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Date: Wed, 21 Nov 2018 10:58:04 +0800 From: Dave Young <dyoung@...hat.com> To: David Hildenbrand <david@...hat.com> Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org, devel@...uxdriverproject.org, linux-fsdevel@...r.kernel.org, linux-pm@...r.kernel.org, xen-devel@...ts.xenproject.org, kexec-ml <kexec@...ts.infradead.org>, pv-drivers@...are.com, Andrew Morton <akpm@...ux-foundation.org>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Baoquan He <bhe@...hat.com>, Omar Sandoval <osandov@...com>, Arnd Bergmann <arnd@...db.de>, Matthew Wilcox <willy@...radead.org>, Michal Hocko <mhocko@...e.com>, "Michael S. Tsirkin" <mst@...hat.com>, Lianbo Jiang <lijiang@...hat.com>, Borislav Petkov <bp@...en8.de>, Kazuhito Hagio <k-hagio@...jp.nec.com> Subject: Re: [PATCH v1 3/8] kexec: export PG_offline to VMCOREINFO On 11/19/18 at 11:16am, 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 <akpm@...ux-foundation.org> > Cc: Dave Young <dyoung@...hat.com> > Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> > Cc: Baoquan He <bhe@...hat.com> > Cc: Omar Sandoval <osandov@...com> > Cc: Arnd Bergmann <arnd@...db.de> > Cc: Matthew Wilcox <willy@...radead.org> > Cc: Michal Hocko <mhocko@...e.com> > Cc: "Michael S. Tsirkin" <mst@...hat.com> > Cc: Lianbo Jiang <lijiang@...hat.com> > Cc: Borislav Petkov <bp@...en8.de> > Cc: Kazuhito Hagio <k-hagio@...jp.nec.com> > Signed-off-by: David Hildenbrand <david@...hat.com> > --- > 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 > Acked-by: Dave Young <dyoung@...hat.com> Thanks Dave
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