On Mon, Nov 19, 2018 at 11:16:11AM +0100, 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 <[email protected]> > Cc: Dave Young <[email protected]> > Cc: "Kirill A. Shutemov" <[email protected]> > Cc: Baoquan He <[email protected]> > Cc: Omar Sandoval <[email protected]> > Cc: Arnd Bergmann <[email protected]> > Cc: Matthew Wilcox <[email protected]> > Cc: Michal Hocko <[email protected]> > Cc: "Michael S. Tsirkin" <[email protected]> > Cc: Lianbo Jiang <[email protected]> > Cc: Borislav Petkov <[email protected]> > Cc: Kazuhito Hagio <[email protected]> > Signed-off-by: David Hildenbrand <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]> > --- > 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 _______________________________________________ devel mailing list [email protected] http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
