Re: [Qemu-devel] [PATCH COLO-Frame v15 29/38] COLO: Separate the process of saving/loading ram and device state

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

* zhanghailiang (zhang.zhanghailiang@huawei.com) wrote:
> We separate the process of saving/loading ram and device state when do
> checkpoint, we add new helpers for save/load ram/device. With this change,
> we can directly transfer ram from master to slave without using
> QEMUSizeBufferas as assistant, which also reduce the size of extra memory
> been used during checkpoint.
> 
> Besides, we move the colo_flush_ram_cache to the proper position after the
> above change.
> 
> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> ---
> v14:
> - split two new patches from this patch
> - Some minor fixes from Dave
> v13:
> - Re-use some existed helper functions to realize saving/loading
>   ram and device.
> v11:
> - Remove load configuration section in qemu_loadvm_state_begin()
> ---
>  migration/colo.c   | 48 ++++++++++++++++++++++++++++++++++++++----------
>  migration/ram.c    |  5 -----
>  migration/savevm.c |  5 +++++
>  3 files changed, 43 insertions(+), 15 deletions(-)
> 
> diff --git a/migration/colo.c b/migration/colo.c
> index 16bada6..300fa54 100644
> --- a/migration/colo.c
> +++ b/migration/colo.c
> @@ -288,21 +288,37 @@ static int colo_do_checkpoint_transaction(MigrationState *s,
>          goto out;
>      }
>  
> +    colo_put_cmd(s->to_dst_file, COLO_MESSAGE_VMSTATE_SEND, &local_err);
> +    if (local_err) {
> +        goto out;
> +    }
> +
>      /* Disable block migration */
>      s->params.blk = 0;
>      s->params.shared = 0;
> -    qemu_savevm_state_header(trans);
> -    qemu_savevm_state_begin(trans, &s->params);
> +    qemu_savevm_state_begin(s->to_dst_file, &s->params);
> +    ret = qemu_file_get_error(s->to_dst_file);
> +    if (ret < 0) {
> +        error_report("Save vm state begin error");
> +        goto out;
> +    }
> +
>      qemu_mutex_lock_iothread();
> -    qemu_savevm_state_complete_precopy(trans, false);
> +    /*
> +    * Only save VM's live state, which not including device state.
> +    * TODO: We may need a timeout mechanism to prevent COLO process
> +    * to be blocked here.
> +    */
> +    qemu_savevm_live_state(s->to_dst_file);
> +    /* Note: device state is saved into buffer */
> +    ret = qemu_save_device_state(trans);
>      qemu_mutex_unlock_iothread();

Yes, I still worry a little about what can hang under that lock, but I think
it's the best we've got at the moment; we probably need to understand what
the rules are about what actually needs the lock!

Other than that,

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

> -
> -    qemu_fflush(trans);
> -
> -    colo_put_cmd(s->to_dst_file, COLO_MESSAGE_VMSTATE_SEND, &local_err);
> -    if (local_err) {
> +    if (ret < 0) {
> +        error_report("Save device state error");
>          goto out;
>      }
> +    qemu_fflush(trans);
> +
>      /* we send the total size of the vmstate first */
>      size = qsb_get_length(buffer);
>      colo_put_cmd_value(s->to_dst_file, COLO_MESSAGE_VMSTATE_SIZE,
> @@ -573,6 +589,16 @@ void *colo_process_incoming_thread(void *opaque)
>              goto out;
>          }
>  
> +        ret = qemu_loadvm_state_begin(mis->from_src_file);
> +        if (ret < 0) {
> +            error_report("Load vm state begin error, ret=%d", ret);
> +            goto out;
> +        }
> +        ret = qemu_loadvm_state_main(mis->from_src_file, mis);
> +        if (ret < 0) {
> +            error_report("Load VM's live state (ram) error");
> +            goto out;
> +        }
>          /* read the VM state total size first */
>          value = colo_get_cmd_value(mis->from_src_file,
>                                   COLO_MESSAGE_VMSTATE_SIZE, &local_err);
> @@ -605,8 +631,10 @@ void *colo_process_incoming_thread(void *opaque)
>          qemu_mutex_lock_iothread();
>          qemu_system_reset(VMRESET_SILENT);
>          vmstate_loading = true;
> -        if (qemu_loadvm_state(fb) < 0) {
> -            error_report("COLO: loadvm failed");
> +        colo_flush_ram_cache();
> +        ret = qemu_load_device_state(fb);
> +        if (ret < 0) {
> +            error_report("COLO: load device state failed");
>              qemu_mutex_unlock_iothread();
>              goto out;
>          }
> diff --git a/migration/ram.c b/migration/ram.c
> index 891f3b2..8f416d5 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2465,7 +2465,6 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>       * be atomic
>       */
>      bool postcopy_running = postcopy_state_get() >= POSTCOPY_INCOMING_LISTENING;
> -    bool need_flush = false;
>  
>      seq_iter++;
>  
> @@ -2500,7 +2499,6 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>              /* After going into COLO, we should load the Page into colo_cache */
>              if (ram_cache_enable) {
>                  host = colo_cache_from_block_offset(block, addr);
> -                need_flush = true;
>              } else {
>                  host = host_from_ram_block_offset(block, addr);
>              }
> @@ -2594,9 +2592,6 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
>  
>      rcu_read_unlock();
>  
> -    if (!ret  && ram_cache_enable && need_flush) {
> -        colo_flush_ram_cache();
> -    }
>      DPRINTF("Completed load of VM with exit code %d seq iteration "
>              "%" PRIu64 "\n", ret, seq_iter);
>      return ret;
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 60c7b57..1551fbb 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -50,6 +50,7 @@
>  #include "qemu/iov.h"
>  #include "block/snapshot.h"
>  #include "block/qapi.h"
> +#include "migration/colo.h"
>  
>  
>  #ifndef ETH_P_RARP
> @@ -923,6 +924,10 @@ void qemu_savevm_state_begin(QEMUFile *f,
>              break;
>          }
>      }
> +    if (migration_in_colo_state()) {
> +        qemu_put_byte(f, QEMU_VM_EOF);
> +        qemu_fflush(f);
> +    }
>  }
>  
>  /*
> -- 
> 1.8.3.1
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK