From: "Michael S. Tsirkin" <mst@redhat.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
virtualization@lists.linux-foundation.org,
Tyler Sanderson <tysand@google.com>,
Wei Wang <wei.w.wang@intel.com>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>,
David Rientjes <rientjes@google.com>,
Nadav Amit <namit@vmware.com>, Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH v1 3/3] virtio-balloon: Switch back to OOM handler for VIRTIO_BALLOON_F_DEFLATE_ON_OOM
Date: Thu, 6 Feb 2020 04:09:38 -0500 [thread overview]
Message-ID: <20200206040927-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <a5dc8a7c-7384-5efa-e251-1cd9a240e73a@redhat.com>
On Thu, Feb 06, 2020 at 10:05:43AM +0100, David Hildenbrand wrote:
> >> commit bf50e69f63d21091e525185c3ae761412be0ba72
> >> Author: Dave Hansen <dave@linux.vnet.ibm.com>
> >> Date: Thu Apr 7 10:43:25 2011 -0700
> >>
> >> virtio balloon: kill tell-host-first logic
> >>
> >> The virtio balloon driver has a VIRTIO_BALLOON_F_MUST_TELL_HOST
> >> feature bit. Whenever the bit is set, the guest kernel must
> >> always tell the host before we free pages back to the allocator.
> >> Without this feature, we might free a page (and have another
> >> user touch it) while the hypervisor is unprepared for it.
> >>
> >> But, if the bit is _not_ set, we are under no obligation to
> >> reverse the order; we're under no obligation to do _anything_.
> >> As of now, qemu-kvm defines the bit, but doesn't set it.
> >
> > Well this is not what the spec says in the end.
>
> I didn't check the spec, maybe I should do that :)
>
> > To continue that commit message:
> >
> > This patch makes the "tell host first" logic the only case. This
> > should make everybody happy, and reduce the amount of untested or
> > untestable code in the kernel.
>
> Yeah, but this comment explains that the current deflate is only in
> place, because it makes the code simpler (to support both cases). Of
> course, doing the deflate might result in performance improvements.
> (e.g., MADV_WILLNEED)
>
> >
> > you can try proposing the change to the virtio TC, see what do others
> > think.
>
> We can just drop the comment from this patch for now. The tell_host host
> not be an issue AFAIKS.
I guess it's a good idea.
> --
> Thanks,
>
> David / dhildenb
next prev parent reply other threads:[~2020-02-06 9:09 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-05 16:33 [PATCH v1 0/3] virtio-balloon: Fixes + switch back to OOM handler David Hildenbrand
2020-02-05 16:34 ` [PATCH v1 1/3] virtio-balloon: Fix memory leak when unloading while hinting is in progress David Hildenbrand
2020-02-06 8:36 ` Michael S. Tsirkin
2020-02-05 16:34 ` [PATCH v1 2/3] virtio_balloon: Fix memory leaks on errors in virtballoon_probe() David Hildenbrand
2020-02-06 8:36 ` Michael S. Tsirkin
2020-02-05 16:34 ` [PATCH v1 3/3] virtio-balloon: Switch back to OOM handler for VIRTIO_BALLOON_F_DEFLATE_ON_OOM David Hildenbrand
2020-02-05 22:37 ` Tyler Sanderson
2020-02-05 22:52 ` David Hildenbrand
2020-02-05 23:06 ` Tyler Sanderson
2020-02-06 7:40 ` Michael S. Tsirkin
2020-02-06 8:42 ` David Hildenbrand
2020-02-06 8:57 ` Michael S. Tsirkin
2020-02-06 9:05 ` David Hildenbrand
2020-02-06 9:09 ` Michael S. Tsirkin [this message]
2020-02-06 8:57 ` Wang, Wei W
2020-02-06 9:11 ` Michael S. Tsirkin
2020-02-06 9:12 ` Michael S. Tsirkin
2020-02-06 9:21 ` David Hildenbrand
2020-02-14 9:51 ` David Hildenbrand
2020-02-14 13:31 ` Wang, Wei W
2020-02-16 9:47 ` Michael S. Tsirkin
2020-02-21 3:29 ` Tyler Sanderson
2020-03-08 4:47 ` Tyler Sanderson
2020-03-09 9:03 ` David Hildenbrand
2020-03-09 10:14 ` Michael S. Tsirkin
2020-03-09 10:59 ` David Hildenbrand
2020-03-09 10:24 ` Michael S. Tsirkin
2020-02-14 14:06 ` Michal Hocko
2020-02-14 14:18 ` David Hildenbrand
2020-02-14 20:48 ` Tyler Sanderson
2020-02-14 21:17 ` David Hildenbrand
2020-02-16 9:46 ` Michael S. Tsirkin
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