Re: [Qemu-devel] [PATCH V10 08/20] ram/COLO: Record the dirty pages that SVM received

[Dr. David Alan Gilbert]

* Zhang Chen (address@hidden) wrote:
> We record the address of the dirty pages that received,
> it will help flushing pages that cached into SVM.
> 
> Here, it is a trick, we record dirty pages by re-using migration
> dirty bitmap. In the later patch, we will start the dirty log
> for SVM, just like migration, in this way, we can record both
> the dirty pages caused by PVM and SVM, we only flush those dirty
> pages from RAM cache while do checkpoint.
> 
> Signed-off-by: zhanghailiang <address@hidden>
> Reviewed-by: Dr. David Alan Gilbert <address@hidden>
> ---
>  migration/ram.c | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 33ebd09d70..d1060f1337 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -3325,6 +3325,15 @@ static inline void 
> *colo_cache_from_block_offset(RAMBlock *block,
>                       __func__, block->idstr);
>          return NULL;
>      }
> +
> +    /*
> +    * During colo checkpoint, we need bitmap of these migrated pages.
> +    * It help us to decide which pages in ram cache should be flushed
> +    * into VM's RAM later.
> +    */
> +    if (!test_and_set_bit(offset >> TARGET_PAGE_BITS, block->bmap)) {
> +        ram_state->migration_dirty_pages++;
> +    }
>      return block->colo_cache + offset;
>  }
>  
> @@ -3555,6 +3564,24 @@ int colo_init_ram_cache(void)
>          memcpy(block->colo_cache, block->host, block->used_length);
>      }
>      rcu_read_unlock();
> +    /*
> +    * Record the dirty pages that sent by PVM, we use this dirty bitmap 
> together
> +    * with to decide which page in cache should be flushed into SVM's RAM. 
> Here
> +    * we use the same name 'ram_bitmap' as for migration.
> +    */
> +    if (ram_bytes_total()) {
> +        RAMBlock *block;
> +
> +        QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {

I think those need updating to check for 'qemu_ram_is_migratable' - it
might be worth moving RAMBLOCK_FOREACH_MIGRATABLE.

> +            unsigned long pages = block->max_length >> TARGET_PAGE_BITS;
> +
> +            block->bmap = bitmap_new(pages);
> +            bitmap_set(block->bmap, 0, pages);

Would it make sense to use the 'receivedmap' that was recently added
for other uses rather than needing your own?

Dave

> +         }
> +    }
> +    ram_state = g_new0(RAMState, 1);
> +    ram_state->migration_dirty_pages = 0;
> +
>      return 0;
>  
>  out_locked:
> @@ -3574,6 +3601,10 @@ void colo_release_ram_cache(void)
>  {
>      RAMBlock *block;
>  
> +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> +        g_free(block->bmap);
> +        block->bmap = NULL;
> +    }
>      rcu_read_lock();
>      QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
>          if (block->colo_cache) {
> @@ -3582,6 +3613,8 @@ void colo_release_ram_cache(void)
>          }
>      }
>      rcu_read_unlock();
> +    g_free(ram_state);
> +    ram_state = NULL;
>  }
>  
>  /**
> -- 
> 2.17.1
> 
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK