From e04b742f74c236202b7a505c2688068969d00e65 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Tue, 5 Mar 2019 15:42:27 -0800 Subject: 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/20181119101616.8901-4-david@redhat.com Signed-off-by: David Hildenbrand Acked-by: Michael S. Tsirkin Acked-by: Dave Young Cc: "Kirill A. Shutemov" Cc: Baoquan He Cc: Omar Sandoval Cc: Arnd Bergmann Cc: Matthew Wilcox Cc: Michal Hocko Cc: Lianbo Jiang Cc: Borislav Petkov Cc: Kazuhito Hagio Cc: Alexander Duyck Cc: Alexey Dobriyan Cc: Boris Ostrovsky Cc: Christian Hansen Cc: David Rientjes Cc: Greg Kroah-Hartman Cc: Haiyang Zhang Cc: Jonathan Corbet Cc: Juergen Gross Cc: Julien Freche Cc: Kairui Song Cc: Konstantin Khlebnikov Cc: "K. Y. Srinivasan" Cc: Len Brown Cc: Michal Hocko Cc: Mike Rapoport Cc: Miles Chen Cc: Nadav Amit Cc: Naoya Horiguchi Cc: Pankaj gupta Cc: Pavel Machek Cc: Pavel Tatashin Cc: Rafael J. Wysocki Cc: "Rafael J. Wysocki" Cc: Stefano Stabellini Cc: Stephen Hemminger Cc: Stephen Rothwell Cc: Vitaly Kuznetsov Cc: Vlastimil Babka Cc: Xavier Deguillard Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/crash_core.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'kernel') 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(); -- cgit v1.2.3