The patch titled
Subject: kexec: export PG_offline to VMCOREINFO
has been added to the -mm tree. Its filename is
kexec-export-pg_offline-to-vmcoreinfo.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/kexec-export-pg_offline-to-vmcoreinfo.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/kexec-export-pg_offline-to-vmcoreinfo.patch
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------------------------------------------------------
From: David Hildenbrand <david@xxxxxxxxxx>
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@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
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>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/kernel/crash_core.c~kexec-export-pg_offline-to-vmcoreinfo
+++ a/kernel/crash_core.c
@@ -464,6 +464,8 @@ static int __init crash_save_vmcoreinfo_
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();
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
mm-balloon-update-comment-about-isolation-migration-compaction.patch
mm-convert-pg_balloon-to-pg_offline.patch
kexec-export-pg_offline-to-vmcoreinfo.patch
xen-balloon-mark-inflated-pages-pg_offline.patch
hv_balloon-mark-inflated-pages-pg_offline.patch
vmw_balloon-mark-inflated-pages-pg_offline.patch
pm-hibernate-use-pfn_to_online_page.patch
pm-hibernate-exclude-all-pageoffline-pages.patch
