Count used RAMBlock pages for migration_dirty_p

PATCH Superseded Dr. David Alan Gilbert (git) 1 participant 1 message Mar 21, 2014

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Dr. David Alan Gilbert (git)

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2014-03-21 17:54 UTC #0 lore raw

PATCH v2 1/1 Count used RAMBlock pages for migration_dirty_p

From: "Dr. David Alan Gilbert" <[email protected]>

This is a fix for a bug* triggered by a migration after hot unplugging a few virtio-net NICs, that caused migration never to converge, because 'migration_dirty_pages' is incorrectly initialised.

'migration_dirty_pages' is used as a tally of the number of outstanding dirty pages, to give the migration code an idea of how much more data will need to be transferred, and thus whether it can end the iterative phase.

It was initialised to the total size of the RAMBlock address space, however hotunplug can leave this space sparse, and hence migration_dirty_pages ended up too large.

Signed-off-by Dr. David Alan Gilbert <address@hidden>

(* https://bugzilla.redhat.com/show_bug.cgi?id=1074913 )

---
 arch_init.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

v2:
Don't worry about RAMBlocks sharing a page; it doesn't happen

arch_init.c +17 -4

index f18f42e..47a1e44 100644
@@ -727,11 +727,8 @@ static void reset_ram_globals(void)
 static int ram_save_setup(QEMUFile *f, void *opaque)
 {
     RAMBlock *block;
-    int64_t ram_pages = last_ram_offset() >> TARGET_PAGE_BITS;
+    int64_t ram_bitmap_pages; /* Size of bitmap in pages, including gaps */
 
-    migration_bitmap = bitmap_new(ram_pages);
-    bitmap_set(migration_bitmap, 0, ram_pages);
-    migration_dirty_pages = ram_pages;
     mig_throttle_on = false;
     dirty_rate_high_cnt = 0;

@@ -770,6 +767,22 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     bytes_transferred = 0;
     reset_ram_globals();
 
+    ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS;
+    migration_bitmap = bitmap_new(ram_bitmap_pages);
+    bitmap_set(migration_bitmap, 0, ram_bitmap_pages);
+
+    /*
+     * Count the total number of pages used by ram blocks not including any
+     * gaps due to alignment or unplugs.
+     */
+    migration_dirty_pages = 0;
+    QTAILQ_FOREACH(block, &ram_list.blocks, next) {
+        uint64_t block_pages = 0;
+
+        block_pages = (block->length + TARGET_PAGE_SIZE - 1) / TARGET_PAGE_SIZE;
+        migration_dirty_pages += block_pages;
+    }
+
     memory_global_dirty_log_start();
     migration_bitmap_sync();
     qemu_mutex_unlock_iothread();

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