From: David Hildenbrand <david@redhat.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
Rik van Riel <riel@redhat.com>,
Dave Hansen <dave.hansen@intel.com>,
Wei Wang <wei.w.wang@intel.com>,
linux-kernel@vger.kernel.org, qemu-devel@nongnu.org,
virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
linux-mm@kvack.org, mst@redhat.com, cornelia.huck@de.ibm.com,
akpm@linux-foundation.org, mgorman@techsingularity.net,
aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com,
liliang.opensource@gmail.com
Cc: Nitesh Narayan Lal <nilal@redhat.com>
Subject: Re: [PATCH v11 4/6] mm: function to offer a page block on the free list
Date: Wed, 21 Jun 2017 15:47:15 +0200 [thread overview]
Message-ID: <a4f68630-c143-2579-8999-b1506bc6e272@redhat.com> (raw)
In-Reply-To: <c5f8cf53-c30b-a7ec-a8e8-9a2c120bdff6@de.ibm.com>
On 21.06.2017 14:56, Christian Borntraeger wrote:
> On 06/20/2017 06:49 PM, David Hildenbrand wrote:
>> On 20.06.2017 18:44, Rik van Riel wrote:
>>> On Mon, 2017-06-12 at 07:10 -0700, Dave Hansen wrote:
>>>
>>>> The hypervisor is going to throw away the contents of these pages,
>>>> right? As soon as the spinlock is released, someone can allocate a
>>>> page, and put good data in it. What keeps the hypervisor from
>>>> throwing
>>>> away good data?
>>>
>>> That looks like it may be the wrong API, then?
>>>
>>> We already have hooks called arch_free_page and
>>> arch_alloc_page in the VM, which are called when
>>> pages are freed, and allocated, respectively.
>>>
>>> Nitesh Lal (on the CC list) is working on a way
>>> to efficiently batch recently freed pages for
>>> free page hinting to the hypervisor.
>>>
>>> If that is done efficiently enough (eg. with
>>> MADV_FREE on the hypervisor side for lazy freeing,
>>> and lazy later re-use of the pages), do we still
>>> need the harder to use batch interface from this
>>> patch?
>>>
>> David's opinion incoming:
>>
>> No, I think proper free page hinting would be the optimum solution, if
>> done right. This would avoid the batch interface and even turn
>> virtio-balloon in some sense useless.
>>
I said "some sense" for a reason. Mainly because other techniques are
being worked on that are to fill the holes.
> Two reasons why I disagree:
> - virtio-balloon is often used as memory hotplug. (e.g. libvirts current/max memory
> uses virtio ballon)
I know, while one can argue if this real unplug as there are basically
no guarantees (see virtio-mem RFC) it is used by people because there is
simply no alternative. Still, for now some people use it for that.
> - free page hinting will not allow to shrink the page cache of guests (like a ballooner does)
There are currently some projects ongoing that try to avoid the page
cache in the guest completely.
--
Thanks,
David
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next prev parent reply other threads:[~2017-06-21 13:47 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-09 10:41 [PATCH v11 0/6] Virtio-balloon Enhancement Wei Wang
2017-06-09 10:41 ` [PATCH v11 1/6] virtio-balloon: deflate via a page list Wei Wang
2017-06-09 10:41 ` [PATCH v11 2/6] virtio-balloon: coding format cleanup Wei Wang
2017-06-09 10:41 ` [PATCH v11 3/6] virtio-balloon: VIRTIO_BALLOON_F_PAGE_CHUNKS Wei Wang
2017-06-13 17:56 ` Michael S. Tsirkin
2017-06-13 17:59 ` Dave Hansen
2017-06-13 18:55 ` Michael S. Tsirkin
2017-06-15 8:10 ` [virtio-dev] " Wei Wang
2017-06-16 3:19 ` Michael S. Tsirkin
2017-06-28 15:04 ` Matthew Wilcox
2017-07-12 13:05 ` Wei Wang
2017-06-09 10:41 ` [PATCH v11 4/6] mm: function to offer a page block on the free list Wei Wang
2017-06-12 14:10 ` Dave Hansen
2017-06-12 16:28 ` Michael S. Tsirkin
2017-06-12 16:42 ` Dave Hansen
2017-06-12 20:34 ` Michael S. Tsirkin
2017-06-12 20:54 ` Dave Hansen
2017-06-13 2:56 ` Wei Wang
2017-06-20 16:44 ` Rik van Riel
2017-06-20 16:49 ` David Hildenbrand
2017-06-20 17:29 ` Rik van Riel
2017-06-20 18:26 ` Michael S. Tsirkin
2017-06-20 19:51 ` Rik van Riel
2017-06-21 12:41 ` Michael S. Tsirkin
2017-06-21 8:38 ` [Qemu-devel] " Wei Wang
2017-06-20 18:17 ` Michael S. Tsirkin
2017-06-20 18:54 ` David Hildenbrand
2017-06-20 18:56 ` Michael S. Tsirkin
2017-06-20 19:01 ` David Hildenbrand
2017-06-21 12:56 ` Christian Borntraeger
2017-06-21 13:47 ` David Hildenbrand [this message]
2017-06-09 10:41 ` [PATCH v11 5/6] mm: export symbol of next_zone and first_online_pgdat Wei Wang
2017-06-09 10:41 ` [PATCH v11 6/6] virtio-balloon: VIRTIO_BALLOON_F_CMD_VQ Wei Wang
2017-06-12 14:07 ` Dave Hansen
2017-06-13 10:17 ` Wei Wang
2017-06-20 16:18 ` Michael S. Tsirkin
2017-06-21 3:28 ` [virtio-dev] " Wei Wang
2017-06-21 12:28 ` Michael S. Tsirkin
2017-06-22 8:40 ` Wei Wang
2017-06-28 15:01 ` Michael S. Tsirkin
2017-07-12 12:57 ` Wei Wang
2017-06-09 11:18 ` [PATCH v11 0/6] Virtio-balloon Enhancement Wang, Wei W
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