From: "Kasireddy, Vivek" <vivek.kasireddy@intel.com>
To: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
Alistair Popple <apopple@nvidia.com>,
Gerd Hoffmann <kraxel@redhat.com>,
"Kim, Dongwon" <dongwon.kim@intel.com>,
David Hildenbrand <david@redhat.com>,
"Chang, Junxiao" <junxiao.chang@intel.com>,
Peter Xu <peterx@redhat.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
Mike Kravetz <mike.kravetz@oracle.com>
Subject: RE: [RFC v1 1/3] mm/mmu_notifier: Add a new notifier for mapping updates (new pages)
Date: Tue, 25 Jul 2023 22:24:21 +0000 [thread overview]
Message-ID: <CH3PR11MB71777432A63D3FAAE7E70F22F803A@CH3PR11MB7177.namprd11.prod.outlook.com> (raw)
In-Reply-To: <75e3a74a-68f5-df-9a49-a0553c04320@google.com>
Hi Hugh,
>
> On Mon, 24 Jul 2023, Kasireddy, Vivek wrote:
> > Hi Jason,
> > > On Mon, Jul 24, 2023 at 07:54:38AM +0000, Kasireddy, Vivek wrote:
> > >
> > > > > I'm not at all familiar with the udmabuf use case but that sounds
> > > > > brittle and effectively makes this notifier udmabuf specific right?
> > > > Oh, Qemu uses the udmabuf driver to provide Host Graphics
> components
> > > > (such as Spice, Gstreamer, UI, etc) zero-copy access to Guest created
> > > > buffers. In other words, from a core mm standpoint, udmabuf just
> > > > collects a bunch of pages (associated with buffers) scattered inside
> > > > the memfd (Guest ram backed by shmem or hugetlbfs) and wraps
> > > > them in a dmabuf fd. And, since we provide zero-copy access, we
> > > > use DMA fences to ensure that the components on the Host and
> > > > Guest do not access the buffer simultaneously.
> > >
> > > So why do you need to track updates proactively like this?
> > As David noted in the earlier series, if Qemu punches a hole in its memfd
> > that goes through pages that are registered against a udmabuf fd, then
> > udmabuf needs to update its list with new pages when the hole gets
> > filled after (guest) writes. Otherwise, we'd run into the coherency
> > problem (between udmabuf and memfd) as demonstrated in the selftest
> > (patch #3 in this series).
>
> Wouldn't this all be very much better if Qemu stopped punching holes there?
I think holes can be punched anywhere in the memfd for various reasons. Some
of the use-cases where this would be done were identified by David. Here is what
he said in an earlier discussion:
"There are *probably* more issues on the QEMU side when udmabuf is paired
with things like MADV_DONTNEED/FALLOC_FL_PUNCH_HOLE used for
virtio-balloon, virtio-mem, postcopy live migration, ... for example, in"
Thanks,
Vivek
>
> Hugh
next prev parent reply other threads:[~2023-07-25 22:25 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-18 8:28 [RFC v1 0/3] udmabuf: Replace pages when there is FALLOC_FL_PUNCH_HOLE in memfd Vivek Kasireddy
2023-07-18 8:28 ` [RFC v1 1/3] mm/mmu_notifier: Add a new notifier for mapping updates (new pages) Vivek Kasireddy
