commit 211ea74022f51164a7729030b28eec90b6c99a08
author Peter Lieven <pl@kamp.de> Mon Jun 10 12:14:20 2013 +0200
committer Juan Quintela <quintela@redhat.com> Thu Jun 27 02:36:32 2013 +0200
tree 58f143a42096d24fe5f996fe971eb92c55546be4
parent 9ef051e5536b6368a1076046ec6c4ec4ac12b5c6

migration: do not overwrite zero pages

on incoming migration do not memset pages to zero if they already read as zero.
this will allocate a new zero page and consume memory unnecessarily. even
if we madvise a MADV_DONTNEED later this will only deallocate the memory
asynchronously.

Signed-off-by: Peter Lieven <pl@kamp.de>
Signed-off-by: Juan Quintela <quintela@redhat.com>

arch_init.c

diff --git a/arch_init.c b/arch_init.c
index 8bb933f..4dd17f4 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -835,14 +835,16 @@
             }
 
             ch = qemu_get_byte(f);
-            memset(host, ch, TARGET_PAGE_SIZE);
+            if (ch != 0 || !is_zero_page(host)) {
+                memset(host, ch, TARGET_PAGE_SIZE);
 #ifndef _WIN32
-            if (ch == 0 &&
-                (!kvm_enabled() || kvm_has_sync_mmu()) &&
-                getpagesize() <= TARGET_PAGE_SIZE) {
-                qemu_madvise(host, TARGET_PAGE_SIZE, QEMU_MADV_DONTNEED);
-            }
+                if (ch == 0 &&
+                    (!kvm_enabled() || kvm_has_sync_mmu()) &&
+                    getpagesize() <= TARGET_PAGE_SIZE) {
+                    qemu_madvise(host, TARGET_PAGE_SIZE, QEMU_MADV_DONTNEED);
+                }
 #endif
+            }
         } else if (flags & RAM_SAVE_FLAG_PAGE) {
             void *host;