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Re: [Qemu-devel] [PATCH 3/4] exec, memory: Call to xen_modified_memory.

From: Anthony PERARD
Subject: Re: [Qemu-devel] [PATCH 3/4] exec, memory: Call to xen_modified_memory.
Date: Tue, 17 Jul 2012 14:59:07 +0100
User-agent: Mozilla/5.0 (X11; Linux i686; rv:13.0) Gecko/20120614 Thunderbird/13.0.1

On 17/07/12 14:37, Avi Kivity wrote:
On 07/17/2012 04:30 PM, Anthony PERARD wrote:
This patch add some calls to xen_modified_memory to notify Xen about dirtybits
during migration.

diff --git a/exec.c b/exec.c
index c9fa17d..9f7a4f7 100644
--- a/exec.c
+++ b/exec.c
@@ -3438,6 +3438,7 @@ void cpu_physical_memory_rw(target_phys_addr_t addr, 
uint8_t *buf,
                          addr1, (0xff & ~CODE_DIRTY_FLAG));
+                xen_modified_memory(addr1, TARGET_PAGE_SIZE);
          } else {

This is pretty ugly.  An alternative is to set up a periodic bitmap scan
that looks at the qemu dirty bitmap and calls xen_modified_memory() for
dirty page ranges, and clears the bitmap for the next pass.  Is it workable?

I don't think a periodic scan can do anything useful, unfortunately.

(is xen_modified_memory a hypercall, or does it maintain an in-memory

It's an hypercall. The function do something (call the hypercall) only during migration, otherwise it return immediately.

Anthony PERARD

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