Re: [PATCH] migrate/ram: let ram_save_target_page_legacy() return if qemu file got error

[Fabiano Rosas <farosas@suse.de>]

Guoyi Tu <tugy@chinatelecom.cn> writes:

> When the migration process of a virtual machine using huge pages is 
> cancelled,
> QEMU will continue to complete the processing of the current huge page
> through the qemu file object got an error set. These processing, such as
> compression and encryption, will consume a lot of CPU resources which may
> affact the the performance of the other VMs.
>
> To terminate the migration process more quickly and minimize unnecessary
> resource occupancy, it's neccessary to add logic to check the error status
> of qemu file object in the beginning of ram_save_target_page_legacy 
> function,
> and make sure the function returns immediately if qemu file got an error.
>
> Signed-off-by: Guoyi Tu <tugy@chinatelecom.cn>
> ---
>   migration/ram.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/migration/ram.c b/migration/ram.c
> index 9040d66e61..3e2ebf3004 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -2133,6 +2133,10 @@ static int ram_save_target_page_legacy(RAMState 
> *rs, PageSearchStatus *pss)
>       ram_addr_t offset = ((ram_addr_t)pss->page) << TARGET_PAGE_BITS;
>       int res;
>
> +    if (qemu_file_get_error(pss->pss_channel)) {
> +        return -1;
> +    }

Where was the error set? Is this from cancelling via QMP? Or something
from within ram_save_target_page_legacy? We should probably make the
check closer to where the error happens. At the very least moving the
check into the loop.