On Tue, Feb 27, 2024 at 8:02 PM Yin Fengwei <fengwei.yin@xxxxxxxxx> wrote: > > > > On 2/27/24 14:40, Barry Song wrote: > > On Tue, Feb 27, 2024 at 7:14 PM Yin Fengwei <fengwei.yin@xxxxxxxxx> wrote: > >> > >> > >> > >> On 2/27/24 10:17, Barry Song wrote: > >>>> Like if we hit folio which is partially mapped to the range, don't split it but > >>>> just unmap the mapping part from the range. Let page reclaim decide whether > >>>> split the large folio or not (If it's not mapped to any other range,it will be > >>>> freed as whole large folio. If part of it still mapped to other range,page reclaim > >>>> can decide whether to split it or ignore it for current reclaim cycle). > >>> Yes, we can. but we still have to play the ptes check game to avoid adding > >>> folios multiple times to reclaim the list. > >>> > >>> I don't see too much difference between splitting in madvise and splitting > >>> in vmscan. as our real purpose is avoiding splitting entirely mapped > >>> large folios. for partial mapped large folios, if we split in madvise, then > >>> we don't need to play the game of skipping folios while iterating PTEs. > >>> if we don't split in madvise, we have to make sure the large folio is only > >>> added in reclaimed list one time by checking if PTEs belong to the > >>> previous added folio. > >> > >> If the partial mapped large folio is unmapped from the range, the related PTE > >> become none. How could the folio be added to reclaimed list multiple times? > > > > in case we have 16 PTEs in a large folio. > > PTE0 present > > PTE1 present > > PTE2 present > > PTE3 none > > PTE4 present > > PTE5 none > > PTE6 present > > .... > > the current code is scanning PTE one by one. > > while scanning PTE0, we have added the folio. then PTE1, PTE2, PTE4, PTE6... > No. Before detect the folio is fully mapped to the range, we can't add folio > to reclaim list because the partial mapped folio shouldn't be added. We can > only scan PTE15 and know it's fully mapped. you never know PTE15 is the last one mapping to the large folio, PTE15 can be mapping to a completely different folio with PTE0. > > So, when scanning PTE0, we will not add folio. Then when hit PTE3, we know > this is a partial mapped large folio. We will unmap it. Then all 16 PTEs > become none. I don't understand why all 16PTEs become none as we set PTEs to none. we set PTEs to swap entries till try_to_unmap_one called by vmscan. > > If the large folio is fully mapped, the folio will be added to reclaim list > after scan PTE15 and know it's fully mapped. our approach is calling pte_batch_pte while meeting the first pte, if pte_batch_pte = 16, then we add this folio to reclaim_list and skip the left 15 PTEs. > > Regards > Yin, Fengwei > > > > > there are all kinds of possibilities for unmapping. > > > > so what we can do is recording we have added the folio while scanning PTE0, > > then skipping this folios for all other PTEs. > > > > otherwise, we can split it while scanning PTE0, then we will meet > > different folios > > afterwards. > > > >> > >> > >> Regards > >> Yin, Fengwei > > Thanks Barry
