Re: [Qemu-devel] [PATCH] migration: always initial RAMBlock.bmap to 1 for new migration

[Wei Yang <richardw.yang@linux.intel.com>]

Thanks, I didn't notice this case.

On Sun, Jul 14, 2019 at 10:51:19PM +0800, Ivan Ren wrote:
>Reproduce the problem:
>migrate
>migrate_cancel
>migrate
>
>Error happen for memory migration
>
>The reason as follows:
>1. qemu start, ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] all set to
>   1 by a series of cpu_physical_memory_set_dirty_range
>2. migration start:ram_init_bitmaps
>   - memory_global_dirty_log_start: begin log diry

s/diry/dirty/

>   - memory_global_dirty_log_sync: sync dirty bitmap to
>     ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION]
>   - migration_bitmap_sync_range: sync ram_list.
>     dirty_memory[DIRTY_MEMORY_MIGRATION] to RAMBlock.bmap
>     and ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] is set to zero
>3. migration data...
>4. migrate_cancel, will stop log dirty
>5. migration start:ram_init_bitmaps
>   - memory_global_dirty_log_start: begin log diry

same as above

>   - memory_global_dirty_log_sync: sync dirty bitmap to
>     ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION]
>   - migration_bitmap_sync_range: sync ram_list.
>     dirty_memory[DIRTY_MEMORY_MIGRATION] to RAMBlock.bmap
>     and ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] is set to zero
>
>   Here RAMBlock.bmap only have new logged dirty pages, don't contain
>   the whole guest pages.
>
>Signed-off-by: Ivan Ren <ivanren@tencent.com>
>---
> migration/ram.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
>diff --git a/migration/ram.c b/migration/ram.c
>index 908517fc2b..bbebaee0c1 100644
>--- a/migration/ram.c
>+++ b/migration/ram.c
>@@ -3173,11 +3173,11 @@ static int ram_state_init(RAMState **rsp)
>     QSIMPLEQ_INIT(&(*rsp)->src_page_requests);
> 
>     /*
>+     * Count the total number of pages used by ram blocks not including any
>+     * gaps due to alignment or unplugs.
>      * This must match with the initial values of dirty bitmap.
>-     * Currently we initialize the dirty bitmap to all zeros so
>-     * here the total dirty page count is zero.
>      */
>-    (*rsp)->migration_dirty_pages = 0;
>+    (*rsp)->migration_dirty_pages = ram_bytes_total() >> TARGET_PAGE_BITS;
>     ram_state_reset(*rsp);
> 
>     return 0;
>@@ -3196,12 +3196,13 @@ static void ram_list_init_bitmaps(void)
>              * The initial dirty bitmap for migration must be set with all
>              * ones to make sure we'll migrate every guest RAM page to
>              * destination.
>-             * Here we didn't set RAMBlock.bmap simply because it is already
>-             * set in ram_list.dirty_memory[DIRTY_MEMORY_MIGRATION] in
>-             * ram_block_add, and that's where we'll sync the dirty bitmaps.
>-             * Here setting RAMBlock.bmap would be fine too but not necessary.
>+             * Here we set RAMBlock.bmap all to 1 because when rebegin a
>+             * new migration after a failed migration, ram_list.

It is after failure or cancel?

>+             * dirty_memory[DIRTY_MEMORY_MIGRATION] don't include the whole
>+             * guest memory.
>              */
>             block->bmap = bitmap_new(pages);
>+            bitmap_set(block->bmap, 0, pages);
>             if (migrate_postcopy_ram()) {
>                 block->unsentmap = bitmap_new(pages);
>                 bitmap_set(block->unsentmap, 0, pages);
>-- 
>2.17.2 (Apple Git-113)
>


Reviewed-by: Wei Yang <richardw.yang@linux.intel.com>

-- 
Wei Yang
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