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Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks
From: |
Michal Hocko |
Subject: |
Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks |
Date: |
Tue, 25 Jul 2017 13:25:13 +0200 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Tue 25-07-17 17:32:00, Wei Wang wrote:
> On 07/24/2017 05:00 PM, Michal Hocko wrote:
> >On Wed 19-07-17 20:01:18, Wei Wang wrote:
> >>On 07/19/2017 04:13 PM, Michal Hocko wrote:
> >[...
> >>>All you should need is the check for the page reference count, no? I
> >>>assume you do some sort of pfn walk and so you should be able to get an
> >>>access to the struct page.
> >>Not necessarily - the guest struct page is not seen by the hypervisor. The
> >>hypervisor only gets those guest pfns which are hinted as unused. From the
> >>hypervisor (host) point of view, a guest physical address corresponds to a
> >>virtual address of a host process. So, once the hypervisor knows a guest
> >>physical page is unsued, it knows that the corresponding virtual memory of
> >>the process doesn't need to be transferred in the 1st round.
> >I am sorry, but I do not understand. Why cannot _guest_ simply check the
> >struct page ref count and send them to the hypervisor?
>
> Were you suggesting the following?
> 1) get a free page block from the page list using the API;
No. Use a pfn walk, check the reference count and skip those pages which
have 0 ref count. I suspected that you need to do some sort of the pfn
walk anyway because you somehow have to evaluate a memory to migrate,
right?
> 2) if page->ref_count == 0, send it to the hypervisor
yes
> Btw, ref_count may also change at any time.
>
> >Is there any
> >documentation which describes the workflow or code which would use your
> >new API?
> >
>
> It's used in the balloon driver (patch 8). We don't have any docs yet, but
> I think the high level workflow is the two steps above.
I will have a look.
--
Michal Hocko
SUSE Labs
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, (continued)
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Michal Hocko, 2017/07/14
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Michael S. Tsirkin, 2017/07/14
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Michal Hocko, 2017/07/17
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Wei Wang, 2017/07/17
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Michal Hocko, 2017/07/19
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Wei Wang, 2017/07/19
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Michal Hocko, 2017/07/24
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Wei Wang, 2017/07/25
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks,
Michal Hocko <=
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Wei Wang, 2017/07/25
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Michal Hocko, 2017/07/25
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Wang, Wei W, 2017/07/25
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Michal Hocko, 2017/07/25
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Wei Wang, 2017/07/25
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Michal Hocko, 2017/07/26
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Wei Wang, 2017/07/26
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Michal Hocko, 2017/07/26
- Re: [Qemu-devel] [PATCH v12 6/8] mm: support reporting free page blocks, Wang, Wei W, 2017/07/26
[Qemu-devel] [PATCH v12 5/8] virtio-balloon: VIRTIO_BALLOON_F_SG, Wei Wang, 2017/07/12