On 11/19/18 at 11:16am, David Hildenbrand wrote: > Right now, pages inflated as part of a balloon driver will be dumped > by dump tools like makedumpfile. While XEN is able to check in the > crash kernel whether a certain pfn is actuall backed by memory in the > hypervisor (see xen_oldmem_pfn_is_ram) and optimize this case, dumps of > other balloon inflated memory will essentially result in zero pages getting > allocated by the hypervisor and the dump getting filled with this data. > > The allocation and reading of zero pages can directly be avoided if a > dumping tool could know which pages only contain stale information not to > be dumped. > > We now have PG_offline which can be (and already is by virtio-balloon) > used for marking pages as logically offline. Follow up patches will > make use of this flag also in other balloon implementations. > > Let's export PG_offline via PAGE_OFFLINE_MAPCOUNT_VALUE, so > makedumpfile can directly skip pages that are logically offline and the > content therefore stale. > > Please note that this is also helpful for a problem we were seeing under > Hyper-V: Dumping logically offline memory (pages kept fake offline while > onlining a section via online_page_callback) would under some condicions > result in a kernel panic when dumping them. > > Cc: Andrew Morton <a...@linux-foundation.org> > Cc: Dave Young <dyo...@redhat.com> > Cc: "Kirill A. Shutemov" <kirill.shute...@linux.intel.com> > Cc: Baoquan He <b...@redhat.com> > Cc: Omar Sandoval <osan...@fb.com> > Cc: Arnd Bergmann <a...@arndb.de> > Cc: Matthew Wilcox <wi...@infradead.org> > Cc: Michal Hocko <mho...@suse.com> > Cc: "Michael S. Tsirkin" <m...@redhat.com> > Cc: Lianbo Jiang <liji...@redhat.com> > Cc: Borislav Petkov <b...@alien8.de> > Cc: Kazuhito Hagio <k-ha...@ab.jp.nec.com> > Signed-off-by: David Hildenbrand <da...@redhat.com> > --- > kernel/crash_core.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/crash_core.c b/kernel/crash_core.c > index 933cb3e45b98..093c9f917ed0 100644 > --- a/kernel/crash_core.c > +++ b/kernel/crash_core.c > @@ -464,6 +464,8 @@ static int __init crash_save_vmcoreinfo_init(void) > VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE); > #ifdef CONFIG_HUGETLB_PAGE > VMCOREINFO_NUMBER(HUGETLB_PAGE_DTOR); > +#define PAGE_OFFLINE_MAPCOUNT_VALUE (~PG_offline) > + VMCOREINFO_NUMBER(PAGE_OFFLINE_MAPCOUNT_VALUE); > #endif > > arch_crash_save_vmcoreinfo(); > -- > 2.17.2 >
Acked-by: Dave Young <dyo...@redhat.com> Thanks Dave _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
