From: Roman Kagan <rkagan@virtuozzo.com>
To: "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>
Cc: "jasowang@redhat.com" <jasowang@redhat.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"vkuznets@redhat.com" <vkuznets@redhat.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"mst@redhat.com" <mst@redhat.com>
Subject: Re: [PATCH v2 0/3] exclude hyperv synic sections from vhost
Date: Wed, 15 Jan 2020 12:12:59 +0000 [thread overview]
Message-ID: <20200115121256.GA33252@rkaganb.sw.ru> (raw)
In-Reply-To: <20200113173647.84842-1-dgilbert@redhat.com>
On Mon, Jan 13, 2020 at 05:36:44PM +0000, Dr. David Alan Gilbert (git) wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>
> Hyperv's synic (that we emulate) is a feature that allows the guest
> to place some magic (4k) pages of RAM anywhere it likes in GPA.
> This confuses vhost's RAM section merging when these pages
> land over the top of hugepages.
>
> Since they're not normal RAM, and they shouldn't have vhost DMAing
> into them, exclude them from the vhost set.
I still don't think this is correct assessment. These pages are normal
RAM, perfectly eligible for DMA and what not.
It was a thinko to implement them this way, taking the Hyper-V spec too
literally. Among the downsides is the excessive consumption of KVM
memslots, and unnecessary large page splits or conflicts with
unsplittable ones. I'm working on an alternative approach that doesn't
suffer from these issues; struggling to preserve compatibility ATM.
Thanks,
Roman.
prev parent reply other threads:[~2020-01-15 12:13 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-13 17:36 [PATCH v2 0/3] exclude hyperv synic sections from vhost Dr. David Alan Gilbert (git)
2020-01-13 17:36 ` [PATCH v2 1/3] vhost: Add names to section rounded warning Dr. David Alan Gilbert (git)
2020-01-13 17:36 ` [PATCH v2 2/3] memory: Allow a MemoryRegion to be marked no_vhost Dr. David Alan Gilbert (git)
2020-01-14 7:19 ` Michael S. Tsirkin
2020-01-14 11:26 ` Dr. David Alan Gilbert
2020-01-14 14:52 ` Michael S. Tsirkin
2020-01-14 15:02 ` Alex Williamson
2020-01-13 17:36 ` [PATCH v2 3/3] hyperv/synic: Mark regions as no vhost Dr. David Alan Gilbert (git)
2020-01-13 18:13 ` [PATCH v2 0/3] exclude hyperv synic sections from vhost Paolo Bonzini
2020-01-13 18:58 ` Dr. David Alan Gilbert
2020-01-14 7:17 ` Michael S. Tsirkin
2020-01-17 12:35 ` Dr. David Alan Gilbert
2020-01-15 12:12 ` Roman Kagan [this message]
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