linux-kernel - RE: [PATCH v2] makedumpfile: exclude pages that are logically offline

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Date:   Mon, 11 Mar 2019 16:40:30 +0000
From:   Kazuhito Hagio <k-hagio@...jp.nec.com>
To:     David Hildenbrand <david@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        kexec-ml <kexec@...ts.infradead.org>,
        "pv-drivers@...are.com" <pv-drivers@...are.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: RE: [PATCH v2] makedumpfile: exclude pages that are logically
 offline

-----Original Message-----
> On 27.11.18 17:32, Kazuhito Hagio wrote:
> >> Linux marks pages that are logically offline via a page flag (map count).
> >> Such pages e.g. include pages infated as part of a balloon driver or
> >> pages that were not actually onlined when onlining the whole section.
> >>
> >> While the hypervisor usually allows to read such inflated memory, we
> >> basically read and dump data that is completely irrelevant. Also, this
> >> might result in quite some overhead in the hypervisor. In addition,
> >> we saw some problems under Hyper-V, whereby we can crash the kernel by
> >> dumping, when reading memory of a partially onlined memory segment
> >> (for memory added by the Hyper-V balloon driver).
> >>
> >> Therefore, don't read and dump pages that are marked as being logically
> >> offline.
> >>
> >> Signed-off-by: David Hildenbrand <david@...hat.com>
> >
> > Thanks for the v2 update.
> > I'm going to merge this patch after the kernel patches are merged
> > and it tests fine with the kernel.
> >
> > Kazu
> 
> Hi Kazu,
> 
> the patches are now upstream. Thanks!

Tested OK at my end, too. Applied to the devel branch.

    Offline pages           : 0x0000000000002400

Thank you!
Kazu

> 
> --
> 
> Thanks,
> 
> David / dhildenb