On 08/08/2018 12:52 PM, Peter Xu wrote:
On Tue, Aug 07, 2018 at 05:12:06PM +0800, guangrong.xiao@xxxxxxxxx wrote:From: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxx> flush_compressed_data() needs to wait all compression threads to finish their work, after that all threads are free until the migration feeds new request to them, reducing its call can improve the throughput and use CPU resource more effectively We do not need to flush all threads at the end of iteration, the data can be kept locally until the memory block is changed or memory migration starts over in that case we will meet a dirtied page which may still exists in compression threads's ring Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxx> --- migration/ram.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/migration/ram.c b/migration/ram.c index 99ecf9b315..55966bc2c1 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -306,6 +306,8 @@ struct RAMState { uint64_t iterations; /* number of dirty bits in the bitmap */ uint64_t migration_dirty_pages; + /* last dirty_sync_count we have seen */ + uint64_t dirty_sync_count_prev; /* protects modification of the bitmap */ QemuMutex bitmap_mutex; /* The RAMBlock used in the last src_page_requests */ @@ -3173,6 +3175,17 @@ static int ram_save_iterate(QEMUFile *f, void *opaque)ram_control_before_iterate(f, RAM_CONTROL_ROUND); + /*+ * if memory migration starts over, we will meet a dirtied page which + * may still exists in compression threads's ring, so we should flush + * the compressed data to make sure the new page is not overwritten by + * the old one in the destination. + */ + if (ram_counters.dirty_sync_count != rs->dirty_sync_count_prev) { + rs->dirty_sync_count_prev = ram_counters.dirty_sync_count; + flush_compressed_data(rs);AFAIU this only happens when ram_save_pending() calls migration_bitmap_sync(). Could we just simply flush there? Then we can avoid that new variable.
Yup, that's better indeed, will do it.
