From: "Michael S. Tsirkin" <mst@redhat.com>
To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Peter Xu <peterx@redhat.com>, Wei Wang <wei.w.wang@intel.com>,
qemu-devel@nongnu.org, virtio-dev@lists.oasis-open.org,
quintela@redhat.com, yang.zhang.wz@gmail.com, quan.xu0@gmail.com,
liliang.opensource@gmail.com, pbonzini@redhat.com,
nilal@redhat.com
Subject: Re: [Qemu-devel] [PATCH v7 0/5] virtio-balloon: free page hint reporting support
Date: Tue, 5 Jun 2018 17:39:34 +0300 [thread overview]
Message-ID: <20180605173342-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20180601153328.GC2531@work-vm>
On Fri, Jun 01, 2018 at 04:33:29PM +0100, Dr. David Alan Gilbert wrote:
> I think the answer is no - it doesn't matter; by telling the hypervisor
> the page is 'free' the kernel gives freedom to the hypervisor to
> discard the page contents.
I'd like to call attention to this since it's easy to get confused.
That's not exactly true in the current interface.
It's a *hint* not a guarantee.
Let me explain.
It all starts with a request from hypervisor and each free page report
is matched to a request. What the report says is that the page was free
*sometime after the request was sent to guest*. If hypervisor was
tracking changes to page all the time since before sending the request,
it can conclude that page was free and can discard the contents. If it
wasn't then it can't be sure and can not discard the page, it can maybe
use the hint for other decisions (e.g. unused => should be sent before
other pages).
--
MST
prev parent reply other threads:[~2018-06-05 14:39 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-24 6:13 [Qemu-devel] [PATCH v7 0/5] virtio-balloon: free page hint reporting support Wei Wang
2018-04-24 6:13 ` [Qemu-devel] [PATCH v7 1/5] bitmap: bitmap_count_one_with_offset Wei Wang
2018-04-24 6:13 ` [Qemu-devel] [PATCH v7 2/5] migration: use bitmap_mutex in migration_bitmap_clear_dirty Wei Wang
2018-06-01 3:37 ` Peter Xu
2018-04-24 6:13 ` [Qemu-devel] [PATCH v7 3/5] migration: API to clear bits of guest free pages from the dirty bitmap Wei Wang
2018-06-01 4:00 ` Peter Xu
2018-06-01 7:36 ` Wei Wang
2018-06-01 10:06 ` Peter Xu
2018-06-01 12:32 ` Wei Wang
2018-06-04 2:49 ` Peter Xu
2018-06-04 7:43 ` Wei Wang
2018-04-24 6:13 ` [Qemu-devel] [PATCH v7 4/5] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT Wei Wang
2018-05-29 15:24 ` Michael S. Tsirkin
2018-05-30 9:12 ` Wei Wang
2018-05-30 12:47 ` Michael S. Tsirkin
2018-05-31 2:27 ` Wei Wang
2018-05-31 17:42 ` Michael S. Tsirkin
2018-06-01 3:18 ` Wei Wang
2018-06-04 8:04 ` Wei Wang
2018-06-05 6:58 ` Peter Xu
2018-06-05 13:22 ` Wei Wang
2018-06-06 5:42 ` Peter Xu
2018-06-06 10:04 ` Wei Wang
2018-06-06 11:02 ` Peter Xu
2018-06-07 5:24 ` Wei Wang
2018-06-07 6:32 ` Peter Xu
2018-06-07 11:59 ` Wei Wang
2018-06-08 2:17 ` Peter Xu
2018-06-08 7:14 ` Wei Wang
2018-06-08 7:31 ` Wei Wang
2018-06-06 6:43 ` Peter Xu
2018-06-06 10:11 ` Wei Wang
2018-06-07 3:17 ` Peter Xu
2018-06-07 5:29 ` Wei Wang
2018-06-07 6:58 ` Peter Xu
2018-06-07 12:01 ` Wei Wang
2018-06-08 1:37 ` Peter Xu
2018-06-08 1:58 ` Peter Xu
2018-06-08 1:58 ` Michael S. Tsirkin
2018-06-08 2:34 ` Peter Xu
2018-06-08 2:49 ` Michael S. Tsirkin
2018-06-08 3:34 ` Peter Xu
2018-04-24 6:13 ` [Qemu-devel] [PATCH v7 5/5] migration: use the free page hint feature from balloon Wei Wang
2018-04-24 6:42 ` [Qemu-devel] [PATCH v7 0/5] virtio-balloon: free page hint reporting support Wei Wang
2018-05-14 1:22 ` Wei Wang
2018-05-29 15:00 ` Hailiang Zhang
2018-05-29 15:24 ` Michael S. Tsirkin
2018-06-01 4:58 ` Peter Xu
2018-06-01 5:07 ` Peter Xu
2018-06-01 7:29 ` Wei Wang
2018-06-01 10:02 ` Peter Xu
2018-06-01 12:31 ` Wei Wang
2018-06-01 7:21 ` Wei Wang
2018-06-01 10:40 ` Peter Xu
2018-06-01 15:33 ` Dr. David Alan Gilbert
2018-06-05 6:42 ` Peter Xu
2018-06-05 14:40 ` Michael S. Tsirkin
2018-06-05 14:39 ` Michael S. Tsirkin [this message]
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