Re: [PATCH 1/2] migration: Prioritize RDMA in ram_save_target_page()

[Fabiano Rosas <farosas@suse.de>]

Li Zhijian via <qemu-devel@nongnu.org> writes:

> Address an error in RDMA-based migration by ensuring RDMA is prioritized
> when saving pages in `ram_save_target_page()`.
>
> Previously, the RDMA protocol's page-saving step was placed after other
> protocols due to a refactoring in commit bc38dc2f5f3. This led to migration
> failures characterized by unknown control messages and state loading errors
> destination:
> (qemu) qemu-system-x86_64: Unknown control message QEMU FILE
> qemu-system-x86_64: error while loading state section id 1(ram)
> qemu-system-x86_64: load of migration failed: Operation not permitted
> source:
> (qemu) qemu-system-x86_64: RDMA is in an error state waiting migration to abort!
> qemu-system-x86_64: failed to save SaveStateEntry with id(name): 1(ram): -1
> qemu-system-x86_64: rdma migration: recv polling control error!
> qemu-system-x86_64: warning: Early error. Sending error.
> qemu-system-x86_64: warning: rdma migration: send polling control error
>
> RDMA migration implemented its own protocol/method to send pages to
> destination side, hand over to RDMA first to prevent pages being saved by
> other protocol.
>
> Fixes: bc38dc2f5f3 ("migration: refactor ram_save_target_page functions")
> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
> ---
>  migration/ram.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/migration/ram.c b/migration/ram.c
> index 6f460fd22d2..635a2fe443a 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -1964,6 +1964,11 @@ static int ram_save_target_page(RAMState *rs, PageSearchStatus *pss)
>      ram_addr_t offset = ((ram_addr_t)pss->page) << TARGET_PAGE_BITS;
>      int res;
>  
> +    /* Hand over to RDMA first */
> +    if (control_save_page(pss, offset, &res)) {
> +        return res;
> +    }
> +

Can we hoist that migrate_rdma() from inside the function? Since the
other paths already check first before calling their functions.

>      if (!migrate_multifd()
>          || migrate_zero_page_detection() == ZERO_PAGE_DETECTION_LEGACY) {
>          if (save_zero_page(rs, pss, offset)) {
> @@ -1976,10 +1981,6 @@ static int ram_save_target_page(RAMState *rs, PageSearchStatus *pss)
>          return ram_save_multifd_page(block, offset);
>      }
>  
> -    if (control_save_page(pss, offset, &res)) {
> -        return res;
> -    }
> -
>      return ram_save_page(rs, pss);
>  }