On 12.04.22 15:42, Miaohe Lin wrote: > On 2022/4/12 16:59, Oscar Salvador wrote: >> On Sat, Apr 09, 2022 at 05:34:53PM +0800, Miaohe Lin wrote: >>> We don't need to check can_split_folio() because folio_maybe_dma_pinned() >>> is checked before. It will avoid the long term pinned pages to be swapped >>> out. And we can live with short term pinned pages. Without can_split_folio >>> checking we can simplify the code. Also activate_locked can be changed to >>> keep_locked as it's just short term pinning. >> >> What do you mean by "we can live with short term pinned pages"? >> Does it mean that it was not pinned when we check >> folio_maybe_dma_pinned() but now it is? >> >> To me it looks like the pinning is fluctuating and we rely on >> split_folio_to_list() to see whether we succeed or not, and if not >> we give it another spin in the next round? > > Yes. Short term pinned pages is relative to long term pinned pages and these pages won't be > pinned for a noticeable time. So it's expected to split the folio successfully in the next > round as the pinning is really fluctuating. Or am I miss something? > Just so we're on the same page. folio_maybe_dma_pinned() only capture FOLL_PIN, but not FOLL_GET. You can have long-term FOLL_GET right now via vmsplice(). can_split_folio() is more precise then folio_maybe_dma_pinned(), but both are racy as long as the page is still mapped. -- Thanks, David / dhildenb
