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It is possible that >> the folio is unmapped fully, but it is unnecessary to add the folio >> to deferred split list at all. Fix it by checking folio->_nr_pages_map= ped >> before adding a folio to deferred split list. If the folio is already >> on the deferred split list, it will be skipped. This issue applies to >> both PTE-mapped THP and mTHP. >> >> Commit 98046944a159 ("mm: huge_memory: add the missing >> folio_test_pmd_mappable() for THP split statistics") tried to exclude >> mTHP deferred split stats from THP_DEFERRED_SPLIT_PAGE, but it does no= t >> fix the above issue. A fully unmapped PTE-mapped order-9 THP was still= > > Once again: your patch won't fix it either. > >> added to deferred split list and counted as THP_DEFERRED_SPLIT_PAGE, >> since nr is 512 (non zero), level is RMAP_LEVEL_PTE, and inside >> deferred_split_folio() the order-9 folio is folio_test_pmd_mappable().= >> However, this miscount was present even earlier due to implementation,= >> since PTEs are unmapped individually and first PTE unmapping adds the = THP >> into the deferred split list. > > It will still be present. Just less frequently. OK. Let me reread the email exchanges between you and Yang and clarify the details in the commit log. > >> >> With commit b06dc281aa99 ("mm/rmap: introduce >> folio_remove_rmap_[pte|ptes|pmd]()"), kernel is able to unmap PTE-mapp= ed >> folios in one shot without causing the miscount, hence this patch. >> >> Signed-off-by: Zi Yan >> Reviewed-by: Yang Shi >> --- >> mm/rmap.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/mm/rmap.c b/mm/rmap.c >> index a7913a454028..2809348add7b 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1553,9 +1553,10 @@ static __always_inline void __folio_remove_rmap= (struct folio *folio, >> * page of the folio is unmapped and at least one page >> * is still mapped. >> */ >> - if (folio_test_large(folio) && folio_test_anon(folio)) >> - if (level =3D=3D RMAP_LEVEL_PTE || nr < nr_pmdmapped) >> - deferred_split_folio(folio); >> + if (folio_test_large(folio) && folio_test_anon(folio) && >> + ((level =3D=3D RMAP_LEVEL_PTE && atomic_read(mapped)) || >> + (level =3D=3D RMAP_LEVEL_PMD && nr < nr_pmdmapped))) >> + deferred_split_folio(folio); > > Please refrain from posting a new patch before the discussion on the ol= d one is done. > > See my comments on v2 why optimizing out the function call is a reasona= ble thing to do *where we cannot batch* and the misaccounting will still = happen. But it can be done independently. Got it. Will keep the deferred list checking here and send a new one with= commit log changes too. Thank you for the reviews. -- Best Regards, Yan, Zi --=_MailMate_88369472-D40F-4247-8648-2A92C1E93C0C_= Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQJDBAEBCgAtFiEE6rR4j8RuQ2XmaZol4n+egRQHKFQFAmYqbncPHHppeUBudmlk aWEuY29tAAoJEOJ/noEUByhUAvkP/2Ek9m3XjgjHJHSn5uJ5CccVGind9sG+/uQ9 HZn98ap4OfjNTBguPRwl5YloFnsSzfQXVkG7+5iGn3j0uSppAcPUD6TkHq1KJ9M9 HrUTXPmeq4gQv72lL622HQ+lmHHsHhviyfEWnBBJCQahXMKsRaD7T97IlKKL0RCp tmdqEyFfBTiB9uMlj8dYXCz8FTEnapRqOfaOcU3OHmQFMxc5WJBLDc7Ug7eQ6Mbe I4TXv1AkQcXkrZgSu2m4t1lHughp+GwestQGVZe+75lGajmDMq2ZE4/o9ArzM9bw eDPGIZ4moevgWYjRHahwzeh8BI6uaf98M9O4dGP1TzQBQTQaIkTb3A7u3qqhEBS/ 3Zt8FFOS7VA8EDeRXHbwPk0LS80LUe5LkbV5Ryy3kvHwz1GxFHVVocV8HdHgRrmx /Nvu34+Mp/dQGNEuWNCBLXbpllvRpo9Vd/+xY6jJkdh4xLH/ZH99UXpbVE/i8HxC akQEUDaes+tDytG036ZaaxvwUOpMBHfpivPN5NSm5I0krtq3yasnKv7gf+/s1MEM Bi32BSTGqHXUVtyVyxC7Oug9jPevHCvURcy5PR5t9HJptMDV5gVdDLlrp2X4KgRb KZpt4e7U0slaPQAZdtEuAkI2hcqC+iZpc451MqtQxk/FUPumGEPsksv0ILajtOkE xt+tRalx =jmjC -----END PGP SIGNATURE----- --=_MailMate_88369472-D40F-4247-8648-2A92C1E93C0C_=--