Re: [RFC Get rid of shrink code - memory-hotplug]

[Michal Hocko <mhocko@suse.com>]

On Mon 10-12-18 14:53:22, osalvador@suse.de wrote:
> On 2018-12-07 11:35, osalvador@suse.de wrote:
> > On 2018-12-07 11:32, Michal Hocko wrote:
> > > On Fri 07-12-18 10:54:50, Vlastimil Babka wrote:
> > > > Well, __pageblock_pfn_to_page() has to be called for each
> > > > pageblock in
> > > > compaction, when zone_contiguous is false. And that's unchanged since
> > > > the introduction of zone_contiguous, so the numbers should still
> > > > hold.
> > > 
> > > OK, this means that we have to carefully re-evaluate zone_contiguous
> > > for
> > > each offline operation.
> 
> I started to think about this but some questions arose.
> 
> Actually, no matter what we do, if we re-evaluate zone_contiguous
> in the offline operation, zone_contiguous will be left unset.
> 
> set_zone_contiguous() calls __pageblock_pfn_to_page() in
> pageblock_nr_pages chunks to determine if the zone is contiguous,
> and checks the following:
> 
> * first/end pfn of the pageblock are valid sections
> * first pfn of the pageblock is online
> * we do not intersect different zones
> * first/end pfn belong to the same zone
> 
> Now, when dropping the shrink code and re-evaluating zone_contiguous in
> offline
> operation, set_zone_contiguous() will return false, leaving us with
> zone_contiguous
> unset.

Yeah. But does anything prevent us to alter the logic that the zone is
not contiguous iff there are offline holes or zones intermixed.
-- 
Michal Hocko
SUSE Labs