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From: Jason Wang <jasowang@redhat.com>
Date: Thu, 25 Apr 2024 09:35:58 +0800
Message-ID: <CACGkMEtosWhV-eJbPetgPtp-Thg31CLUBGaENbQRknYtzEV3bQ@mail.gmail.com>
Subject: Re: [PATCH v5 3/5] vduse: Add function to get/free the pages for reconnection
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Cindy Lu <lulu@redhat.com>, linux-kernel@vger.kernel.org, 
	virtualization@lists.linux-foundation.org
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On Wed, Apr 24, 2024 at 5:51=E2=80=AFPM Michael S. Tsirkin <mst@redhat.com>=
 wrote:
>
> On Wed, Apr 24, 2024 at 08:44:10AM +0800, Jason Wang wrote:
> > On Tue, Apr 23, 2024 at 4:42=E2=80=AFPM Michael S. Tsirkin <mst@redhat.=
com> wrote:
> > >
> > > On Tue, Apr 23, 2024 at 11:09:59AM +0800, Jason Wang wrote:
> > > > On Tue, Apr 23, 2024 at 4:05=E2=80=AFAM Michael S. Tsirkin <mst@red=
hat.com> wrote:
> > > > >
> > > > > On Thu, Apr 18, 2024 at 08:57:51AM +0800, Jason Wang wrote:
> > > > > > On Wed, Apr 17, 2024 at 5:29=E2=80=AFPM Michael S. Tsirkin <mst=
@redhat.com> wrote:
> > > > > > >
> > > > > > > On Fri, Apr 12, 2024 at 09:28:23PM +0800, Cindy Lu wrote:
> > > > > > > > Add the function vduse_alloc_reconnnect_info_mem
> > > > > > > > and vduse_alloc_reconnnect_info_mem
> > > > > > > > These functions allow vduse to allocate and free memory for=
 reconnection
> > > > > > > > information. The amount of memory allocated is vq_num pages=
.
> > > > > > > > Each VQS will map its own page where the reconnection infor=
mation will be saved
> > > > > > > >
> > > > > > > > Signed-off-by: Cindy Lu <lulu@redhat.com>
> > > > > > > > ---
> > > > > > > >  drivers/vdpa/vdpa_user/vduse_dev.c | 40 ++++++++++++++++++=
++++++++++++
> > > > > > > >  1 file changed, 40 insertions(+)
> > > > > > > >
> > > > > > > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/v=
dpa/vdpa_user/vduse_dev.c
> > > > > > > > index ef3c9681941e..2da659d5f4a8 100644
> > > > > > > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > > > > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > > > > > > @@ -65,6 +65,7 @@ struct vduse_virtqueue {
> > > > > > > >       int irq_effective_cpu;
> > > > > > > >       struct cpumask irq_affinity;
> > > > > > > >       struct kobject kobj;
> > > > > > > > +     unsigned long vdpa_reconnect_vaddr;
> > > > > > > >  };
> > > > > > > >
> > > > > > > >  struct vduse_dev;
> > > > > > > > @@ -1105,6 +1106,38 @@ static void vduse_vq_update_effectiv=
e_cpu(struct vduse_virtqueue *vq)
> > > > > > > >
> > > > > > > >       vq->irq_effective_cpu =3D curr_cpu;
> > > > > > > >  }
> > > > > > > > +static int vduse_alloc_reconnnect_info_mem(struct vduse_de=
v *dev)
> > > > > > > > +{
> > > > > > > > +     unsigned long vaddr =3D 0;
> > > > > > > > +     struct vduse_virtqueue *vq;
> > > > > > > > +
> > > > > > > > +     for (int i =3D 0; i < dev->vq_num; i++) {
> > > > > > > > +             /*page 0~ vq_num save the reconnect info for =
vq*/
> > > > > > > > +             vq =3D dev->vqs[i];
> > > > > > > > +             vaddr =3D get_zeroed_page(GFP_KERNEL);
> > > > > > >
> > > > > > >
> > > > > > > I don't get why you insist on stealing kernel memory for some=
thing
> > > > > > > that is just used by userspace to store data for its own use.
> > > > > > > Userspace does not lack ways to persist data, for example,
> > > > > > > create a regular file anywhere in the filesystem.
> > > > > >
> > > > > > Good point. So the motivation here is to:
> > > > > >
> > > > > > 1) be self contained, no dependency for high speed persist data
> > > > > > storage like tmpfs
> > > > >
> > > > > No idea what this means.
> > > >
> > > > I mean a regular file may slow down the datapath performance, so
> > > > usually the application will try to use tmpfs and other which is a
> > > > dependency for implementing the reconnection.
> > >
> > > Are we worried about systems without tmpfs now?
> >
> > Yes.
>
> Why? Who ships these?

Not sure, but it could be disabled or unmounted. I'm not sure make
VDUSE depends on TMPFS is a good idea.

Thanks