From: "Michael S. Tsirkin" <mst@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
wei.w.wang@intel.com, Nitesh Narayan Lal <nitesh@redhat.com>,
kvm list <kvm@vger.kernel.org>,
Dave Hansen <dave.hansen@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Yang Zhang <yang.zhang.wz@gmail.com>,
pagupta@redhat.com, Rik van Riel <riel@surriel.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
lcapitulino@redhat.com, Andrea Arcangeli <aarcange@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
dan.j.williams@intel.com,
Alexander Duyck <alexander.h.duyck@linux.intel.com>
Subject: Re: use of shrinker in virtio balloon free page hinting
Date: Wed, 17 Jul 2019 10:34:15 -0400 [thread overview]
Message-ID: <20190717103208-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <959237f9-22cc-1e57-e07d-b8dc3ddf9ed6@redhat.com>
On Wed, Jul 17, 2019 at 04:10:47PM +0200, David Hildenbrand wrote:
> On 17.07.19 13:20, Michael S. Tsirkin wrote:
> > Wei, others,
> >
> > ATM virtio_balloon_shrinker_scan will only get registered
> > when deflate on oom feature bit is set.
> >
> > Not sure whether that's intentional. Assuming it is:
> >
> > virtio_balloon_shrinker_scan will try to locate and free
> > pages that are processed by host.
> > The above seems broken in several ways:
> > - count ignores the free page list completely
> > - if free pages are being reported, pages freed
> > by shrinker will just get re-allocated again
>
> Trying to answer your questions (not sure if I fully understood what you
> mean)
>
> virtio_balloon_shrinker_scan() will not be called due to inflation
> requests (balloon_page_alloc()). It will be called whenever the system
> is OOM, e.g., when starting a new application.
>
> I assume you were expecting the shrinker getting called due to
> balloon_page_alloc(). however, that is not the case as we pass
> "__GFP_NORETRY".
Right but it's possible we exhaust all memory, then
someone else asks for a single page and that invokes
the shrinker.
>
> To test, something like:
>
> 1. Start a VM with
>
> -device virtio-balloon-pci,deflate-on-oom=true
>
> 2. Inflate the balloon, e.g.,
>
> QMP: balloon 1024
> QMP: info balloon
> -> 1024
>
> See how "MemTotal" in /proc/meminfo in the guest won't change
>
> 3. Run a workload that exhausts memory in the guest (OOM).
>
> See how the balloon was automatically deflated
>
> QMP: info balloon
> -> Something bigger than 1024
>
>
> Not sure if it is broken, last time I played with it, it worked, but
> that was ~1-2 years ago.
>
> --
>
> Thanks,
>
> David / dhildenb
Sorry I was unclear. The question was about
VIRTIO_BALLOON_F_FREE_PAGE_HINT specifically.
--
MST
next prev parent reply other threads:[~2019-07-17 14:34 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-17 11:20 use of shrinker in virtio balloon free page hinting Michael S. Tsirkin
2019-07-17 11:32 ` David Hildenbrand
2019-07-17 14:10 ` David Hildenbrand
2019-07-17 14:34 ` Michael S. Tsirkin [this message]
2019-07-17 14:38 ` David Hildenbrand
2019-07-17 15:46 ` Wang, Wei W
2019-07-18 4:13 ` Michael S. Tsirkin
2019-07-18 5:57 ` Wei Wang
2019-07-18 5:58 ` Michael S. Tsirkin
2019-07-18 6:30 ` Wei Wang
2019-07-18 6:47 ` Michael S. Tsirkin
2019-07-18 9:08 ` Wei Wang
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