Re: [Qemu-devel] [PATCH COLO-Frame v11 15/39] 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>
> ---
> v11:
> - Rename 'host_cache' to 'colo_cache' (Dave's suggestion)
> v10:
> - Split the process of dirty pages recording into a new patch
> ---
>  include/exec/ram_addr.h       |  1 +
>  include/migration/migration.h |  4 +++
>  migration/colo.c              | 10 +++++++
>  migration/ram.c               | 69 ++++++++++++++++++++++++++++++++++++++++++-
>  4 files changed, 83 insertions(+), 1 deletion(-)
> 
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index 7115154..bb44f66 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -26,6 +26,7 @@ struct RAMBlock {
>      struct rcu_head rcu;
>      struct MemoryRegion *mr;
>      uint8_t *host;
> +    uint8_t *colo_cache; /* For colo, VM's ram cache */
>      ram_addr_t offset;
>      ram_addr_t used_length;
>      ram_addr_t max_length;
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index ba5bcec..e41372d 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -332,4 +332,8 @@ int ram_save_queue_pages(MigrationState *ms, const char *rbname,
>  PostcopyState postcopy_state_get(void);
>  /* Set the state and return the old state */
>  PostcopyState postcopy_state_set(PostcopyState new_state);
> +
> +/* 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 012d8e5..6e933fa 100644
> --- a/migration/colo.c
> +++ b/migration/colo.c
> @@ -304,6 +304,12 @@ void *colo_process_incoming_thread(void *opaque)
>      qemu_set_block(qemu_get_fd(mis->from_src_file));
>  
>  
> +    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;
> @@ -353,6 +359,10 @@ 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 a161620..9d946a1 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -223,6 +223,7 @@ 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;
>  
> @@ -2175,6 +2176,16 @@ static inline void *host_from_ram_block_offset(RAMBlock *block,
>      return block->host + offset;
>  }
>  
> +static inline void *colo_cache_from_block_offset(RAMBlock *block,
> +                                                 ram_addr_t offset)
> +{
> +    if (!block) {
> +        return NULL;
> +    }
> +
> +    return block->colo_cache + offset;
> +}
> +
>  /*
>   * If a page (or a whole RDMA chunk) has been
>   * determined to be zero, then zap it.
> @@ -2454,7 +2465,12 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>                       RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) {
>              RAMBlock *block = ram_block_from_stream(f, addr, flags);
>  
> -            host = host_from_ram_block_offset(block, addr);
> +            /* After going into COLO, we should load the Page into colo_cache */
> +            if (ram_cache_enable) {
> +                host = colo_cache_from_block_offset(block, addr);
> +            } else {
> +                host = host_from_ram_block_offset(block, addr);
> +            }
>              if (!host) {
>                  error_report("Illegal RAM offset " RAM_ADDR_FMT, addr);
>                  ret = -EINVAL;
> @@ -2550,6 +2566,57 @@ 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->colo_cache = qemu_anon_ram_alloc(block->used_length, NULL);
> +        if (!block->colo_cache) {
> +            error_report("%s: Can't alloc memory for colo cache of block %s,"
> +                         "size %zu", __func__, block->idstr,
> +                         block->used_length);

Minor one that I didn't spot before;  I think that has to be RAM_ADDR_FMT instead of %zu

However, other than that;

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Dave

> +            goto out_locked;
> +        }
> +        memcpy(block->colo_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->colo_cache) {
> +            qemu_anon_ram_free(block->colo_cache, block->used_length);
> +            block->colo_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->colo_cache) {
> +            qemu_anon_ram_free(block->colo_cache, block->used_length);
> +            block->colo_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