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Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capaci
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory |
Date: |
Thu, 30 Jul 2015 11:17:41 +0200 |
On Thu, 30 Jul 2015 10:58:23 +0300
"Michael S. Tsirkin" <address@hidden> wrote:
> On Thu, Jul 30, 2015 at 09:31:34AM +0200, Igor Mammedov wrote:
> > On Thu, 30 Jul 2015 09:29:56 +0300
> > "Michael S. Tsirkin" <address@hidden> wrote:
> >
> > > On Thu, Jul 30, 2015 at 09:25:55AM +0300, Michael S. Tsirkin wrote:
> > > > On Thu, Jul 30, 2015 at 08:22:18AM +0200, Igor Mammedov wrote:
> > > > > On Wed, 29 Jul 2015 18:03:36 +0300
> > > > > "Michael S. Tsirkin" <address@hidden> wrote:
> > > > >
> > > > > > On Wed, Jul 29, 2015 at 01:49:47PM +0200, Igor Mammedov wrote:
> > > > > > > v1->v2:
> > > > > > > * replace probbing with checking for
> > > > > > > /sys/module/vhost/parameters/max_mem_regions and
> > > > > > > if it's missing has non wrong value return
> > > > > > > hardcoded legacy limit (64 slots).
> > > > > > >
> > > > > > > it's defensive patchset which helps to avoid QEMU crashing
> > > > > > > at memory hotplug time by checking that vhost has free capacity
> > > > > > > for an additional memory slot.
> > > > > >
> > > > > > What if vhost is added after memory hotplug? Don't you need
> > > > > > to check that as well?
> > > > > vhost device can be hotplugged after memory hotplug as far as
> > > > > current slots count doesn't exceed its limit,
> > > > > if limit is exceeded device_add would fail or virtio device
> > > > > would fallback to non vhost mode at its start-up (depends on
> > > > > how particular device treats vhost_start failure).
> > > >
> > > > Where exactly does it fail?
> > > > memory_listener_register returns void so clearly it's not that ...
> > >
> > > Oh, dev_start fails. But that's not called at device_add time.
> > > And vhost-user can't fall back to anything.
> > Yes, looks like it would lead to non functional vhost-user backed device
> > since there isn't any error handling at that stage.
> >
> > But it's would be the same without memory hotplug also, one just has to
> > start QEMU with several -name memdev=xxx options to cause that condition.
>
> Absolutely. And kvm has this problem too if using kernels before 2014.
>
> But I have a question: do we have to figure the number of
> chunks exactly? How about being blunt, and just limiting the
> number of memory devices?
it would be guess work, number of chunks is not static and
changes during guest runtime as it configures devices so
chunks # at startup != chunks # at any other time
>
> How about this:
> - teach memory listeners about a new "max mem devices" field
# of mem devices != # of memory ranges
> - when registering a listener, check that # of mem devices
> does not exceed this limit, if not - fail registering
> listener
> - when adding mem device, check no existing listener
> has a limit that conflicts with it
>
> Of course we could add a separate linked list+ register API with just this
> field instead of adding it to a memory listener, if that seems
> more appropriate.
>
>
> > Probably the best place to add this check is at vhost_net_init()
> > so that backend creation fails when one tries to add it on monitor/CLI
>
> I'd say vhost_dev_init - it's not network specific at all.
>
> > >
> > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > Igor Mammedov (2):
> > > > > > > vhost: add vhost_has_free_slot() interface
> > > > > > > pc-dimm: add vhost slots limit check before commiting to hotplug
> > > > > > >
> > > > > > > hw/mem/pc-dimm.c | 7 +++++++
> > > > > > > hw/virtio/vhost-backend.c | 21 ++++++++++++++++++++-
> > > > > > > hw/virtio/vhost-user.c | 8 +++++++-
> > > > > > > hw/virtio/vhost.c | 21 +++++++++++++++++++++
> > > > > > > include/hw/virtio/vhost-backend.h | 2 ++
> > > > > > > include/hw/virtio/vhost.h | 1 +
> > > > > > > stubs/Makefile.objs | 1 +
> > > > > > > stubs/vhost.c | 6 ++++++
> > > > > > > 8 files changed, 65 insertions(+), 2 deletions(-)
> > > > > > > create mode 100644 stubs/vhost.c
> > > > > > >
> > > > > > > --
> > > > > > > 1.8.3.1
> > >
>
- Re: [Qemu-devel] [PATCH for-2.4 v2 1/2] vhost: add vhost_has_free_slot() interface, (continued)
Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory, Michael S. Tsirkin, 2015/07/29
- Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory, Igor Mammedov, 2015/07/30
- Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory, Michael S. Tsirkin, 2015/07/30
- Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory, Michael S. Tsirkin, 2015/07/30
- Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory, Igor Mammedov, 2015/07/30
- Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory, Michael S. Tsirkin, 2015/07/30
- Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory,
Igor Mammedov <=
- Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory, Michael S. Tsirkin, 2015/07/30
- Re: [Qemu-devel] [PATCH for-2.4 v2 0/2] vhost: check if vhost has capacity for hotplugged memory, Igor Mammedov, 2015/07/31