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[Qemu-devel] [PATCH] Avoid loading ram pages that are all zeroes
From: |
Avi Kivity |
Subject: |
[Qemu-devel] [PATCH] Avoid loading ram pages that are all zeroes |
Date: |
Sun, 14 Dec 2008 19:14:33 +0200 |
Restoring or migrating zero pages causes unnecessary allocation of memory.
We can avoid this by dropping the loaded page instead of memset()ing it.
Signed-off-by: Avi Kivity <address@hidden>
diff --git a/vl.c b/vl.c
index 7b58605..42e97c9 100644
--- a/vl.c
+++ b/vl.c
@@ -3019,6 +3019,19 @@ void qemu_del_wait_object(HANDLE handle, WaitObjectFunc
*func, void *opaque)
/***********************************************************/
/* ram save/restore */
+static void drop_page(uint8_t *page)
+{
+ if (TARGET_PAGE_SIZE < getpagesize())
+ return;
+#ifdef CONFIG_KVM
+ if (kvm_enabled() && !kvm_has_sync_mmu())
+ return;
+#endif
+#ifdef MADV_DONTNEED
+ madvise(page, TARGET_PAGE_SIZE, MADV_DONTNEED);
+#endif
+}
+
static int ram_get_page(QEMUFile *f, uint8_t *buf, int len)
{
int v;
@@ -3032,6 +3045,8 @@ static int ram_get_page(QEMUFile *f, uint8_t *buf, int
len)
case 1:
v = qemu_get_byte(f);
memset(buf, v, len);
+ if (v == 0)
+ drop_page(buf);
break;
default:
return -EINVAL;
@@ -3289,6 +3304,8 @@ static int ram_load(QEMUFile *f, void *opaque, int
version_id)
if (flags & RAM_SAVE_FLAG_COMPRESS) {
uint8_t ch = qemu_get_byte(f);
memset(phys_ram_base + addr, ch, TARGET_PAGE_SIZE);
+ if (ch == 0)
+ drop_page(phys_ram_base + addr);
} else if (flags & RAM_SAVE_FLAG_PAGE)
qemu_get_buffer(f, phys_ram_base + addr, TARGET_PAGE_SIZE);
} while (!(flags & RAM_SAVE_FLAG_EOS));
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