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But my test cases are only for anonmous folios. >> while mapping_large_folio_support() is only reasonable for page >> cache folios. > > Agreed. > > I wonder if mapping_large_folio_support() should either > > a) Complain if used for anon folios, so we can detect the wrong use mor= e easily. (VM_WARN_ON_ONCE()) This is much better. > > b) Return "true" for anonymous mappings, although that's more debatable= =2E This might fix the warning here, but the function might get wrong uses ea= sily. > >> >> In split_huge_page_to_list_to_order(), the folio passed to >> mapping_large_folio_support() maybe anonmous folio. The >> folio_test_anon() check is missing. So the split of the anonmous THP >> is failed. This is also the same for shmem_mapping(). We'd better add >> a check for both. But the shmem_mapping() in __split_huge_page() is >> not involved, as for anonmous folios, the end parameter is set to -1, = so >> (head[i].index >=3D end) is always false. shmem_mapping() is not calle= d. >> >> Using /sys/kernel/debug/split_huge_pages to verify this, with this >> patch, large anon THP is successfully split and the warning is ceased.= >> >> Signed-off-by: Ran Xiaokai >> Cc: xu xin >> Cc: Yang Yang >> --- >> mm/huge_memory.c | 38 ++++++++++++++++++++------------------ >> 1 file changed, 20 insertions(+), 18 deletions(-) >> >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index 317de2afd371..4c9c7e5ea20c 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -3009,31 +3009,33 @@ int split_huge_page_to_list_to_order(struct pa= ge *page, struct list_head *list, >> if (new_order >=3D folio_order(folio)) >> return -EINVAL; >> >> - /* Cannot split anonymous THP to order-1 */ >> - if (new_order =3D=3D 1 && folio_test_anon(folio)) { >> - VM_WARN_ONCE(1, "Cannot split to order-1 folio"); >> - return -EINVAL; >> - } >> - >> if (new_order) { >> /* Only swapping a whole PMD-mapped folio is supported */ >> if (folio_test_swapcache(folio)) >> return -EINVAL; >> - /* Split shmem folio to non-zero order not supported */ >> - if (shmem_mapping(folio->mapping)) { >> - VM_WARN_ONCE(1, >> - "Cannot split shmem folio to non-0 order"); >> - return -EINVAL; >> - } >> - /* No split if the file system does not support large folio */ >> - if (!mapping_large_folio_support(folio->mapping)) { >> - VM_WARN_ONCE(1, >> - "Cannot split file folio to non-0 order"); >> - return -EINVAL; >> + >> + if (folio_test_anon(folio)) { >> + /* Cannot split anonymous THP to order-1 */ >> + if (new_order =3D=3D 1) { >> + VM_WARN_ONCE(1, "Cannot split to order-1 folio"); >> + return -EINVAL; >> + } >> + } else { >> + /* Split shmem folio to non-zero order not supported */ >> + if (shmem_mapping(folio->mapping)) { >> + VM_WARN_ONCE(1, >> + "Cannot split shmem folio to non-0 order"); >> + return -EINVAL; >> + } >> + /* No split if the file system does not support large folio */ >> + if (!mapping_large_folio_support(folio->mapping)) { >> + VM_WARN_ONCE(1, >> + "Cannot split file folio to non-0 order"); >> + return -EINVAL; >> + } >> } >> } > > What about the following sequence: > > if (folio_test_anon(folio)) { > if (new_order =3D=3D 1) > ... > } else if (new_order) { > if (shmem_mapping(...)) > ... > ... > } > > if (folio_test_swapcache(folio) && new_order) > return -EINVAL; > > Should result in less churn and reduce indentation level. Yeah, this looks better to me. Best Regards, Yan, Zi --=_MailMate_1DA8CF4E-A6E2-4232-9624-4A4273D7299D_= Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQJDBAEBCgAtFiEEh7yFAW3gwjwQ4C9anbJR82th+ooFAmZfHDYPHHppeUBudmlk aWEuY29tAAoJEJ2yUfNrYfqK4p8P/3Z00wHEG3jJ5l4vHPNvPA1fb9aeUraW5Tvn Y0xAcbNViss4cuFknKE6z0Aw65b3nb4lQZ9Ux7m8lbpeW8JKFraj2qAjg1yMl8ZT +e44orvEwbbUA9ga0ZlcATkWETb/hMYb1E1Wa090lToXU1CjtrWSLZeU0FTAeRQT SIoNqX4faWAs2p4hOAle+YUTzzdqbXTrowQwVhXxV8efB0x+RAv8qdJd4frWtio1 oBuSNTs/iUqFykXDsQekxDon1l4SW9bWvMKP2w9PsrIoP7iH49i1rqeOYNgCuQwW TbWiiQYzjm/8tN9VP4NVNR6ZKGIXS5RR48pIoIeqX9J8QsHM6S913NM+87wZL+0k AXFXKzRAIxvyJxMCw+GpfpZ22TQrlaTrtVRpX0J0cHiDSq/24Ff2vpDxB4r1aigp WbBhFSWgD1FBjouj5i2Op/yGhxL3XhZD4FV4TFx6XCzPJGUTY6aZ3iqFQ1pMIxLO uSdWQq37GmvcD4yxjoou1QaiutbfMo10otc8g9uVEpzAjOFwoKiON9lvxT9OrYJB wI1pitQv3CPXXkQcvdFRnFD/Xc569TOHkdAOn30peh9oYbzyhxmsHDR09eYf1s64 HHdG6QkrlR+01iCyzdVUOuAEa985ca7cM/CXO8Dk4tVT8OsLqA/AObTRZrwyMpDg KxhiF9mf =VAWf -----END PGP SIGNATURE----- --=_MailMate_1DA8CF4E-A6E2-4232-9624-4A4273D7299D_=--