Re: [Qemu-devel] [PATCH COLO-Frame v10 13/38] COLO: Load PVM's dirty pages into SVM's RAM cache temporarily

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* zhanghailiang (zhang.zhanghailiang@huawei.com) wrote:
> We should not load PVM's state directly into SVM, because there maybe some
> errors happen when SVM is receving data, which will break SVM.
> 
> We need to ensure receving all data before load the state into SVM. We use
> an extra memory to cache these data (PVM's ram). The ram cache in secondary side
> is initially the same as SVM/PVM's memory. And in the process of checkpoint,
> we cache the dirty pages of PVM into this ram cache firstly, so this ram cache
> always the same as PVM's memory at every checkpoint, then we flush this cached ram
> to SVM after we receive all PVM's state.
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
> ---
> v10: Split the process of dirty pages recording into a new patch
> ---
>  include/exec/ram_addr.h  |  1 +
>  include/migration/colo.h |  3 +++
>  migration/colo.c         | 14 +++++++++--
>  migration/ram.c          | 61 ++++++++++++++++++++++++++++++++++++++++++++++--
>  4 files changed, 75 insertions(+), 4 deletions(-)
> 
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index 3360ac5..e7c4310 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -28,6 +28,7 @@ struct RAMBlock {
>      struct rcu_head rcu;
>      struct MemoryRegion *mr;
>      uint8_t *host;
> +    uint8_t *host_cache; /* For colo, VM's ram cache */

I suggest you make the name have 'colo' in it; e.g. colo_cache;
'host_cache' is a bit generic.

>      ram_addr_t offset;
>      ram_addr_t used_length;
>      ram_addr_t max_length;
> diff --git a/include/migration/colo.h b/include/migration/colo.h
> index 2676c4a..8edd5f1 100644
> --- a/include/migration/colo.h
> +++ b/include/migration/colo.h
> @@ -29,4 +29,7 @@ bool migration_incoming_enable_colo(void);
>  void migration_incoming_exit_colo(void);
>  void *colo_process_incoming_thread(void *opaque);
>  bool migration_incoming_in_colo_state(void);
> +/* ram cache */
> +int colo_init_ram_cache(void);
> +void colo_release_ram_cache(void);
>  #endif
> diff --git a/migration/colo.c b/migration/colo.c
> index b865513..25f85b2 100644
> --- a/migration/colo.c
> +++ b/migration/colo.c
> @@ -304,6 +304,12 @@ void *colo_process_incoming_thread(void *opaque)
>          goto out;
>      }
>  
> +    ret = colo_init_ram_cache();
> +    if (ret < 0) {
> +        error_report("Failed to initialize ram cache");
> +        goto out;
> +    }
> +
>      ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_CHECKPOINT_READY, 0);
>      if (ret < 0) {
>          goto out;
> @@ -331,14 +337,14 @@ void *colo_process_incoming_thread(void *opaque)
>              goto out;
>          }
>  
> -        /* TODO: read migration data into colo buffer */
> +        /* TODO Load VM state */
>  
>          ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_VMSTATE_RECEIVED, 0);
>          if (ret < 0) {
>              goto out;
>          }
>  
> -        /* TODO: load vm state */
> +        /* TODO: flush vm state */

Do you really need to update/change the TODOs here?

>          ret = colo_ctl_put(mis->to_src_file, COLO_COMMAND_VMSTATE_LOADED, 0);
>          if (ret < 0) {
> @@ -352,6 +358,10 @@ out:
>                       strerror(-ret));
>      }
>  
> +    qemu_mutex_lock_iothread();
> +    colo_release_ram_cache();
> +    qemu_mutex_unlock_iothread();
> +
>      if (mis->to_src_file) {
>          qemu_fclose(mis->to_src_file);
>      }
> diff --git a/migration/ram.c b/migration/ram.c
> index 5784c15..b094dc3 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -222,6 +222,7 @@ static RAMBlock *last_sent_block;
>  static ram_addr_t last_offset;
>  static QemuMutex migration_bitmap_mutex;
>  static uint64_t migration_dirty_pages;
> +static bool ram_cache_enable;
>  static uint32_t last_version;
>  static bool ram_bulk_stage;
>  
> @@ -1446,7 +1447,11 @@ static inline void *host_from_stream_offset(QEMUFile *f,
>              return NULL;
>          }
>  
> -        return block->host + offset;
> +        if (ram_cache_enable) {
> +            return block->host_cache + offset;
> +        } else {
> +            return block->host + offset;
> +        }
>      }
>  
>      len = qemu_get_byte(f);
> @@ -1456,7 +1461,11 @@ static inline void *host_from_stream_offset(QEMUFile *f,
>      QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
>          if (!strncmp(id, block->idstr, sizeof(id)) &&
>              block->max_length > offset) {
> -            return block->host + offset;
> +            if (ram_cache_enable) {
> +                return block->host_cache + offset;
> +            } else {
> +                return block->host + offset;
> +            }
>          }
>      }
>  
> @@ -1707,6 +1716,54 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>      return ret;
>  }
>  
> +/*
> + * colo cache: this is for secondary VM, we cache the whole
> + * memory of the secondary VM, it will be called after first migration.
> + */
> +int colo_init_ram_cache(void)
> +{
> +    RAMBlock *block;
> +
> +    rcu_read_lock();
> +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> +        block->host_cache = qemu_anon_ram_alloc(block->used_length, NULL);
> +        if (!block->host_cache) {
> +            goto out_locked;
> +        }

Please print an error message; stating the function, block name and size that
failed.

> +        memcpy(block->host_cache, block->host, block->used_length);
> +    }
> +    rcu_read_unlock();
> +    ram_cache_enable = true;
> +    return 0;
> +
> +out_locked:
> +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> +        if (block->host_cache) {
> +            qemu_anon_ram_free(block->host_cache, block->used_length);
> +            block->host_cache = NULL;
> +        }
> +    }
> +
> +    rcu_read_unlock();
> +    return -errno;
> +}
> +
> +void colo_release_ram_cache(void)
> +{
> +    RAMBlock *block;
> +
> +    ram_cache_enable = false;
> +
> +    rcu_read_lock();
> +    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
> +        if (block->host_cache) {
> +            qemu_anon_ram_free(block->host_cache, block->used_length);
> +            block->host_cache = NULL;
> +        }
> +    }
> +    rcu_read_unlock();
> +}
> +
>  static SaveVMHandlers savevm_ram_handlers = {
>      .save_live_setup = ram_save_setup,
>      .save_live_iterate = ram_save_iterate,
> -- 
> 1.8.3.1
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK