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On 4 Jun 2024, at 6:52, Zi Yan wrote: > On 4 Jun 2024, at 0:57, David Hildenbrand wrote: > >> On 04.06.24 07:47, xu.xin16@zte.com.cn wrote: >>> From: Ran Xiaokai >>> >>> When I did a large folios split test, a WARNING >>> "[ 5059.122759][ T166] Cannot split file folio to non-0 order" >>> was triggered. 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 mo= re easily. (VM_WARN_ON_ONCE()) > > This is much better. > >> >> b) Return "true" for anonymous mappings, although that's more debatabl= e. > > This might fix the warning here, but the function might get wrong uses = easily. > >> >>> >>> 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 call= ed. >>> >>> Using /sys/kernel/debug/split_huge_pages to verify this, with this >>> patch, large anon THP is successfully split and the warning is ceased= =2E >>> >>> 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 p= age *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 Best Regards, Yan, Zi --=_MailMate_01E4B2E9-59F6-41DB-96D2-C9FD75587B8B_= Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc -----BEGIN PGP SIGNATURE----- iQJDBAEBCgAtFiEEh7yFAW3gwjwQ4C9anbJR82th+ooFAmZfHUgPHHppeUBudmlk aWEuY29tAAoJEJ2yUfNrYfqKZREP/2JcrAqmQ85b4R30JsfmWOihbYj0UMpv25ih ZVDC+K4ceHYApboC2ijOIIQUE7lsmDWP1y5TlF1SivcRysn9wX3oSpaOUdqOTHRa tWiRI5A/e1LqzQsXFaW6N+O+sayR+3i58pjyGbp05e/bqYnEXnwR6Hju+B4VuEse YpwHPfyt0QR+CJ/pMRNOl06ZrmGP2eOUEFpZVRiZa7FO8xD0xbuNcB4Ze93m4X/R WNtD8g8ThVGRMeaD+yU22at/i1b9yfcO0tKbRN7Jxenh1E4tarXqccPFWqwckB9l sn2AgOn70tHnwr2AnxirLFFq7frKtkd3ef6gYyO+7OKmgYbVs04INQ3+TVQfOyRr 74QjVW/kmejoivWlzksYWKXfGOoCInmOqPnSXuahWnv5NH7muBUSqeOu31GU+Q6a vTLkrMkg1F/lN9uEHK7hzI6W58J5BM55JmXIhWO00ETqOeKV6sQncizt9WN8tzm9 d94dp8SYptvRfdT24OoYlW8R5iqQA5yAJJzIIDSpEha3qi5+f7DMLiiEP/HLS7x3 907mAItKzqzHjLk9S5CPHxqdu70nfCzuDfJLu4LC2/tgrIidN/Zhi4oyBhBayXjO eemcoI6YS2QqGllS/VPxuJTn0aZbuZls8U23Ul1N4SBgqAPRtITtSsSxlh4M1XWg MHMGm+/T =JihK -----END PGP SIGNATURE----- --=_MailMate_01E4B2E9-59F6-41DB-96D2-C9FD75587B8B_=--