[Qemu-devel] [PATCH] fix migration with large mem

[Izik Eidus <ieidus@redhat.com>]

From f881b371e08760a67bf1f5b992a586c3de600f7a Mon Sep 17 00:00:00 2001
From: Izik Eidus <ieidus@redhat.com>
Date: Tue, 13 Apr 2010 12:24:57 +0300
Subject: [PATCH] fix migration with large mem

In cases of guests with large mem that have pages
that all their bytes content are the same, we will
spend alot of time reading the memory from the guest
(is_dup_page())

It is happening beacuse ram_save_live() function have
limit of how much we can send to the dest but not how
much we read from it, and in cases we have many is_dup_page()
hits, we might read huge amount of data without updating important
stuff like the timers...

The guest lose all its repsonsibility and have many softlock ups
inside itself.

this patch add limit on the size we can read from the guest each
iteration.

    Thanks.

Signed-off-by: Izik Eidus <ieidus@redhat.com>
---
 arch_init.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/arch_init.c b/arch_init.c
index cfc03ea..e27b1a0 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -88,6 +88,8 @@ const uint32_t arch_type = QEMU_ARCH;
 #define RAM_SAVE_FLAG_PAGE	0x08
 #define RAM_SAVE_FLAG_EOS	0x10
 
+#define MAX_SAVE_BLOCK_READ 10 * 1024 * 1024
+
 static int is_dup_page(uint8_t *page, uint8_t ch)
 {
     uint32_t val = ch << 24 | ch << 16 | ch << 8 | ch;
@@ -175,6 +177,7 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, void *opaque)
     uint64_t bytes_transferred_last;
     double bwidth = 0;
     uint64_t expected_time = 0;
+    int data_read = 0;
 
     if (stage < 0) {
         cpu_physical_memory_set_dirty_tracking(0);
@@ -205,10 +208,11 @@ int ram_save_live(Monitor *mon, QEMUFile *f, int stage, void *opaque)
     bytes_transferred_last = bytes_transferred;
     bwidth = qemu_get_clock_ns(rt_clock);
 
-    while (!qemu_file_rate_limit(f)) {
+    while (!qemu_file_rate_limit(f) && data_read < MAX_SAVE_BLOCK_READ) {
         int ret;
 
         ret = ram_save_block(f);
+        data_read += ret * TARGET_PAGE_SIZE;
         bytes_transferred += ret * TARGET_PAGE_SIZE;
         if (ret == 0) { /* no more blocks */
             break;
-- 
1.6.6.1