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 8ONJPDZE aLsZapkxC7A8z8Fwl+MHuIDbNcby/Muke02n90RwNIVs1/VtO0CuR+8peIqTBGkhL1P4EXfO1SS41nbQk37aGE2BwJSehAQ5p907kr8wwBXpwZp44KrxwpP3HBV8snQpR41/HZj+U+TtOA1mZWlFoBcft6Eo69aGjZx3MfdD58aip34AQ5otr7MErIKafAg7dFGUQ/phT4v0ojLjCE6axTBNslwg1kzfeRXutnErLpOGP8VllbBIIABl9pW2UjWxQDg/1kOiNgu5rx3X5Z0BN0TtnfV23wrRR8uiFWhnaSKvbipoe6yLRl6qztk6oqjzfKS2Xf4YkE1HWZx0Y8Jc7fLSEpJd3orXiMTL1XnX0zua++YogvdkQHL3vtBFJwg53OLbgVMBJKFkfIZLBJLw6gKoC0OLyTSNtcALt/jke6L5jlv9uDdV0wzImtonwxw5QdinBvvzdRch8n85SxXrBWOzmvjhhwvx4HEOCmgp1YwiWgagZStas8IBEYZ6rcDrfaD2MsR1tjkzMB7x7EJa9aKHd9g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/14/25 14:21, Wei Yang wrote: > On Fri, Nov 14, 2025 at 12:22:28PM +1100, Balbir Singh wrote: > [...] >> @@ -4079,6 +4091,36 @@ static int __folio_split(struct folio *folio, unsigned int new_order, >> return ret; >> } >> >> +/* >> + * 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