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From: Juan Quintela <quintela@redhat.com>
In-Reply-To: <1443515898-3594-42-git-send-email-dgilbert@redhat.com> (David
	Alan Gilbert's message of "Tue, 29 Sep 2015 09:38:05 +0100")
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	<1443515898-3594-42-git-send-email-dgilbert@redhat.com>
Date: Wed, 28 Oct 2015 11:28:26 +0100
Message-ID: <87d1vz9tit.fsf@neno.neno>
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Subject: Re: [Qemu-devel] [PATCH v8 41/54] postcopy_ram.c: place_page and
	helpers
Reply-To: quintela@redhat.com
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To: "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>
Cc: aarcange@redhat.com, liang.z.li@intel.com, qemu-devel@nongnu.org, luis@cs.umu.se, bharata@linux.vnet.ibm.com, amit.shah@redhat.com, pbonzini@redhat.com

"Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>
> postcopy_place_page (etc) provide a way for postcopy to place a page
> into guests memory atomically (using the copy ioctl on the ufd).
>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Reviewed-by: Amit Shah <amit.shah@redhat.com>


Reviewed-by: Juan Quintela <quintela@redhat.com>

> +int postcopy_place_page_zero(MigrationIncomingState *mis, void *host)
> +{
> +    struct uffdio_zeropage zero_struct;
> +
> +    zero_struct.range.start = (uint64_t)(uintptr_t)host;
> +    zero_struct.range.len = getpagesize();
> +    zero_struct.mode = 0;
> +
> +    if (ioctl(mis->userfault_fd, UFFDIO_ZEROPAGE, &zero_struct)) {
> +        int e = errno;
> +        error_report("%s: %s zero host: %p",
> +                     __func__, strerror(e), host);
> +
> +        return -e;
> +    }
> +
> +    trace_postcopy_place_page_zero(host);
> +    return 0;
> +}

Would this be faster than normal precopy way of just copying a zero page?