ZONE_DEVICE and the future of struct page

Posted Mar 23, 2017 23:39 UTC (Thu) by Cyberax (✭ supporter ✭, #52523)
In reply to: ZONE_DEVICE and the future of struct page by djbw
Parent article: ZONE_DEVICE and the future of struct page

There are problems with that. Persistent memory is fast and durable, but not as fast and durable as the regular volatile RAM. So you have to put your page structures in the main RAM and this adds up quickly - a 2Tb persistent array will require around 32Gb or page structures.

ZONE_DEVICE struct page != ZONE_NORMAL struct page in terms of write rate

Posted Mar 24, 2017 0:15 UTC (Fri) by djbw (subscriber, #78104) [Link]

I'm not convinced that's going to be a problem in practice. Consider that the bulk of what makes struct page a frequently accessed data structure is when it is used by the core mm for general purpose page allocations. The ZONE_DEVICE mechanism never releases these pages for that high frequency usage. Another mitigation is that struct page writes are buffered by the cpu cache, which further reduces the write rate to media.