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From: David Hildenbrand <david@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>,
	Alexander Duyck <alexander.duyck@gmail.com>
Cc: 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>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>
Subject: Re: use of shrinker in virtio balloon free page hinting
Date: Wed, 17 Jul 2019 16:10:47 +0200
Message-ID: <959237f9-22cc-1e57-e07d-b8dc3ddf9ed6@redhat.com> (raw)
In-Reply-To: <20190717071332-mutt-send-email-mst@kernel.org>

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

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

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.



David / dhildenb

  parent reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-17 11:20 Michael S. Tsirkin
2019-07-17 11:32 ` David Hildenbrand
2019-07-17 14:10 ` David Hildenbrand [this message]
2019-07-17 14:34   ` Michael S. Tsirkin
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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