Re: [PATCH RFC] memory: Don't allow to resize RAM while migrating

[Juan Quintela <quintela@redhat.com>]

David Hildenbrand <david@redhat.com> wrote:

I agree with the removed bits.


> diff --git a/migration/ram.c b/migration/ram.c
> index ed23ed1c7c..f86f32b453 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -52,6 +52,7 @@
>  #include "migration/colo.h"
>  #include "block.h"
>  #include "sysemu/sysemu.h"
> +#include "sysemu/runstate.h"
>  #include "savevm.h"
>  #include "qemu/iov.h"
>  #include "multifd.h"
> @@ -3710,8 +3711,49 @@ static SaveVMHandlers savevm_ram_handlers = {
>      .resume_prepare = ram_resume_prepare,
>  };
>  
> +static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,
> +                                      size_t old_size, size_t new_size)
> +{
> +    /*
> +     * We don't care about resizes triggered on incoming migration (when
> +     * syncing ram blocks), or of course, when no migration is going on.
> +     */
> +    if (migration_is_idle() || !runstate_is_running()) {
> +        return;
> +    }
> +
> +    if (!postcopy_is_running()) {
> +        Error *err = NULL;
> +
> +        /*
> +         * Precopy code cannot deal with the size of ram blocks changing at
> +         * random points in time. We're still running on the source, abort
> +         * the migration and continue running here. Make sure to wait until
> +         * migration was canceled.
> +         */
> +        error_setg(&err, "RAM resized during precopy.");
> +        migrate_set_error(migrate_get_current(), err);
> +        error_free(err);
> +        migration_cancel();

If we can't do anything else, this is reasonable.

But as discussed before, it is still not fully clear to me _why_ are
ramblocks changing if we have disabled add/remove memory during migration.

> +    } else {
> +        /*
> +         * Postcopy code cannot deal with the size of ram blocks changing at
> +         * random points in time. We're running on the target. Fail hard.
> +         *
> +         * TODO: How to handle this in a better way?
> +         */
> +        error_report("RAM resized during postcopy.");
> +        exit(-1);

Idea is good, but we also need to exit destination, not only source, no?

> +    }
> +}



> +static RAMBlockNotifier ram_mig_ram_notifier = {
> +    .ram_block_resized = ram_mig_ram_block_resized,
> +};
> +
>  void ram_mig_init(void)
>  {
>      qemu_mutex_init(&XBZRLE.lock);
>      register_savevm_live("ram", 0, 4, &savevm_ram_handlers, &ram_state);
> +    ram_block_notifier_add(&ram_mig_ram_notifier);
>  }

Shouldn't we remove the notifier when we finish the migration.

Later, Juan.