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Re: [Qemu-devel] [PATCH] set VIRTIO_BALLOON_F_MUST_TELL_HOST uncondition
From: |
Dave Hansen |
Subject: |
Re: [Qemu-devel] [PATCH] set VIRTIO_BALLOON_F_MUST_TELL_HOST unconditionally |
Date: |
Mon, 18 Apr 2011 08:37:14 -0700 |
On Fri, 2011-04-15 at 14:20 -0500, Anthony Liguori wrote:
> On 04/15/2011 02:15 PM, Dave Hansen wrote:
> > On Fri, 2011-04-15 at 12:17 -0500, Anthony Liguori wrote:
> >> If you're in OOM and you need memory, you can't ask the host for more
> >> and wait for a response. You have to reclaim it immediately.
> > Why not? The call in to the notifier chain the s390 case is
> > synchronous. The OOM only affects one task at a time and won't proceed
> > elsewhere while this is going on.
>
> Because if we tell the host, we have to wait for the host to ack which
> means we'd sleep waiting for an interrupt. Can you do this in the OOM path?
Sure. One of the s390 handlers sleeps today.
> > Why do we even _tell_ qemu, though? The MADV_WILLNEED is nice, but far
> > from being necessary. We could just skip the entire notification in OOM
> > situations.
>
> There's really no particular reason to other than symmetry.
When we get there, it sounds like we can simply _skip_ the notification
in the qemu case.
-- Dave