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Date: Tue, 22 Jan 2019 13:47:08 -0500
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH V9 4/6] util/mmap-alloc: support MAP_SYNC
 in qemu_ram_mmap()
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To: Dan Williams <dan.j.williams@intel.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>, Pankaj Gupta <pagupta@redhat.com>, Qemu Developers <qemu-devel@nongnu.org>, yu.c.zhang@linux.intel.com, Stefan Hajnoczi <stefanha@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Xiao Guangrong <xiaoguangrong.eric@gmail.com>

On Tue, Jan 22, 2019 at 09:33:37AM -0800, Dan Williams wrote:
> On Mon, Jan 21, 2019 at 7:27 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> [..]
> > > 2. The reset of cases:
> > >       - we will never pass the MAP_SYNC to mmap2
> >
> > I don't see code probing for MAP_SYNC support. Did I miss it?
> > But if all you want is to have old linux ignore MAP_SYNC,
> > I think you got your wish automatically - just do not set
> > MAP_SHARED_VALIDATE.
> 
> That will also cause new Linux to ignore MAP_SYNC.

Oh you are right. I missed this point.

And given that these patches do not seem to set MAP_SHARED_VALIDATE
at all I conclude that even though thet set MAP_SYNC
it actually has no effect at all.

So I wonder how they were tested.
Would the contributors care to elaborate?
That would be good info to put in the commit log message.

-- 
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