Hi David, On 11/22/18 at 11:06am, 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. (we export is as a macro to match how it is > done for PG_buddy. This way it is clearer that this is not actually a flag > but only a very specific mapcount value to represent page types). > > 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 <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Dave Young <dyoung@xxxxxxxxxx> > Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> > Cc: Baoquan He <bhe@xxxxxxxxxx> > Cc: Omar Sandoval <osandov@xxxxxx> > Cc: Arnd Bergmann <arnd@xxxxxxxx> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> > Cc: Lianbo Jiang <lijiang@xxxxxxxxxx> > Cc: Borislav Petkov <bp@xxxxxxxxx> > Cc: Kazuhito Hagio <k-hagio@xxxxxxxxxxxxx> > Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx> > Acked-by: Dave Young <dyoung@xxxxxxxxxx> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > --- > 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(); The patch has been merged, would you mind to send a documentation patch for the vmcoreinfo, which is added recently in Documentation/kdump/vmcoreinfo.txt A brief description about how this vmcoreinfo field is used is good to have. Thanks Dave
