On Mon, Nov 18, 2024 at 05:14:14PM +1300, Barry Song wrote: > On Mon, Nov 18, 2024 at 5:03 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > On Sat, Nov 16, 2024 at 09:16:58AM +0000, Chen Ridong wrote: > > > 2. In shrink_page_list function, if folioN is THP(2M), it may be splited > > > and added to swap cache folio by folio. After adding to swap cache, > > > it will submit io to writeback folio to swap, which is asynchronous. > > > When shrink_page_list is finished, the isolated folios list will be > > > moved back to the head of inactive lru. The inactive lru may just look > > > like this, with 512 filioes have been move to the head of inactive lru. > > > > I was hoping that we'd be able to stop splitting the folio when adding > > to the swap cache. Ideally. we'd add the whole 2MB and write it back > > as a single unit. > > This is already the case: adding to the swapcache doesn’t require splitting > THPs, but failing to allocate 2MB of contiguous swap slots will. Agreed we need to understand why this is happening. As I've said a few times now, we need to stop requiring contiguity. Real filesystems don't need the contiguity (they become less efficient, but they can scatter a single 2MB folio to multiple places). Maybe Chris has a solution to this in the works?
