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>> } >> >> +/* >> + * This function is a helper for splitting folios that have already been unmapped. >> + * The use case is that the device or the CPU can refuse to migrate THP pages in >> + * the middle of migration, due to allocation issues on either side >> + * >> + * The high level code is copied from __folio_split, since the pages are anonymous >> + * and are already isolated from the LRU, the code has been simplified to not >> + * burden __folio_split with unmapped sprinkled into the code. >> + * >> + * None of the split folios are unlocked >> + */ >> +int folio_split_unmapped(struct folio *folio, unsigned int new_order) >> +{ >> + int extra_pins, ret = 0; >> + >> + VM_WARN_ON_FOLIO(folio_mapped(folio), folio); >> + VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); >> + VM_WARN_ON_ONCE_FOLIO(!folio_test_large(folio), folio); >> + > > Compared with original logic, we did check folio_split_supported() and > check whether new_order is supported for the file system. > > Currently folio_split_unmapped() only pass 0 as new_order, which looks good. > But for a generic helper, it looks reasonable to do the check, IMHO. > This is meant to be used in the middle of a migration where the src/dst do no agree on the folio_order() due to allocation issues. When mTHP support is added to device migration, order support will be added and checked. FYI: This routines supports just anonymous pages ATM >> + if (!can_split_folio(folio, 1, &extra_pins)) >> + return -EAGAIN; >> + >> + local_irq_disable(); >> + ret = __folio_freeze_and_split_unmapped(folio, new_order, &folio->page, NULL, >> + NULL, false, NULL, SPLIT_TYPE_UNIFORM, >> + 0, extra_pins); >> + local_irq_enable(); >> + return ret; >> +} >> + >> /* >> * This function splits a large folio into smaller folios of order @new_order. >> * @page can point to any page of the large folio to split. The split operation > > Balbir