kexec: export PG_offline to VMCOREINFO

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.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Acked-by: Michael S. Tsirkin <[email protected]>
Acked-by: 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: Lianbo Jiang <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Kazuhito Hagio <[email protected]>
Cc: Alexander Duyck <[email protected]>
Cc: Alexey Dobriyan <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: Christian Hansen <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Haiyang Zhang <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Julien Freche <[email protected]>
Cc: Kairui Song <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
Cc: "K. Y. Srinivasan" <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Miles Chen <[email protected]>
Cc: Nadav Amit <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Pankaj gupta <[email protected]>
Cc: Pavel Machek <[email protected]>
Cc: Pavel Tatashin <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Stefano Stabellini <[email protected]>
Cc: Stephen Hemminger <[email protected]>
Cc: Stephen Rothwell <[email protected]>
Cc: Vitaly Kuznetsov <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Xavier Deguillard <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 2 insertions, 0 deletions

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();