fixed in Linux by "x86/xen/p2m: hint at the last > > populated > > P2M entry" 98dd166ea3a3c3b57919e20d9b0d1237fcd0349d which is tagged for > > stable. > > > > Do we really need a toolstack fix as well? > > xl migrate will use much less resources for a domain with a 3.x kernel > started with max_mem being much larger than mem. E.g. in case you start > a domain on a small stand-by system and migrate it later to the large > production system and want to balloon it up there. > > Additionally there was a discussion this week on irc regarding this > topic and concern was raised this could block dom0 responsiveness. We certainly want the toolstack domain to be more resilient in the face of ludicrous guest-supplied numbers than it is today. Ian. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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