linux-kernel - Re: [PATCH RFC 0/6] mm/kdump: allow to exclude pages that are logically offline

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Message-ID: <63214D36-14FD-4080-8E35-CF2A392D6507@vmware.com>
Date:   Wed, 14 Nov 2018 23:41:16 +0000
From:   Nadav Amit <namit@...are.com>
To:     David Hildenbrand <david@...hat.com>,
        linux-mm <linux-mm@...ck.org>, Julien Freche <jfreche@...are.com>
CC:     LKML <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        xen-devel <xen-devel@...ts.xenproject.org>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>, Baoquan He <bhe@...hat.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Christian Hansen <chansen3@...co.com>,
        Dave Young <dyoung@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Jonathan Corbet <corbet@....net>,
        Juergen Gross <jgross@...e.com>,
        Kairui Song <kasong@...hat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Len Brown <len.brown@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Miles Chen <miles.chen@...iatek.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Omar Sandoval <osandov@...com>, Pavel Machek <pavel@....cz>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH RFC 0/6] mm/kdump: allow to exclude pages that are
 logically offline

From: David Hildenbrand
Sent: November 14, 2018 at 11:05:38 PM GMT
> Subject: Re: [PATCH RFC 0/6] mm/kdump: allow to exclude pages that are logically offline
> 
> 
> On 14.11.18 23:57, Nadav Amit wrote:
>> From: David Hildenbrand
>> Sent: November 14, 2018 at 9:16:58 PM GMT
>>> Subject: [PATCH RFC 0/6] mm/kdump: allow to exclude pages that are logically offline
>>> 
>>> 
>>> 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
>>> virtio-balloon and hv-balloon inflated memory will essentially result in
>>> zero pages getting allocated by the hypervisor and the dump getting
>>> filled with this data.
>> 
>> Is there any reason that VMware balloon driver is not mentioned?
> 
> Definitely ...
> 
> ... not ;) . I haven't looked at vmware's balloon driver yet (I only saw
> that there was quite some activity recently). I guess it should have
> similar problems. (I mean reading and dumping data nobody cares about is
> certainly not desired)
> 
> Can you share if something like this is also desired for vmware's
> implementation? (I tagged this as RFC to get some more feedback)
> 
> It should in theory be as simple as adding a handful of
> _SetPageOffline()/_ClearPageOffline() at the right spots.

Thanks, I was just suspecting it is personal ;-)

Actually, some patches that I sent for 4.20 to use the balloon-compaction
infrastructure by the VMware balloon fell between the cracks, and I need
to resend them.

I would obviously prefer that your changes would be done on top of those
that were skipped. This patch-set sounds very reasonable to me, but I prefer
that Julien (cc’d) would also give his opinion.

Regards,
Nadav