Re: [PATCH v5 1/4] migration: introduce 'background-snapshot' migration capability

[Andrey Gruzdev]

On 08.12.2020 18:47, Peter Xu wrote:

> On Fri, Dec 04, 2020 at 12:31:00PM +0300, Andrey Gruzdev wrote:
> > +static
> > +WriteTrackingSupport migrate_query_write_tracking(void)
> > +{
> > +    static WriteTrackingSupport wt_support = WT_SUPPORT_UNKNOWN;
> >       
> Better to be non-static - consider uncompatible memory can be hot plugged after
> it's once set.
>
> With static removed (I think most of below if clauses can be unwrapped too, but
> your call), feel free to add:
>
> Reviewed-by: Peter Xu <peterx@redhat.com>
>
> Thanks,
>     
Yes, quite possible case with memory hot plug that you mentioned..
Thanks, I'll change it to non-static.
> > +
> > +    /* Check UFFD-IO and memory backends for compatibility only once */
> > +    if (wt_support == WT_SUPPORT_UNKNOWN) {
> > +        wt_support = WT_SUPPORT_ABSENT;
> > +        /* Check if kernel supports required UFFD features */
> > +        if (ram_write_tracking_available()) {
> > +            wt_support = WT_SUPPORT_AVAILABLE;
> > +            /*
> > +             * Check if current memory configuration is
> > +             * compatible with required UFFD features.
> > +             */
> > +            if (ram_write_tracking_compatible()) {
> > +                wt_support = WT_SUPPORT_COMPATIBLE;
> > +            }
> > +        }
> > +    }
> > +
> > +    return wt_support;
> > +}
> > +#endif /* CONFIG_LINUX */
> >       
>