On Wed, May 22, 2024 at 04:09:41PM +0200, David Hildenbrand wrote: > On 21.05.24 14:57, Brendan Jackman wrote: > The old seqlock guaranteed that we would have obtained consistent values > here. start + spanned_pages defines a range. For example, growing a zone to > the beginning implies that both ranges must be changed. > > I do wonder if it might be better to instead have zone->zone_start_pfn and > zone->zone_end_pfn. That way, both can be changed individually, not > requiring adjustment of both to grow/shrink a zone at the beginning. Thanks this is a good point. So basically the fact that spanned_pages is "once or eventually" correct is certainly not enough because it only has meaning with reference to zone_start_pfn. I didn't realise this because of my spontaneous inspiration to believe that zone_start_pfn was fixed. By the way, some noob questions: am I OK with my assumption that it's fine for reader code to operate on zone spans that are both stale and "from the future"? thinking abstractly I guess that seeing a stale value when racing with offline_pages is roughly the same as seeing a value "from the future" when racing with online_pages? Also, is it ever possible for pages to get removed and then added back and end up in a different zone than before?