2023-07-18 15:36 ` Jason Gunthorpe
2023-07-19 0:05 ` Kasireddy, Vivek
2023-07-19 0:24 ` Jason Gunthorpe
2023-07-19 6:19 ` Kasireddy, Vivek
2023-07-19 2:08 ` Alistair Popple
2023-07-20 7:43 ` Kasireddy, Vivek
2023-07-20 9:00 ` Alistair Popple
2023-07-24 7:54 ` Kasireddy, Vivek
2023-07-24 13:35 ` Jason Gunthorpe
2023-07-24 20:32 ` Kasireddy, Vivek
2023-07-25 4:30 ` Hugh Dickins
2023-07-25 22:24 ` Kasireddy, Vivek [this message]
2023-07-27 21:43 ` Peter Xu
2023-07-29 0:08 ` Kasireddy, Vivek
2023-07-31 17:05 ` Peter Xu
2023-08-01 7:11 ` Kasireddy, Vivek
2023-08-01 21:57 ` Peter Xu
2023-08-03 8:08 ` Kasireddy, Vivek
2023-08-03 13:02 ` Peter Xu
2023-07-25 12:36 ` Jason Gunthorpe
2023-07-25 22:44 ` Kasireddy, Vivek
2023-07-25 22:53 ` Jason Gunthorpe
2023-07-27 7:34 ` Kasireddy, Vivek
2023-07-27 11:58 ` Jason Gunthorpe
2023-07-29 0:46 ` Kasireddy, Vivek
2023-07-30 23:09 ` Jason Gunthorpe
2023-08-01 5:32 ` Kasireddy, Vivek
2023-08-01 12:19 ` Jason Gunthorpe
2023-08-01 12:22 ` David Hildenbrand
2023-08-01 12:23 ` Jason Gunthorpe
2023-08-01 12:26 ` David Hildenbrand
2023-08-01 12:26 ` Jason Gunthorpe
2023-08-01 12:28 ` David Hildenbrand
2023-08-01 17:53 ` Kasireddy, Vivek
2023-08-01 18:19 ` Jason Gunthorpe
2023-08-03 7:35 ` Kasireddy, Vivek
2023-08-03 12:14 ` Jason Gunthorpe
2023-08-03 12:32 ` David Hildenbrand
2023-08-04 0:14 ` Alistair Popple
2023-08-04 6:39 ` Kasireddy, Vivek
2023-08-04 7:23 ` David Hildenbrand
2023-08-04 21:53 ` Kasireddy, Vivek
2023-08-04 12:49 ` Jason Gunthorpe
2023-08-08 7:37 ` Kasireddy, Vivek
2023-08-08 12:42 ` Jason Gunthorpe
2023-08-16 6:43 ` Kasireddy, Vivek
2023-08-21 9:02 ` Alistair Popple
2023-08-22 6:14 ` Kasireddy, Vivek
2023-08-22 8:15 ` Alistair Popple
2023-08-24 6:48 ` Kasireddy, Vivek
2023-08-28 4:38 ` Kasireddy, Vivek
2023-08-30 16:02 ` Jason Gunthorpe
2023-07-25 3:38 ` Alistair Popple
2023-07-24 13:36 ` Alistair Popple
2023-07-24 13:37 ` Jason Gunthorpe
2023-07-24 20:42 ` Kasireddy, Vivek
2023-07-25 3:14 ` Alistair Popple
2023-07-18 8:28 ` [RFC v1 2/3] udmabuf: Replace pages when there is FALLOC_FL_PUNCH_HOLE in memfd Vivek Kasireddy
2023-08-02 12:40 ` Daniel Vetter
2023-08-03 8:24 ` Kasireddy, Vivek
2023-08-03 8:32 ` Daniel Vetter
2023-07-18 8:28 ` [RFC v1 3/3] selftests/dma-buf/udmabuf: Add tests for huge pages and FALLOC_FL_PUNCH_HOLE Vivek Kasireddy
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CH3PR11MB71777432A63D3FAAE7E70F22F803A@CH3PR11MB7177.namprd11.prod.outlook.com \
--to=vivek.kasireddy@intel.com \
--cc=apopple@nvidia.com \
--cc=david@redhat.com \
--cc=dongwon.kim@intel.com \
--cc=dri-devel@lists.freedesktop.org \
--cc=hughd@google.com \
--cc=jgg@nvidia.com \
--cc=junxiao.chang@intel.com \
--cc=kraxel@redhat.com \
--cc=linux-mm@kvack.org \
--cc=mike.kravetz@oracle.com \
--cc=peterx@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).